Heat and Fluid
- Working Group
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Fluid Mechanics Laboratory
Responsible Faculty Member
- Makina Mühendisliği Binası (Z64)
- +90 232 750 6770
Heat & Mass Research Laboratory
Responsible Faculty Member
- Mechanical Engineering Building (142)
- +90 232 750 6744
Micro/Nano Engineering Laboratory
Responsible Faculty Member
- Mechanical Engineering Building (162)
- +90 232 750 6785
2023 |
Gocmen, Sinan; Cetkin, Erdal Experimental Investigation of Air Cooling With/Out Tab Cooling in Cell and Module Levels for Thermal Uniformity in Battery Packs Journal Article Journal of Heat Transfer, 145 (2), 2023. @article{Gocmen2023, title = {Experimental Investigation of Air Cooling With/Out Tab Cooling in Cell and Module Levels for Thermal Uniformity in Battery Packs}, author = {Sinan Gocmen and Erdal Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85143991374&doi=10.1115%2f1.4055939&partnerID=40&md5=efb2c14fb28632d261da28c8f71ad9c5}, doi = {10.1115/1.4055939}, year = {2023}, date = {2023-01-01}, journal = {Journal of Heat Transfer}, volume = {145}, number = {2}, abstract = {Catastrophic effects of global warming and environmental pollution are becoming more evident each day, and reduction in fossil fuel consumption is an urgent need. Thus, electric vehicles powered by sustainable energy sources are becoming a major interest. However, there are some challenges such as safety, limited range, long charging times, and battery life which are inhibitory to the adaptation of them. One of the biggest reasons for these challenges is the relationship between battery degradation and temperature which can be eliminated if batteries can be kept at the optimum temperature range. Here, the effects of three distinct (natural convection, forced convection, and tab cooling) methodology were experimentally compared at both the cell and module levels (six serial 7.5 Ah Kokam pouch cells, 1P6S) for thermal management of lithium-ion cells. The experiments were conducted at a discharge rate of 3C with ambient temperatures of 24 ◦C and 29 ◦C. The cell-level test results show that the tab cooling yields 32.5% better thermal uniformity in comparison to the other techniques. Furthermore, tab cooling yields better temperature uniformity with and without air convection as the hot spots occurring near the tabs is eliminated. For the module level, the forced air convection method stands out as the best option with a 4.3% temperature deviation between cells and maximum cell temperature of 39 ◦C. Overall, the results show that a hybrid approach with tab cooling would be beneficial in terms of temperature homogeneity especially in high capacity electric vehicle battery cells. Copyright © 2023 by ASME.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Catastrophic effects of global warming and environmental pollution are becoming more evident each day, and reduction in fossil fuel consumption is an urgent need. Thus, electric vehicles powered by sustainable energy sources are becoming a major interest. However, there are some challenges such as safety, limited range, long charging times, and battery life which are inhibitory to the adaptation of them. One of the biggest reasons for these challenges is the relationship between battery degradation and temperature which can be eliminated if batteries can be kept at the optimum temperature range. Here, the effects of three distinct (natural convection, forced convection, and tab cooling) methodology were experimentally compared at both the cell and module levels (six serial 7.5 Ah Kokam pouch cells, 1P6S) for thermal management of lithium-ion cells. The experiments were conducted at a discharge rate of 3C with ambient temperatures of 24 ◦C and 29 ◦C. The cell-level test results show that the tab cooling yields 32.5% better thermal uniformity in comparison to the other techniques. Furthermore, tab cooling yields better temperature uniformity with and without air convection as the hot spots occurring near the tabs is eliminated. For the module level, the forced air convection method stands out as the best option with a 4.3% temperature deviation between cells and maximum cell temperature of 39 ◦C. Overall, the results show that a hybrid approach with tab cooling would be beneficial in terms of temperature homogeneity especially in high capacity electric vehicle battery cells. Copyright © 2023 by ASME. |
Benim, Ali Cemal; Korucu, Ayse Computational investigation of non-premixed hydrogen-air laminar flames Journal Article International Journal of Hydrogen Energy, 2023. @article{Benim2023, title = {Computational investigation of non-premixed hydrogen-air laminar flames}, author = {Ali Cemal Benim and Ayse Korucu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85146346018&doi=10.1016%2fj.ijhydene.2022.12.248&partnerID=40&md5=89d0b1a520d385f2e21b07190741c33b}, doi = {10.1016/j.ijhydene.2022.12.248}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Hydrogen Energy}, abstract = {Laminar diffusion hydrogen/air flames are numerically investigated. Detailed and global mechanisms are compared. NO formation is modelled by full nitrogen chemistry and the extended Zeldovich mechanism. A satisfactory agreement between the present predictions and the experiments of other authors is observed. Significance of different ingredients of mathematical modelling is analyzed. Minor roles of thermal diffusion and radiation, but a significant role of buoyancy is observed. It is observed that the full and quasi multi-component diffusion deliver the same results, whereas assuming Le = 1 to a remarkable difference. NO emissions logarithmically increase with increasing residence time. NO is the dominating nitrogen oxide. Its share increases with residence time, whereby NO2 and N2O show a reverse trend. It is observed that the NNH route plays a remarkable role in NO formation, where the share of the Zeldovich mechanism increases with residence time from about 20% to 85%, within the considered range. © 2022 Hydrogen Energy Publications LLC}, keywords = {}, pubstate = {published}, tppubtype = {article} } Laminar diffusion hydrogen/air flames are numerically investigated. Detailed and global mechanisms are compared. NO formation is modelled by full nitrogen chemistry and the extended Zeldovich mechanism. A satisfactory agreement between the present predictions and the experiments of other authors is observed. Significance of different ingredients of mathematical modelling is analyzed. Minor roles of thermal diffusion and radiation, but a significant role of buoyancy is observed. It is observed that the full and quasi multi-component diffusion deliver the same results, whereas assuming Le = 1 to a remarkable difference. NO emissions logarithmically increase with increasing residence time. NO is the dominating nitrogen oxide. Its share increases with residence time, whereby NO2 and N2O show a reverse trend. It is observed that the NNH route plays a remarkable role in NO formation, where the share of the Zeldovich mechanism increases with residence time from about 20% to 85%, within the considered range. © 2022 Hydrogen Energy Publications LLC |
Toprak, Kasim; Bayazitoglu, Yildiz LONGITUDINAL THERMAL CONDUCTIVITY OF Cu-SWCNT CORE-SHELL NANOWIRE: MOLECULAR DYNAMICS SIMULATIONS Journal Article Heat Transfer Research, 54 (4), pp. 77 – 89, 2023. @article{Toprak202377, title = {LONGITUDINAL THERMAL CONDUCTIVITY OF Cu-SWCNT CORE-SHELL NANOWIRE: MOLECULAR DYNAMICS SIMULATIONS}, author = {Kasim Toprak and Yildiz Bayazitoglu}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85159154476&doi=10.1615%2fHeatTransRes.2022044425&partnerID=40&md5=f5dc57c56947ec56a143fb7cf8346175}, doi = {10.1615/HeatTransRes.2022044425}, year = {2023}, date = {2023-01-01}, journal = {Heat Transfer Research}, volume = {54}, number = {4}, pages = {77 – 89}, abstract = {The phonon thermal conductivity of copper core and armchair single-walled carbon nanotube shell (Cu-SWCNT) coaxial nanostructure is presented using the non-equilibrium molecular dynamics (NEMD) simulations method. The study aims to investigate how the ultrathin Cu nanowire affects the thermal conductivity of Cu-SWCNT. The results have revealed that the thermal conductivity of Cu-SWCNT is more than two orders of magnitude higher than that of the Cu core with the contribution of the SWCNT shell. The influences of length, chirality, defect, and core filling on the thermal conductivity of Cu-SWCNT are studied using the two most used C-C potentials, the AIREBO and Tersoff potentials. The bare SWCNT and Cu-SWCNT simulation results revealed that the thermal conductivity using the AIREBO potential is lower than that of Tersoff. Although the thermal conductivity increases with the length of the coaxial tube, it decreases with the chirality and the filling ratio. Increasing the chirality of SWCNT and the Cu core-filling ratio can boost the core copper's contributions to the thermal conductivity, reducing the overall thermal conductivity. The lengths of the thermostat and buffer regions do not significantly affect the thermal conductivity. In addition, the vacancy concentration in heat flow regions effectively reduces thermal conductivity, whereas the vacancy in the thermostat regions does not have a significant effect. The thermal rectification factor defined as changing the imposed heat flux direction is up to 1.73%for the Cu-SWCNT and 2.63% for the SWCNT. © 2023 by Begell House, Inc.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The phonon thermal conductivity of copper core and armchair single-walled carbon nanotube shell (Cu-SWCNT) coaxial nanostructure is presented using the non-equilibrium molecular dynamics (NEMD) simulations method. The study aims to investigate how the ultrathin Cu nanowire affects the thermal conductivity of Cu-SWCNT. The results have revealed that the thermal conductivity of Cu-SWCNT is more than two orders of magnitude higher than that of the Cu core with the contribution of the SWCNT shell. The influences of length, chirality, defect, and core filling on the thermal conductivity of Cu-SWCNT are studied using the two most used C-C potentials, the AIREBO and Tersoff potentials. The bare SWCNT and Cu-SWCNT simulation results revealed that the thermal conductivity using the AIREBO potential is lower than that of Tersoff. Although the thermal conductivity increases with the length of the coaxial tube, it decreases with the chirality and the filling ratio. Increasing the chirality of SWCNT and the Cu core-filling ratio can boost the core copper's contributions to the thermal conductivity, reducing the overall thermal conductivity. The lengths of the thermostat and buffer regions do not significantly affect the thermal conductivity. In addition, the vacancy concentration in heat flow regions effectively reduces thermal conductivity, whereas the vacancy in the thermostat regions does not have a significant effect. The thermal rectification factor defined as changing the imposed heat flux direction is up to 1.73%for the Cu-SWCNT and 2.63% for the SWCNT. © 2023 by Begell House, Inc. |
İplikçi, Hande; Barisik, Murat; Türkdoğan, Ceren; Martin, Seçkin; Yeke, Melisa; Nuhoğlu, Kaan; Esenoğlu, Gözde; Tanoğlu, Metin; Aktaş, Engin; Dehneliler, Serkan; İriş, Mehmet Erdem Effects of nanosecond laser ablation parameters on surface modification of carbon fiber reinforced polymer composites Journal Article Journal of Composite Materials, 57 (18), pp. 2843 – 2855, 2023. @article{İplikçi20232843, title = {Effects of nanosecond laser ablation parameters on surface modification of carbon fiber reinforced polymer composites}, author = {Hande İplikçi and Murat Barisik and Ceren Türkdoğan and Seçkin Martin and Melisa Yeke and Kaan Nuhoğlu and Gözde Esenoğlu and Metin Tanoğlu and Engin Aktaş and Serkan Dehneliler and Mehmet Erdem İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85162945413&doi=10.1177%2f00219983231178892&partnerID=40&md5=1e698a002a7d62e7f42a2444aafff1d5}, doi = {10.1177/00219983231178892}, year = {2023}, date = {2023-01-01}, journal = {Journal of Composite Materials}, volume = {57}, number = {18}, pages = {2843 – 2855}, abstract = {Removal of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/−45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Removal of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/−45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition. © The Author(s) 2023. |
Esenoğlu, Gözde; Tanoğlu, Metin; Barisik, Murat; İplikçi, Hande; Yeke, Melisa; Nuhoğlu, Kaan; Türkdoğan, Ceren; Martin, Seçkin; Aktaş, Engin; Dehneliler, Serkan; Gürbüz, Ahmet Ayberk; İriş, Mehmet Erdem Investigating the Effects of PA66 Electrospun Nanofibers Layered within an Adhesive Composite Joint Fabricated under Autoclave Curing Journal Article ACS Omega, 8 (36), pp. 32656 – 32666, 2023, (All Open Access, Gold Open Access, Green Open Access). @article{Esenoğlu202332656, title = {Investigating the Effects of PA66 Electrospun Nanofibers Layered within an Adhesive Composite Joint Fabricated under Autoclave Curing}, author = {Gözde Esenoğlu and Metin Tanoğlu and Murat Barisik and Hande İplikçi and Melisa Yeke and Kaan Nuhoğlu and Ceren Türkdoğan and Seçkin Martin and Engin Aktaş and Serkan Dehneliler and Ahmet Ayberk Gürbüz and Mehmet Erdem İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85172448706&doi=10.1021%2facsomega.3c03419&partnerID=40&md5=7f3ddea2390eb013c802b710a5aaf695}, doi = {10.1021/acsomega.3c03419}, year = {2023}, date = {2023-01-01}, journal = {ACS Omega}, volume = {8}, number = {36}, pages = {32656 – 32666}, abstract = {Enhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant. © 2023 The Authors. Published by American Chemical Society.}, note = {All Open Access, Gold Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Enhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant. © 2023 The Authors. Published by American Chemical Society. |
Gungor, Sahin; Gocmen, Sinan; Cetkin, Erdal A review on battery thermal management strategies in lithium-ion and post-lithium batteries for electric vehicles Journal Article Journal of Thermal Engineering, 9 (4), pp. 1078 – 1099, 2023, (All Open Access, Gold Open Access, Green Open Access). @article{Gungor20231078, title = {A review on battery thermal management strategies in lithium-ion and post-lithium batteries for electric vehicles}, author = {Sahin Gungor and Sinan Gocmen and Erdal Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85169015170&doi=10.18186%2fthermal.1334238&partnerID=40&md5=263294fb861dd4fbc4a7751e2bb7079d}, doi = {10.18186/thermal.1334238}, year = {2023}, date = {2023-01-01}, journal = {Journal of Thermal Engineering}, volume = {9}, number = {4}, pages = {1078 – 1099}, abstract = {Electrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conventional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and structure of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as layer degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are documented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries. © Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).}, note = {All Open Access, Gold Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electrification on transportation and electricity generation via renewable sources play a vital role to diminish the effects of energy usage on the environment. Transition from the conventional fuels to renewables for transportation and electricity generation demands the storage of electricity in great capacities with desired power densities and relatively high C-rate values. Yet, thermal and electrical characteristics vary greatly depending on the chemistry and structure of battery cells. At this point, lithium-ion (Li-ion) batteries are more suitable in most applications due to their superiorities such as long lifetime, high recyclability, and capacities. However, exothermic electrochemical reactions yield temperature to increase suddenly which affects the degradation in cells, ageing, and electrochemical reaction kinetics. Therefore, strict temperature control increases battery lifetime and eliminates undesired situations such as layer degradation and thermal runaway. In the literature, there are many distinct battery thermal management strategies to effectively control battery cell temperatures. These strategies vary based on the geometrical form, size, capacity, and chemistry of the battery cells. Here, we focus on proposed battery thermal management strategies and current applications in the electric vehicle (EV) industry. In this review, various battery thermal management strategies are documented and compared in detail with respect to geometry, thermal uniformity, coolant type and heat transfer methodology for Li-ion and post-lithium batteries. © Copyright 2021, Yıldız Technical University. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). |
Coşkun, Turgay; Çetkin, Erdal Vascularized mini cooling channels to achieve temperature uniformity: Battery thermal management and electronic cooling Journal Article Research on Engineering Structures and Materials, 9 (3), pp. 375 – 385, 2023, (All Open Access, Bronze Open Access). @article{Coşkun2023375, title = {Vascularized mini cooling channels to achieve temperature uniformity: Battery thermal management and electronic cooling}, author = {Turgay Coşkun and Erdal Çetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85172141689&doi=10.17515%2fresm2022.585ma1121&partnerID=40&md5=9ad60c3fb4eeb671fd48e7749faec21d}, doi = {10.17515/resm2022.585ma1121}, year = {2023}, date = {2023-01-01}, journal = {Research on Engineering Structures and Materials}, volume = {9}, number = {3}, pages = {375 – 385}, abstract = {Here we propose to use of distinct vascularized plates to be used in the applications of battery thermal management and electronic cooling. The temperatures of battery cells increase during charge and discharge; and elevated temperature values in them accelerated degradation and even may trigger battery fire because of the thermal runaway. Therefore, thermal management system is a necessity for battery packs to increase the battery performance and diminish the risk factors in the electric vehicles. Generally, high amount of heat is released in the high capacity (>15 Ah) cells in short time interval under fast charge/discharge conditions; thus, thermal management of the battery system can be achieved with liquid cooling in that situation. A silicon heater system which represents the thermal behavior of a battery cell is manufactured based on the literature and it is used in experiments. Such a method has not proposed up to now in the literature, so the study may be creating a new experimental procedure for future studies without the risk of battery fire/degradation to uncover even extreme conditions experimentally. Electronic cooling is also in prime importance due to enhanced computing requirement of current systems, and vascularized plates can solve the hot spot problems occurring with decreased energy consumption. According to the results, the cooling capacity of the vascularized plates are calculated as 20W, and a battery cell can be kept within its optimal operating temperature range when the heat loads up to 30W. Also, the temperature uniformity along the surface of mimic of the battery is satisfied by vascularized plates. © 2023 MIM Research Group. All rights reserved.}, note = {All Open Access, Bronze Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we propose to use of distinct vascularized plates to be used in the applications of battery thermal management and electronic cooling. The temperatures of battery cells increase during charge and discharge; and elevated temperature values in them accelerated degradation and even may trigger battery fire because of the thermal runaway. Therefore, thermal management system is a necessity for battery packs to increase the battery performance and diminish the risk factors in the electric vehicles. Generally, high amount of heat is released in the high capacity (>15 Ah) cells in short time interval under fast charge/discharge conditions; thus, thermal management of the battery system can be achieved with liquid cooling in that situation. A silicon heater system which represents the thermal behavior of a battery cell is manufactured based on the literature and it is used in experiments. Such a method has not proposed up to now in the literature, so the study may be creating a new experimental procedure for future studies without the risk of battery fire/degradation to uncover even extreme conditions experimentally. Electronic cooling is also in prime importance due to enhanced computing requirement of current systems, and vascularized plates can solve the hot spot problems occurring with decreased energy consumption. According to the results, the cooling capacity of the vascularized plates are calculated as 20W, and a battery cell can be kept within its optimal operating temperature range when the heat loads up to 30W. Also, the temperature uniformity along the surface of mimic of the battery is satisfied by vascularized plates. © 2023 MIM Research Group. All rights reserved. |
Naseri, F; Gil, S; Barbu, C; Cetkin, E; Yarimca, G; Jensen, A C; Larsen, P G; Gomes, C Digital twin of electric vehicle battery systems: Comprehensive review of the use cases, requirements, and platforms Journal Article Renewable and Sustainable Energy Reviews, 179 , 2023, (All Open Access, Green Open Access, Hybrid Gold Open Access). @article{Naseri2023, title = {Digital twin of electric vehicle battery systems: Comprehensive review of the use cases, requirements, and platforms}, author = {F Naseri and S Gil and C Barbu and E Cetkin and G Yarimca and A C Jensen and P G Larsen and C Gomes}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85152416376&doi=10.1016%2fj.rser.2023.113280&partnerID=40&md5=cecb165a2389d2006c18cb72ba49eb6e}, doi = {10.1016/j.rser.2023.113280}, year = {2023}, date = {2023-01-01}, journal = {Renewable and Sustainable Energy Reviews}, volume = {179}, abstract = {Transportation electrification has been fueled by recent advancements in the technology and manufacturing of battery systems, but the industry yet is facing serious challenges that could be addressed using cutting-edge digital technologies. One such novel technology is based on the digital twining of battery systems. Digital twins (DTs) of batteries utilize advanced multi-layer models, artificial intelligence, advanced sensing units, Internet-of-Things technologies, and cloud computing techniques to provide a virtual live representation of the real battery system (the physical twin) to improve the performance, safety, and cost-effectiveness. Furthermore, they orchestrate the operation of the entire battery value chain offering great advantages, such as improving the economy of manufacturing, re-purposing, and recycling processes. In this context, various studies have been carried out discussing the DT applications and use cases from cloud-enabled battery management systems to the digitalization of battery testing. This work provides a comprehensive review of different possible use cases, key enabling technologies, and requirements for battery DTs. The review inclusively discusses the use cases, development/integration platforms, as well as hardware and software requirements for implementation of the battery DTs, including electrical topics related to the modeling and algorithmic approaches, software architectures, and digital platforms for DT development and integration. The existing challenges are identified and circumstances that will create enough value to justify these challenges, such as the added costs, are discussed. © 2023 The Authors}, note = {All Open Access, Green Open Access, Hybrid Gold Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Transportation electrification has been fueled by recent advancements in the technology and manufacturing of battery systems, but the industry yet is facing serious challenges that could be addressed using cutting-edge digital technologies. One such novel technology is based on the digital twining of battery systems. Digital twins (DTs) of batteries utilize advanced multi-layer models, artificial intelligence, advanced sensing units, Internet-of-Things technologies, and cloud computing techniques to provide a virtual live representation of the real battery system (the physical twin) to improve the performance, safety, and cost-effectiveness. Furthermore, they orchestrate the operation of the entire battery value chain offering great advantages, such as improving the economy of manufacturing, re-purposing, and recycling processes. In this context, various studies have been carried out discussing the DT applications and use cases from cloud-enabled battery management systems to the digitalization of battery testing. This work provides a comprehensive review of different possible use cases, key enabling technologies, and requirements for battery DTs. The review inclusively discusses the use cases, development/integration platforms, as well as hardware and software requirements for implementation of the battery DTs, including electrical topics related to the modeling and algorithmic approaches, software architectures, and digital platforms for DT development and integration. The existing challenges are identified and circumstances that will create enough value to justify these challenges, such as the added costs, are discussed. © 2023 The Authors |
Coşkun, Turgay; Çetkin, Erdal Cold plate enabling air and liquid cooling simultaneously: Experimental study for battery pack thermal management and electronic cooling Journal Article International Journal of Heat and Mass Transfer, 217 , 2023. @article{Coşkun2023b, title = {Cold plate enabling air and liquid cooling simultaneously: Experimental study for battery pack thermal management and electronic cooling}, author = {Turgay Coşkun and Erdal Çetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85171470128&doi=10.1016%2fj.ijheatmasstransfer.2023.124702&partnerID=40&md5=1857b720cbfc7b433f17d682d0c99b3a}, doi = {10.1016/j.ijheatmasstransfer.2023.124702}, year = {2023}, date = {2023-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {217}, abstract = {The temperature of cells varies greatly during dis/charge while their performance and lifetime are greatly affected by this fluctuation. Elevated temperatures may yield battery fire due to thermal runaway as well they accelerate ageing and capacity fade of cells. Thermal management systems are a necessity for electric vehicles to extend the lifetime of battery cells and eliminate any fire risks, especially for fast dis/charging applications. Here, we document a hybrid cold plate with a working fluid(s) of sole air or liquid as well as both of them. Hybridization of air and liquid cooling promises to minimize energy consumption requirements during a charge/discharge cycle by combining the benefits of both thermal management strategies if energy management is controlled accordingly. The temperature of each cell can be kept below 30°C with the proposed hybrid cooling heat exchanger, and the temperature difference between the cells is reduced by 30 % relative to liquid cooling. The maximum temperatures are decreased by 18 % and 3 % in hybrid cooling when compared to air and water cooling, respectively. Furthermore, a step function combining various discharge rates (1C and 3C) was employed in experiments to mimic a realistic situation, i.e. variable C-rate rather than constant. The results show that the temperature of the battery cells can be kept below 30°C with air cooling for variable discharge rate and the effect of contact resistance should not be overlooked for liquid cooling. Furthermore, the possible use of the proposed hybrid cold plates is surveyed in the cooling of electronic devices which produce more and continuous heat than cells. Therefore, three resistance heaters with a capacity of 50W are used in experiments as well. The results show that the proposed cold plates could be used in both electronics cooling and battery thermal management with a control algorithm to switch between sole working fluid and combination modes which could be developed based on the results of this paper. © 2023}, keywords = {}, pubstate = {published}, tppubtype = {article} } The temperature of cells varies greatly during dis/charge while their performance and lifetime are greatly affected by this fluctuation. Elevated temperatures may yield battery fire due to thermal runaway as well they accelerate ageing and capacity fade of cells. Thermal management systems are a necessity for electric vehicles to extend the lifetime of battery cells and eliminate any fire risks, especially for fast dis/charging applications. Here, we document a hybrid cold plate with a working fluid(s) of sole air or liquid as well as both of them. Hybridization of air and liquid cooling promises to minimize energy consumption requirements during a charge/discharge cycle by combining the benefits of both thermal management strategies if energy management is controlled accordingly. The temperature of each cell can be kept below 30°C with the proposed hybrid cooling heat exchanger, and the temperature difference between the cells is reduced by 30 % relative to liquid cooling. The maximum temperatures are decreased by 18 % and 3 % in hybrid cooling when compared to air and water cooling, respectively. Furthermore, a step function combining various discharge rates (1C and 3C) was employed in experiments to mimic a realistic situation, i.e. variable C-rate rather than constant. The results show that the temperature of the battery cells can be kept below 30°C with air cooling for variable discharge rate and the effect of contact resistance should not be overlooked for liquid cooling. Furthermore, the possible use of the proposed hybrid cold plates is surveyed in the cooling of electronic devices which produce more and continuous heat than cells. Therefore, three resistance heaters with a capacity of 50W are used in experiments as well. The results show that the proposed cold plates could be used in both electronics cooling and battery thermal management with a control algorithm to switch between sole working fluid and combination modes which could be developed based on the results of this paper. © 2023 |
Korucu, Ayşe; Miller, Richard Journal of the Faculty of Engineering and Architecture of Gazi University, 39 (1), pp. 91 – 99, 2023, (All Open Access, Bronze Open Access). @article{Korucu202391, title = {Differential diffusion and pressure effects on heavily sooting 2D Kerosene/Air shear flames; [Yüksek derecede kurum üreten 2B Gazyağı/Hava difüzyon alevleri üzerinde diferansiyel difüzyonun ve basıncın etkileri]}, author = {Ayşe Korucu and Richard Miller}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85174150376&doi=10.17341%2fgazimmfd.1153044&partnerID=40&md5=83c25552abccd22fffbfce453c52ba54}, doi = {10.17341/gazimmfd.1153044}, year = {2023}, date = {2023-01-01}, journal = {Journal of the Faculty of Engineering and Architecture of Gazi University}, volume = {39}, number = {1}, pages = {91 – 99}, abstract = {(Figure Presented). Purpose: The current study aims to test the limits of the Unity Lewis number simplification coupled with both the ideal gas (IGL) and a real gas (RGL) equation of state (EOS) for predicting flame and soot characteristics of heavily sooting Kerosene/Air shear flames at 4 different operating pressures. Theory and Methods: Fully compressible Navier-Stokes equations are adopted in DNS environment. For the computational mesh, equivalently spaced grid points from 0 < x1 < L1 are used, while in the cross-stream direction the mesh has been stretched in the x2 direction. An 8th order central explicit finite difference method and a 4th order Runge-Kutta are employed to solve for the spatial and time derivatives, respectively. The temperature contour plot created using 2D DNS data are provided in Figure A. Boundary conditions of the problem: I - in x2 direction, far from the flame kernel, flow is set to have free stream characteristics and II - in x1 direction, periodic boundary conditions are embedded to solve the turbulent flow. Results: Comparisons to the earlier studies have been revealed that the mean peak flame temperature predictions done by the unity-Le number model are lessened; implying that the soot production/oxidation rates calculations will be debilitated comparably to the low mean flame temperature of the unity-Le number cases regardless of the operating pressure. The unity-Le number model’s under-prediction of the flame temperatures results in intensifying incomplete combustion which not only emanates the soot load but also weaken the soot oxidation rate for the RGL EOS cases, while causes under-prediction of mass fraction of soot for the IGL EOS cases in comparison to the non-unity Le number results. As the operating pressure increases to 35 atm, the mean flame temperature increases hence, the soot load in the flame kernels increases even though the soot oxidation process is enhanced by the increasing flame temperature. An increase in the mean flame temperature has been noted for the IGL EOS model predictions at 35 atm case, which will cause an inevitable increment in soot load throughout the flame kernel. Conclusion: The analyses have revealed the that the unity-Le number simplification estimates the average flame temperature lower than expected for each operating pressure increasing the possibility of an incomplete combustion or even local flame weakening and extinction which stems ‘abnormally’ high soot load throughout the flame kernel essentially for 10 and 35 atm operating pressure cases of the IGL EOS model. © 2023 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.}, note = {All Open Access, Bronze Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } (Figure Presented). Purpose: The current study aims to test the limits of the Unity Lewis number simplification coupled with both the ideal gas (IGL) and a real gas (RGL) equation of state (EOS) for predicting flame and soot characteristics of heavily sooting Kerosene/Air shear flames at 4 different operating pressures. Theory and Methods: Fully compressible Navier-Stokes equations are adopted in DNS environment. For the computational mesh, equivalently spaced grid points from 0 < x1 < L1 are used, while in the cross-stream direction the mesh has been stretched in the x2 direction. An 8th order central explicit finite difference method and a 4th order Runge-Kutta are employed to solve for the spatial and time derivatives, respectively. The temperature contour plot created using 2D DNS data are provided in Figure A. Boundary conditions of the problem: I - in x2 direction, far from the flame kernel, flow is set to have free stream characteristics and II - in x1 direction, periodic boundary conditions are embedded to solve the turbulent flow. Results: Comparisons to the earlier studies have been revealed that the mean peak flame temperature predictions done by the unity-Le number model are lessened; implying that the soot production/oxidation rates calculations will be debilitated comparably to the low mean flame temperature of the unity-Le number cases regardless of the operating pressure. The unity-Le number model’s under-prediction of the flame temperatures results in intensifying incomplete combustion which not only emanates the soot load but also weaken the soot oxidation rate for the RGL EOS cases, while causes under-prediction of mass fraction of soot for the IGL EOS cases in comparison to the non-unity Le number results. As the operating pressure increases to 35 atm, the mean flame temperature increases hence, the soot load in the flame kernels increases even though the soot oxidation process is enhanced by the increasing flame temperature. An increase in the mean flame temperature has been noted for the IGL EOS model predictions at 35 atm case, which will cause an inevitable increment in soot load throughout the flame kernel. Conclusion: The analyses have revealed the that the unity-Le number simplification estimates the average flame temperature lower than expected for each operating pressure increasing the possibility of an incomplete combustion or even local flame weakening and extinction which stems ‘abnormally’ high soot load throughout the flame kernel essentially for 10 and 35 atm operating pressure cases of the IGL EOS model. © 2023 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved. |
2022 |
Gungor, Sahin; Cetkin, Erdal; Lorente, Sylvie Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 182 , 2022. @article{WOS:000709733600003, title = {Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach}, author = {Sahin Gungor and Erdal Cetkin and Sylvie Lorente}, doi = {10.1016/j.ijheatmasstransfer.2021.121918}, year = {2022}, date = {2022-01-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {182}, abstract = {With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. (c) 2021 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. (c) 2021 Elsevier Ltd. All rights reserved. |
Yenigun, O; Barisik, M Active heat transfer enhancement by interface-localized liquid dielectrophoresis using interdigitated electrodes Journal Article Carbon, 189 , pp. 339-348, 2022. @article{Yenigun2022339, title = {Active heat transfer enhancement by interface-localized liquid dielectrophoresis using interdigitated electrodes}, author = {O Yenigun and M Barisik}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85122100118&doi=10.1016%2fj.carbon.2021.12.063&partnerID=40&md5=070297f8e7ae2a455bbb8996fe221608}, doi = {10.1016/j.carbon.2021.12.063}, year = {2022}, date = {2022-01-01}, journal = {Carbon}, volume = {189}, pages = {339-348}, abstract = {We introduced an active heat transfer control between graphene and water using interdigitated electrodes (IDEs). Oppositely charged co-planer electrodes embedded on a graphene surface created a non-uniform electric field. Resulted interface localized liquid dielectrophoresis (LDEP) perpendicular to surface enhanced the water/graphene coupling and decreased interfacial thermal resistance (ITR) substantially. We correlated the theoretical calculations of average electric field strength near surface with Kapitza values measured at corresponding electrode configurations. We obtained a unified linear variation of Kapitza as a function of average electric strength independent of electrode size and charge. By increasing the electric field strength, we measured up to 96% decrease of Kapitza near electrodes. Since the IDEs generated electric field was only interface localized, it required lower electrode charges than any parallel-plate capacitor systems. We showed that ITR remains effective in heat transfer behavior for systems as big as 100nm such that interface localized electric field can at least increase the heat removal 50% by eliminating the ITR from both graphene/water interfaces of a channel system. By converting hydrophobic few-layer graphene to super-hydrophilic condition with ultra-low Kapitza, current results are important for graphene-based materials considered for the solution of the thermal management problem of current and next generation micro/nano-electronics. © 2021}, keywords = {}, pubstate = {published}, tppubtype = {article} } We introduced an active heat transfer control between graphene and water using interdigitated electrodes (IDEs). Oppositely charged co-planer electrodes embedded on a graphene surface created a non-uniform electric field. Resulted interface localized liquid dielectrophoresis (LDEP) perpendicular to surface enhanced the water/graphene coupling and decreased interfacial thermal resistance (ITR) substantially. We correlated the theoretical calculations of average electric field strength near surface with Kapitza values measured at corresponding electrode configurations. We obtained a unified linear variation of Kapitza as a function of average electric strength independent of electrode size and charge. By increasing the electric field strength, we measured up to 96% decrease of Kapitza near electrodes. Since the IDEs generated electric field was only interface localized, it required lower electrode charges than any parallel-plate capacitor systems. We showed that ITR remains effective in heat transfer behavior for systems as big as 100nm such that interface localized electric field can at least increase the heat removal 50% by eliminating the ITR from both graphene/water interfaces of a channel system. By converting hydrophobic few-layer graphene to super-hydrophilic condition with ultra-low Kapitza, current results are important for graphene-based materials considered for the solution of the thermal management problem of current and next generation micro/nano-electronics. © 2021 |
Sabet, S; Barisik, M; Buonomo, B; Manca, O Thermal and hydrodynamic behavior of forced convection gaseous slip flow in a Kelvin cell metal foam Journal Article International Communications in Heat and Mass Transfer, 131 , 2022. @article{Sabet2022, title = {Thermal and hydrodynamic behavior of forced convection gaseous slip flow in a Kelvin cell metal foam}, author = {S Sabet and M Barisik and B Buonomo and O Manca}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85121421292&doi=10.1016%2fj.icheatmasstransfer.2021.105838&partnerID=40&md5=014f7a382ce37a13408f90bd5c6be444}, doi = {10.1016/j.icheatmasstransfer.2021.105838}, year = {2022}, date = {2022-01-01}, journal = {International Communications in Heat and Mass Transfer}, volume = {131}, abstract = {Porous metallic foams are a key material in numerous thermal and hydraulic applications. Gas flows in such micro/nanoporous systems deviate from classical continuum descriptions due to nonequilibrium in gas dynamics, and the resulted heat and mass transport show variation by rarefaction. This study performed a wide range of pore-level analysis of convective gas flows in a Kelvin cell model at different porosities and working conditions. Rarefaction effects onto permeability and heat transfer coefficients were calculated through Darcy to Forchheimer flow regimes. Permeability increased up to 60% by increasing rarefaction while this enhancement decreased by increasing porosity. At the same time, rarefaction lessened inertial effects such that Forchheimer coefficients decreased substantially. At high flow velocities, the increase in rarefaction considerably decreased the effect of drag forces. Hence, hydrodynamic enhancement due to rarefaction was found to increase by increasing Reynolds number. On the other hand, positive influence of boundary slip and negative influence of temperature jump developing between gas and solid almost canceled each other for the studied low heat flux region of highly conductive metal foam structures. Hence, Nusselt numbers were found mostly related to Reynolds number independent from rarefaction. We described Nusselt value based on power law model as a function of Reynolds and porosity. Results and the proposed model are important to accurately predict the thermal and hydrodynamic performance of metal foams in the 80 PPI range. © 2021}, keywords = {}, pubstate = {published}, tppubtype = {article} } Porous metallic foams are a key material in numerous thermal and hydraulic applications. Gas flows in such micro/nanoporous systems deviate from classical continuum descriptions due to nonequilibrium in gas dynamics, and the resulted heat and mass transport show variation by rarefaction. This study performed a wide range of pore-level analysis of convective gas flows in a Kelvin cell model at different porosities and working conditions. Rarefaction effects onto permeability and heat transfer coefficients were calculated through Darcy to Forchheimer flow regimes. Permeability increased up to 60% by increasing rarefaction while this enhancement decreased by increasing porosity. At the same time, rarefaction lessened inertial effects such that Forchheimer coefficients decreased substantially. At high flow velocities, the increase in rarefaction considerably decreased the effect of drag forces. Hence, hydrodynamic enhancement due to rarefaction was found to increase by increasing Reynolds number. On the other hand, positive influence of boundary slip and negative influence of temperature jump developing between gas and solid almost canceled each other for the studied low heat flux region of highly conductive metal foam structures. Hence, Nusselt numbers were found mostly related to Reynolds number independent from rarefaction. We described Nusselt value based on power law model as a function of Reynolds and porosity. Results and the proposed model are important to accurately predict the thermal and hydrodynamic performance of metal foams in the 80 PPI range. © 2021 |
Sahin, R C; Gocmen, S; Cetkin, E Thermal management system for air-cooled battery packs with flow-disturbing structures Journal Article Journal of Power Sources, 551 , 2022. @article{Sahin2022b, title = {Thermal management system for air-cooled battery packs with flow-disturbing structures}, author = {R C Sahin and S Gocmen and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85140273371&doi=10.1016%2fj.jpowsour.2022.232214&partnerID=40&md5=b488f0477918b1e6b4dd91f0627d4578}, doi = {10.1016/j.jpowsour.2022.232214}, year = {2022}, date = {2022-01-01}, journal = {Journal of Power Sources}, volume = {551}, abstract = {Lithium-ion battery packs are preferred in electrical vehicles (EVs) due to their efficient and stable characteristics. Battery thermal management systems (BTMS) have vital importance in EVs to keep batteries in the desired temperature range to maximize performance and lifetime. BTMS with air cooling is simpler and lighter relative to competing methods; however, low thermal conductivity and heat capacity of air necessitate thermal performance and pressure drop adjustments. This work offers a novel design method for cylindrical cells by evaluating the effect of various baffles (cylindrical, triangular, diamond and winglet) on the cooling performance and pressure drop of an air-cooled battery module with 12 21700 cylindrical cells. Thermal characteristics are simulated by the electrochemical-thermal battery model, the P3D multiscale model (modelling parameters for a commercial 21700 cell are documented) in COMSOL Multiphysics 5.5 and their accuracy is validated by experiments. As a result, baffles reduce the maximum temperature and temperature difference by 5% (1.8 °C) and 40% (1.7 °C), respectively, consuming 3.5 times more power than the base design. Delta winglets offer the optimum solution, reducing the maximum temperature and temperature difference by 2% (0.6 °C) and 15% (0.7 °C), respectively, with a 44% (0.12 W) rise in parasitic power consumption. © 2022 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Lithium-ion battery packs are preferred in electrical vehicles (EVs) due to their efficient and stable characteristics. Battery thermal management systems (BTMS) have vital importance in EVs to keep batteries in the desired temperature range to maximize performance and lifetime. BTMS with air cooling is simpler and lighter relative to competing methods; however, low thermal conductivity and heat capacity of air necessitate thermal performance and pressure drop adjustments. This work offers a novel design method for cylindrical cells by evaluating the effect of various baffles (cylindrical, triangular, diamond and winglet) on the cooling performance and pressure drop of an air-cooled battery module with 12 21700 cylindrical cells. Thermal characteristics are simulated by the electrochemical-thermal battery model, the P3D multiscale model (modelling parameters for a commercial 21700 cell are documented) in COMSOL Multiphysics 5.5 and their accuracy is validated by experiments. As a result, baffles reduce the maximum temperature and temperature difference by 5% (1.8 °C) and 40% (1.7 °C), respectively, consuming 3.5 times more power than the base design. Delta winglets offer the optimum solution, reducing the maximum temperature and temperature difference by 2% (0.6 °C) and 15% (0.7 °C), respectively, with a 44% (0.12 W) rise in parasitic power consumption. © 2022 Elsevier B.V. |
Gungor, S; Cetkin, E Enhanced temperature uniformity with minimized pressure drop in electric vehicle battery packs at elevated C-rates Journal Article Heat Transfer, 51 (8), pp. 7540-7561, 2022. @article{Gungor20227540, title = {Enhanced temperature uniformity with minimized pressure drop in electric vehicle battery packs at elevated C-rates}, author = {S Gungor and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85135263580&doi=10.1002%2fhtj.22654&partnerID=40&md5=3b91b531fb44340686649125afd2a02a}, doi = {10.1002/htj.22654}, year = {2022}, date = {2022-01-01}, journal = {Heat Transfer}, volume = {51}, number = {8}, pages = {7540-7561}, abstract = {The trend of transition from fossil fuel to electrification in transportation is a result of no carbon emission produced by electric vehicles (EVs) during their daily operations. Furthermore, the global carbon footprint of EVs can be minimized if the electricity is generated from renewable sources such as wind and solar. On the other hand, there are some drawbacks of these vehicles such as charging time being very long and the mileage range of vehicles not at the desired level. Battery cells are being charged at relatively high C-rates to eliminate these problems, yet high current rates accelerate the aging of batteries and capacity losses due to the generated heat. Generated heat causes overheating, and excess temperature triggers degradation and thermal runaway risks. This paper uncovers how the battery pack temperature uniformity and strict thermal control can be achieved with heat transfer enhancement by conduction (cold plates) and convection (vascular channels). We aimed to reduce the energy consumption of the EV battery pack system while increasing the thermal performance. The impact of the thermal contact resistance is also considered for many realistic scenarios. The results indicate that an integrated system with cold plates and vascular channels satisfies the temperature uniformity requirement (over 81%) with comparatively less pumping power (∼72%) of advanced electric vehicles for relatively high C-rates. Furthermore, findings show the temperature level can increase up to 4°C as thermal contact resistance increases. The proposed cooling technique, which has low cost, easy application, and lower energy consumption superiorities, can be implemented in palpable EV battery packs. © 2022 Wiley Periodicals LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The trend of transition from fossil fuel to electrification in transportation is a result of no carbon emission produced by electric vehicles (EVs) during their daily operations. Furthermore, the global carbon footprint of EVs can be minimized if the electricity is generated from renewable sources such as wind and solar. On the other hand, there are some drawbacks of these vehicles such as charging time being very long and the mileage range of vehicles not at the desired level. Battery cells are being charged at relatively high C-rates to eliminate these problems, yet high current rates accelerate the aging of batteries and capacity losses due to the generated heat. Generated heat causes overheating, and excess temperature triggers degradation and thermal runaway risks. This paper uncovers how the battery pack temperature uniformity and strict thermal control can be achieved with heat transfer enhancement by conduction (cold plates) and convection (vascular channels). We aimed to reduce the energy consumption of the EV battery pack system while increasing the thermal performance. The impact of the thermal contact resistance is also considered for many realistic scenarios. The results indicate that an integrated system with cold plates and vascular channels satisfies the temperature uniformity requirement (over 81%) with comparatively less pumping power (∼72%) of advanced electric vehicles for relatively high C-rates. Furthermore, findings show the temperature level can increase up to 4°C as thermal contact resistance increases. The proposed cooling technique, which has low cost, easy application, and lower energy consumption superiorities, can be implemented in palpable EV battery packs. © 2022 Wiley Periodicals LLC. |
Gungor, S; Cetkin, E; Lorente, S Thermal and electrical characterization of an electric vehicle battery cell, an experimental investigation Journal Article Applied Thermal Engineering, 212 , 2022. @article{Gungor2022b, title = {Thermal and electrical characterization of an electric vehicle battery cell, an experimental investigation}, author = {S Gungor and E Cetkin and S Lorente}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85129534427&doi=10.1016%2fj.applthermaleng.2022.118530&partnerID=40&md5=fe9a51259b3473a5b8a99fc67ed0043c}, doi = {10.1016/j.applthermaleng.2022.118530}, year = {2022}, date = {2022-01-01}, journal = {Applied Thermal Engineering}, volume = {212}, abstract = {This paper documents the experimental characterization of a Li-ion battery cell during charging/discharging cyclic operations. The study of the battery cell is conducted in the absence of cooling aid system, and provides thermal and electrical insights. After describing the experimental set-up, the changes in temperature are presented and highlight the nonuniform distribution of the temperature on the battery cell surface. The findings indicate that the maximum temperature difference on the investigated battery cell surface may reach up to 11 C at 3C and 17 ⁰C at 5C, at the end of the discharge in the natural convection case. These changes in space come with temporal variations that are also documented. Voltage curves are provided during charging and discharging operations. The impact of the discharge rate, ambient temperature are then investigated together with the capacity fade after 500 cycles, and results showed that ventilation and low ambient temperatures allow to alleviate the battery capacity fade by 3%. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } This paper documents the experimental characterization of a Li-ion battery cell during charging/discharging cyclic operations. The study of the battery cell is conducted in the absence of cooling aid system, and provides thermal and electrical insights. After describing the experimental set-up, the changes in temperature are presented and highlight the nonuniform distribution of the temperature on the battery cell surface. The findings indicate that the maximum temperature difference on the investigated battery cell surface may reach up to 11 C at 3C and 17 ⁰C at 5C, at the end of the discharge in the natural convection case. These changes in space come with temporal variations that are also documented. Voltage curves are provided during charging and discharging operations. The impact of the discharge rate, ambient temperature are then investigated together with the capacity fade after 500 cycles, and results showed that ventilation and low ambient temperatures allow to alleviate the battery capacity fade by 3%. © 2022 Elsevier Ltd |
Demirkıran, İ G; Rocha, L A O; Cetkin, E Emergence of asymmetric straight and branched fins in horizontally oriented latent heat thermal energy storage units Journal Article International Journal of Heat and Mass Transfer, 189 , 2022. @article{Demirkıran2022, title = {Emergence of asymmetric straight and branched fins in horizontally oriented latent heat thermal energy storage units}, author = {İ G Demirkıran and L A O Rocha and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85125777922&doi=10.1016%2fj.ijheatmasstransfer.2022.122726&partnerID=40&md5=dfad7a7519437326f78acb3461cbaa3d}, doi = {10.1016/j.ijheatmasstransfer.2022.122726}, year = {2022}, date = {2022-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {189}, abstract = {Mobilized thermal energy storage units have a vital role in reducing energy consumption in buildings by enabling industrial waste heat to be used in buildings. High conductive fins can enhance the heat transfer performance of mobilized thermal energy storage tanks which suffer significantly from the low thermal conductivity of phase change materials. On the other hand, investment costs of the mobilized thermal energy storage tanks need to be decreased to compete with fossil fuel-driven systems in buildings. The present study numerically investigates the effect of innovative fin structures on the melting performance for fixed fin material volume to disable cost increase. Two-dimensional models with phase change were simulated for shell-and-tube heat exchangers. The shell geometry was designed sufficiently large to observe the melting growth of phase change material independent from shell walls within the given charging time. Straight and Branched type fin structures with the fin numbers of Nfin=2, 4, and 6 were simulated to uncover the effect of shape and length scale of fins on natural convection-driven melting. It was found that Straight fin type is more suited than Branched fins as they do not show significant melting enhancement with increased complexity and cost. The fin structures in all cases performed better when located at the top of the heat transfer fluid tube, even though the literature considers that top-located fins inhibit natural convection circulations. Varying the number of fins from (2-fin) to (4-fin) causes 15.8% increase in melting ratio, but further increase in the fin number (6-fin) reduces melting ratio below the (4-fin) case. Within (4-fin) structures located at the top, using distinct fin lengths yields melting ratio to increase 28.1%. Overall, the results show that heat transfer could be improved by varying the fin structure without increasing total fin volume and cost. The melting region growth shape with optimized fin structure forms the basis for the multitube arrangement of mobilized thermal energy storage units to enhance heat transfer performance with low cost. © 2022 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mobilized thermal energy storage units have a vital role in reducing energy consumption in buildings by enabling industrial waste heat to be used in buildings. High conductive fins can enhance the heat transfer performance of mobilized thermal energy storage tanks which suffer significantly from the low thermal conductivity of phase change materials. On the other hand, investment costs of the mobilized thermal energy storage tanks need to be decreased to compete with fossil fuel-driven systems in buildings. The present study numerically investigates the effect of innovative fin structures on the melting performance for fixed fin material volume to disable cost increase. Two-dimensional models with phase change were simulated for shell-and-tube heat exchangers. The shell geometry was designed sufficiently large to observe the melting growth of phase change material independent from shell walls within the given charging time. Straight and Branched type fin structures with the fin numbers of Nfin=2, 4, and 6 were simulated to uncover the effect of shape and length scale of fins on natural convection-driven melting. It was found that Straight fin type is more suited than Branched fins as they do not show significant melting enhancement with increased complexity and cost. The fin structures in all cases performed better when located at the top of the heat transfer fluid tube, even though the literature considers that top-located fins inhibit natural convection circulations. Varying the number of fins from (2-fin) to (4-fin) causes 15.8% increase in melting ratio, but further increase in the fin number (6-fin) reduces melting ratio below the (4-fin) case. Within (4-fin) structures located at the top, using distinct fin lengths yields melting ratio to increase 28.1%. Overall, the results show that heat transfer could be improved by varying the fin structure without increasing total fin volume and cost. The melting region growth shape with optimized fin structure forms the basis for the multitube arrangement of mobilized thermal energy storage units to enhance heat transfer performance with low cost. © 2022 Elsevier Ltd |
Demirkıran, İ G; Cetkin, E Computation time reduction of PCM melting process by changing modeling parameters Journal Article Numerical Heat Transfer; Part A: Applications, 83 (1), pp. 50-67, 2022. @article{Demirkıran202250, title = {Computation time reduction of PCM melting process by changing modeling parameters}, author = {İ G Demirkıran and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85142904241&doi=10.1080%2f10407782.2022.2149229&partnerID=40&md5=9060437b1c078c4230068c898ce0213f}, doi = {10.1080/10407782.2022.2149229}, year = {2022}, date = {2022-01-01}, journal = {Numerical Heat Transfer; Part A: Applications}, volume = {83}, number = {1}, pages = {50-67}, abstract = {This study can be considered as a helpful reference for whom endeavor to boost the computation efficiency of the PCM melting process. Researchers sacrifice accuracy to decrease computation time since computational fluid dynamics (CFD) solutions of PCM melting processes require comparatively very long time, i.e., from hours to days or weeks, depending on the system geometry. The present study compares the approaches recommended in the literature in terms of their influence on computation time reduction and accuracy. A horizontally finned tube LHTES unit is modeled in 2-D space using ANSYS Fluent, the most common commercial CFD software for the considered problem in the literature. The outcomes obtained from the attempts to boost the computation efficiency are as follows: adaptive time step size approach causes 72% enhancement in computation time (from 90 hours to 25 hours), frozen flux algorithm and constant thermophysical properties have almost no influence on computation time. Even though low convergence criteria and neglecting natural convection reduces computation time drastically, the errors in accuracy are not in acceptable level. © 2022 Taylor & Francis Group, LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study can be considered as a helpful reference for whom endeavor to boost the computation efficiency of the PCM melting process. Researchers sacrifice accuracy to decrease computation time since computational fluid dynamics (CFD) solutions of PCM melting processes require comparatively very long time, i.e., from hours to days or weeks, depending on the system geometry. The present study compares the approaches recommended in the literature in terms of their influence on computation time reduction and accuracy. A horizontally finned tube LHTES unit is modeled in 2-D space using ANSYS Fluent, the most common commercial CFD software for the considered problem in the literature. The outcomes obtained from the attempts to boost the computation efficiency are as follows: adaptive time step size approach causes 72% enhancement in computation time (from 90 hours to 25 hours), frozen flux algorithm and constant thermophysical properties have almost no influence on computation time. Even though low convergence criteria and neglecting natural convection reduces computation time drastically, the errors in accuracy are not in acceptable level. © 2022 Taylor & Francis Group, LLC. |
Gocmen, S; Cetkin, E Emergence of elevated battery positioning in air cooled battery packs for temperature uniformity in ultra-fast dis/charging applications Journal Article Journal of Energy Storage, 45 , 2022. @article{Gocmen2022, title = {Emergence of elevated battery positioning in air cooled battery packs for temperature uniformity in ultra-fast dis/charging applications}, author = {S Gocmen and E Cetkin}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85118748009&doi=10.1016%2fj.est.2021.103516&partnerID=40&md5=736e4f4ff2d5aeb573d8473e4039ed23}, doi = {10.1016/j.est.2021.103516}, year = {2022}, date = {2022-01-01}, journal = {Journal of Energy Storage}, volume = {45}, abstract = {Pure electric vehicles (EVs) are gradually becoming major interest of research in worldwide. Battery cells in EV battery packs must be kept in between the desired operational temperature range (∼30°C) and temperature should be homogeneous in packs to eliminate safety risks and prolong battery life. In this study, performance of a novel BTMS design was studied at various discharge conditions with fast and ultra-fast C-rate values. Cooling with natural convection exceeds desired operational temperature in the pack as well as forced air convection in Z-type manifold. Elevated battery positions yield flow resistance along the air channels in between battery cells to be uniform which yields flow rate sweeping the surface of each cell to be the same. Therefore, the maximum temperature in between cells decreases to less than 0.3K from the order of 12K. The temperature uniformity is essential for ageing and electrical resistance of cells to be homogeneous in a pack. In addition, heat transfer enhancement with various fin designs is documented as well as its effect on the temperature distribution. The accuracy of numerical studies is validated by experimental work. The results show that the peak temperature can be kept under the desired operational temperature with minimum deviation in the temperature difference for distinct operation conditions required for advanced electric vehicles (cars, airplanes, helicopters) with extreme charging and discharging capability. © 2021 Elsevier Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Pure electric vehicles (EVs) are gradually becoming major interest of research in worldwide. Battery cells in EV battery packs must be kept in between the desired operational temperature range (∼30°C) and temperature should be homogeneous in packs to eliminate safety risks and prolong battery life. In this study, performance of a novel BTMS design was studied at various discharge conditions with fast and ultra-fast C-rate values. Cooling with natural convection exceeds desired operational temperature in the pack as well as forced air convection in Z-type manifold. Elevated battery positions yield flow resistance along the air channels in between battery cells to be uniform which yields flow rate sweeping the surface of each cell to be the same. Therefore, the maximum temperature in between cells decreases to less than 0.3K from the order of 12K. The temperature uniformity is essential for ageing and electrical resistance of cells to be homogeneous in a pack. In addition, heat transfer enhancement with various fin designs is documented as well as its effect on the temperature distribution. The accuracy of numerical studies is validated by experimental work. The results show that the peak temperature can be kept under the desired operational temperature with minimum deviation in the temperature difference for distinct operation conditions required for advanced electric vehicles (cars, airplanes, helicopters) with extreme charging and discharging capability. © 2021 Elsevier Ltd |
Gungor, S; Cetkin, E; Lorente, S Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach Journal Article International Journal of Heat and Mass Transfer, 182 , 2022. @article{Gungor2022c, title = {Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach}, author = {S Gungor and E Cetkin and S Lorente}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85114670203&doi=10.1016%2fj.ijheatmasstransfer.2021.121918&partnerID=40&md5=705da93dfe3b91f9ec006e9534aa4333}, doi = {10.1016/j.ijheatmasstransfer.2021.121918}, year = {2022}, date = {2022-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {182}, abstract = {With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. © 2021}, keywords = {}, pubstate = {published}, tppubtype = {article} } With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate. © 2021 |
Ulu, A; Yildiz, G; Rodriguez, A D; Özkol, Ü Spray Analysis of Biodiesels Derived from Various Biomass Resources in a Constant Volume Spray Chamber Journal Article ACS Omega, 7 (23), pp. 19365-19379, 2022. @article{Ulu202219365, title = {Spray Analysis of Biodiesels Derived from Various Biomass Resources in a Constant Volume Spray Chamber}, author = {A Ulu and G Yildiz and A D Rodriguez and Ü Özkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85132107803&doi=10.1021%2facsomega.2c00952&partnerID=40&md5=995ab045ec0310695a47b69c61b69c80}, doi = {10.1021/acsomega.2c00952}, year = {2022}, date = {2022-01-01}, journal = {ACS Omega}, volume = {7}, number = {23}, pages = {19365-19379}, abstract = {This research aimed to analyze the spray characteristics of various biodiesels, which have rarely been investigated in terms of spray analysis in the literature compared to fossil diesel. For this purpose, four different methyl ester-type biodiesels were produced from canola, corn, cottonseed, and sunflower oils. These feedstocks were selected due to their wide availability in Turkey and being among the significant resources for biodiesel production. Measured physical properties of biodiesel samples showed that biodiesel fuels had, on average, 1.7 to 1.9 times higher viscosities, 5.3 to 6.6% larger densities, and 37 to 39.1% higher contact angle values than the reference diesel fuel. Spray characteristics of all fuels were experimentally examined in a constant volume spray chamber under chamber pressures of 0, 5, 10, and 15 bar and injection pressures of 600, 800, and 1000 bar. All tested biodiesels performed, on average, 3 to 20% longer spray penetration lengths, 5 to 30% narrower spray cone angles, and 5-18% lesser spray areas than the reference diesel fuel under chamber pressures of 5 and 10 bar. No significant differences occurred at 15 bar ambient pressure between biodiesels and diesel. In addition, analytical and empirical predictions showed that biodiesels had around 21.2-35.1% larger SMD values and approximately 7% lower air entrainment. © 2022 American Chemical Society. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This research aimed to analyze the spray characteristics of various biodiesels, which have rarely been investigated in terms of spray analysis in the literature compared to fossil diesel. For this purpose, four different methyl ester-type biodiesels were produced from canola, corn, cottonseed, and sunflower oils. These feedstocks were selected due to their wide availability in Turkey and being among the significant resources for biodiesel production. Measured physical properties of biodiesel samples showed that biodiesel fuels had, on average, 1.7 to 1.9 times higher viscosities, 5.3 to 6.6% larger densities, and 37 to 39.1% higher contact angle values than the reference diesel fuel. Spray characteristics of all fuels were experimentally examined in a constant volume spray chamber under chamber pressures of 0, 5, 10, and 15 bar and injection pressures of 600, 800, and 1000 bar. All tested biodiesels performed, on average, 3 to 20% longer spray penetration lengths, 5 to 30% narrower spray cone angles, and 5-18% lesser spray areas than the reference diesel fuel under chamber pressures of 5 and 10 bar. No significant differences occurred at 15 bar ambient pressure between biodiesels and diesel. In addition, analytical and empirical predictions showed that biodiesels had around 21.2-35.1% larger SMD values and approximately 7% lower air entrainment. © 2022 American Chemical Society. All rights reserved. |
Ulu, A; Yildiz, G; Özkol, Ü; Rodriguez, A D Experimental investigation of spray characteristics of ethyl esters in a constant volume chamber Journal Article Biomass Conversion and Biorefinery, 2022. @article{Ulu2022b, title = {Experimental investigation of spray characteristics of ethyl esters in a constant volume chamber}, author = {A Ulu and G Yildiz and Ü Özkol and A D Rodriguez}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85125134221&doi=10.1007%2fs13399-022-02476-3&partnerID=40&md5=f56d167f075688de07dc30653fa40c64}, doi = {10.1007/s13399-022-02476-3}, year = {2022}, date = {2022-01-01}, journal = {Biomass Conversion and Biorefinery}, abstract = {Abstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Abstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature. |
Esenoğlu, G; Barisik, M; Tanoğlu, M; Yeke, M; Türkdoğan, C; İplikçi, H; Martin, S; Nuhoğlu, K; Aktaş, E; Dehneliler, S; İriş, M E Improving adhesive behavior of fiber reinforced composites by incorporating electrospun Polyamide-6,6 nanofibers in joining region Journal Article Journal of Composite Materials, 56 (29), pp. 4449-4459, 2022. @article{Esenoğlu20224449, title = {Improving adhesive behavior of fiber reinforced composites by incorporating electrospun Polyamide-6,6 nanofibers in joining region}, author = {G Esenoğlu and M Barisik and M Tanoğlu and M Yeke and C Türkdoğan and H İplikçi and S Martin and K Nuhoğlu and E Aktaş and S Dehneliler and M E İriş}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85139985112&doi=10.1177%2f00219983221133478&partnerID=40&md5=699a47f9c6bc7948245cdc6f370c483e}, doi = {10.1177/00219983221133478}, year = {2022}, date = {2022-01-01}, journal = {Journal of Composite Materials}, volume = {56}, number = {29}, pages = {4449-4459}, abstract = {Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 ± 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially. © The Author(s) 2022.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 ± 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially. © The Author(s) 2022. |
2021 |
Cetkin, E; Miguel, A F Asymmetric Y-shaped Micromixers with Spherical Mixing Chamber for Enhanced Mixing Efficiency and Reduced Flow Impedance Journal Article JOURNAL OF APPLIED FLUID MECHANICS, 14 (5), pp. 1389-1397, 2021. @article{WOS:000658420100009, title = {Asymmetric Y-shaped Micromixers with Spherical Mixing Chamber for Enhanced Mixing Efficiency and Reduced Flow Impedance}, author = {E Cetkin and A F Miguel}, doi = {10.47176/jafm.14.05.32317}, year = {2021}, date = {2021-09-01}, journal = {JOURNAL OF APPLIED FLUID MECHANICS}, volume = {14}, number = {5}, pages = {1389-1397}, abstract = {Microfluidic devices have many attractive qualities such as low cost, small size, and in-field use. Micromixers are very important components of these devices because affect their efficiency. In a passive mixer, the structural characteristics of the mixer are crucial and must be analyzed. This paper presents a numerical study of the mixing in passive Y-shaped micromixers with a spherical mixing chamber for a volume constrained system. The effect of asymmetric bifurcated ducts, the angle in between the inflow ducts, eccentricity and, obstacles inserted in the mixing sphere, on the mixing efficiency and flow impedance is evaluated. Vortical structures characteristics and the possible occurrence of engulfment are also identified. The results show that flow impedance (pressure drop for unit volumetric flow rate) can be decreased greatly for the same mixing efficiency as the volume of the spherical mixing chamber is 20% of the total volume. Insertion of the obstacles into the sphere mixing chamber decreases the mixing efficiency while they increase the flow impedance. The results also show that spherical mixing chamber enhances mixing efficiency while decreasing flow impedance if the volume reserved for it is greater than a limit value which depends on the diameter and length scale ratios in between the mother and daughter ducts as well as the total volume. Overall, the paper documents the variation of mixing efficiency and flow impedance based on the geometrical parameters of three-dimensional asymmetric passive micromixer with sphere mixing chamber.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Microfluidic devices have many attractive qualities such as low cost, small size, and in-field use. Micromixers are very important components of these devices because affect their efficiency. In a passive mixer, the structural characteristics of the mixer are crucial and must be analyzed. This paper presents a numerical study of the mixing in passive Y-shaped micromixers with a spherical mixing chamber for a volume constrained system. The effect of asymmetric bifurcated ducts, the angle in between the inflow ducts, eccentricity and, obstacles inserted in the mixing sphere, on the mixing efficiency and flow impedance is evaluated. Vortical structures characteristics and the possible occurrence of engulfment are also identified. The results show that flow impedance (pressure drop for unit volumetric flow rate) can be decreased greatly for the same mixing efficiency as the volume of the spherical mixing chamber is 20% of the total volume. Insertion of the obstacles into the sphere mixing chamber decreases the mixing efficiency while they increase the flow impedance. The results also show that spherical mixing chamber enhances mixing efficiency while decreasing flow impedance if the volume reserved for it is greater than a limit value which depends on the diameter and length scale ratios in between the mother and daughter ducts as well as the total volume. Overall, the paper documents the variation of mixing efficiency and flow impedance based on the geometrical parameters of three-dimensional asymmetric passive micromixer with sphere mixing chamber. |
Demirkiran, Ismail Gurkan; Cetkin, Erdal Emergence of rectangular shell shape in thermal energy storage applications: Fitting melted phase changing material in a fixed space Journal Article JOURNAL OF ENERGY STORAGE, 37 , 2021. @article{WOS:000641410200002, title = {Emergence of rectangular shell shape in thermal energy storage applications: Fitting melted phase changing material in a fixed space}, author = {Ismail Gurkan Demirkiran and Erdal Cetkin}, doi = {10.1016/j.est.2021.102455}, year = {2021}, date = {2021-05-01}, journal = {JOURNAL OF ENERGY STORAGE}, volume = {37}, abstract = {Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we document the effect of heat transfer fluid (HTF) tube position and shell shape on the melting time and sensible energy requirement for melting a phase change material (PCM) in a multitube latent heat thermal energy storage (LHTES) application. Tube location and shell shape are essential as the shape of the melted region, i.e. similar to the boundary layer, affects convective heat transfer performance. HTF tube total area is fixed in all cases to have the same amount of PCM. In order to eliminate the effect of heat transfer surface area variation, results of two- and four-tube configurations were compared within themselves. Liquid fraction, sensible enthalpy content, and latent/sensible enthalpy ratio relative to time were documented for two and four HTF configurations in various shell shape and tube locations. Results show that eccentric two tubes with rectangular shell decreases melting time and sensible energy requirement from 67 min to 32 min and from 161.8 kJ/kg to 136.3 kJ/kg for 72.3% liquid fraction, respectively, in comparison to the concentric tubes with the circular shell. When the number of HTF tubes increases to four, then the required melting time and sensible energy decrease 80% and 3.8%, respectively, for PCM to melt completely as the concentric tubes and circular shell is replaced with eccentric tubes and rectangular shell. Results of liquid fraction variation relative to time show that S-curve of melting becomes steeper if PCM distribution is such that the intersection of melted regions is delayed. Therefore, melted PCM regions could be packed into a shell that minimizes melting time and required sensible energy. Even rectangular shell shape increases the heat transfer surface (increased heat loss rate) because melting time has decreased greatly, total energy lost to the ambient from the surfaces of shell decreases. Eccentricity slows down the solidification process but due to increased heat loss rate from the surface, rectangular shell enables faster solidification than circular shell shape. There is a trade off in between solidification time and heat loss energy for rectangular channels which can be optimized by selecting proper insulation thickness. Overall, the results show that without any thermal conductivity enhancement (TCE) method, melting performance and latent heat storage capability can be significantly enhanced as decreasing the sensible heat storage by fitting the melted PCM regions into a fixed space for the applications where charging speed is lot faster than discharging. |
Alan, B O; Barisik, M Size and roughness dependent temperature effects on surface charge of silica nanoparticles Journal Article Colloids and Surfaces A: Physicochemical and Engineering Aspects, 629 , 2021. @article{Alan2021, title = {Size and roughness dependent temperature effects on surface charge of silica nanoparticles}, author = {B O Alan and M Barisik}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85113802606&doi=10.1016%2fj.colsurfa.2021.127407&partnerID=40&md5=88470bff4bf146cfb5c2054495edf0c1}, doi = {10.1016/j.colsurfa.2021.127407}, year = {2021}, date = {2021-01-01}, journal = {Colloids and Surfaces A: Physicochemical and Engineering Aspects}, volume = {629}, abstract = {Silica nanoparticles (SNP) with different sizes and surface areas are used in numerous micro/nanofluidic applications, while their surface charge properties play a major role in their function. In many of these applications, SNPs also undergo temperature variation. We present that an increase in temperature yields a substantial increase in SNP surface charge depending on nanoparticle size and surface roughness, which cannot be estimated by existing theory. As a continuation of our earlier work characterizing the deviation of SNP surface charging from theoretical predictions due to curvature and EDL overlap effects, this study presents the differentiation from the theory in temperature dependence under various conditions. As we calculate surface chemistry as a function of local ionic conditions (Charge Regulation), temperature variation changed the equilibrium constants of protonation/deprotonation reactions of the SNP surface, in addition to changes occurring in relative permittivity and ionic mobilities. Results show that variation of SNP surface charge by temperature decreases by decreasing particle size and/or increasing roughness size, compare to theoretical flat plate calculations considering similar temperature-dependent properties and charge regulation on the surface. We characterized these deviations by obtaining an “electrokinetic similarity” between different systems of various size and roughness at various ionic conditions based on the non-dimensional groups of λ/DP and λ/DR. Based on these, we devised a phenomenological model as an extension to the flat plate theory to successfully predict the surface charge of SNPs as a function of the particle size, roughness size, and temperature. The current findings are important for the characterization of SNPs through temperature variations and can also be used to adjust the surface charge of SNPs by tuning the temperature. © 2021 Elsevier B.V.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Silica nanoparticles (SNP) with different sizes and surface areas are used in numerous micro/nanofluidic applications, while their surface charge properties play a major role in their function. In many of these applications, SNPs also undergo temperature variation. We present that an increase in temperature yields a substantial increase in SNP surface charge depending on nanoparticle size and surface roughness, which cannot be estimated by existing theory. As a continuation of our earlier work characterizing the deviation of SNP surface charging from theoretical predictions due to curvature and EDL overlap effects, this study presents the differentiation from the theory in temperature dependence under various conditions. As we calculate surface chemistry as a function of local ionic conditions (Charge Regulation), temperature variation changed the equilibrium constants of protonation/deprotonation reactions of the SNP surface, in addition to changes occurring in relative permittivity and ionic mobilities. Results show that variation of SNP surface charge by temperature decreases by decreasing particle size and/or increasing roughness size, compare to theoretical flat plate calculations considering similar temperature-dependent properties and charge regulation on the surface. We characterized these deviations by obtaining an “electrokinetic similarity” between different systems of various size and roughness at various ionic conditions based on the non-dimensional groups of λ/DP and λ/DR. Based on these, we devised a phenomenological model as an extension to the flat plate theory to successfully predict the surface charge of SNPs as a function of the particle size, roughness size, and temperature. The current findings are important for the characterization of SNPs through temperature variations and can also be used to adjust the surface charge of SNPs by tuning the temperature. © 2021 Elsevier B.V. |
Yenigun, O; Barisik, M Local Heat Transfer Control using Liquid Dielectrophoresis at Graphene/Water Interfaces Journal Article International Journal of Heat and Mass Transfer, 166 , 2021. @article{Yenigun2021, title = {Local Heat Transfer Control using Liquid Dielectrophoresis at Graphene/Water Interfaces}, author = {O Yenigun and M Barisik}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85097790790&doi=10.1016%2fj.ijheatmasstransfer.2020.120801&partnerID=40&md5=e8754da2dd49beb00b7eb1432717ea55}, doi = {10.1016/j.ijheatmasstransfer.2020.120801}, year = {2021}, date = {2021-01-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {166}, abstract = {Graphene-based materials are considered for the solution of the thermal management problem of current and next generation micro/nano-electronics with high heat generation densities. However, the hydrophobic nature of few-layer graphene makes passing heat to a fluid very challenging. We introduced an active and local manipulation of heat transfer between graphene and water using an applied, non-uniform electric field. When water undergoes electric field induced orientation polarization and liquid dielectrophoresis, a substantial increase in heat transfer develops due to a decrease in interfacial thermal resistance and increase in thermal conductivity. By using two locally embedded pin and plate electrodes of different sizes, we demonstrated a two-dimensional heat transfer control between two parallel few-layer graphene slabs. We obtained local heat transfer increase up to nine times at pin electrode region with an ultra-low Kapitza resistance through the studied non-uniform electric field strength range creating highly-ordered compressed water in the experimentally measured density limits. With this technique, heat can be (i) distributed from a smaller location to a larger section and/or (ii) collected to a smaller section from a larger region. Current results are important for hot spot cooling and/or heat focusing applications. © 2020}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene-based materials are considered for the solution of the thermal management problem of current and next generation micro/nano-electronics with high heat generation densities. However, the hydrophobic nature of few-layer graphene makes passing heat to a fluid very challenging. We introduced an active and local manipulation of heat transfer between graphene and water using an applied, non-uniform electric field. When water undergoes electric field induced orientation polarization and liquid dielectrophoresis, a substantial increase in heat transfer develops due to a decrease in interfacial thermal resistance and increase in thermal conductivity. By using two locally embedded pin and plate electrodes of different sizes, we demonstrated a two-dimensional heat transfer control between two parallel few-layer graphene slabs. We obtained local heat transfer increase up to nine times at pin electrode region with an ultra-low Kapitza resistance through the studied non-uniform electric field strength range creating highly-ordered compressed water in the experimentally measured density limits. With this technique, heat can be (i) distributed from a smaller location to a larger section and/or (ii) collected to a smaller section from a larger region. Current results are important for hot spot cooling and/or heat focusing applications. © 2020 |
Sarialtin, H; Geyer, R; Zafer, C Environmental assessment of transparent conductive oxide-free efficient flexible organo-lead halide perovskite solar cell Journal Article Energy Sources, Part A: Recovery, Utilization and Environmental Effects, 43 (20), pp. 2544-2553, 2021. @article{Sarialtin20212544, title = {Environmental assessment of transparent conductive oxide-free efficient flexible organo-lead halide perovskite solar cell}, author = {H Sarialtin and R Geyer and C Zafer}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85095721962&doi=10.1080%2f15567036.2020.1842560&partnerID=40&md5=fce22be696576207a0d582736c5feda1}, doi = {10.1080/15567036.2020.1842560}, year = {2021}, date = {2021-01-01}, journal = {Energy Sources, Part A: Recovery, Utilization and Environmental Effects}, volume = {43}, number = {20}, pages = {2544-2553}, abstract = {Perovskite solar cells (PSCs), one of the third-generation photovoltaic (PV) technologies, have recently become a very popular topic in photovoltaic research. This technology, which is a candidate for commercialization in the future, needs to be evaluated from an environmental point of view. The amount of electricity consumption is the most important factor that directly determines the environmental impact values of photovoltaic cell manufacturing. Transparent conductive oxide (TCO) coated glass is one of the major contributors to electricity consumption in PSC architecture. It is therefore useful to investigate the environmental profile of TCO coated glass-free PSC architecture with conventional PVs. One of the solutions to this issue is manufacturing PSC on a flexible substrate. Flexible PVs are considered to be one of the most promising candidates for mass production with its advantages of low-temperature manufacturing, higher efficiency with a lower weight, portability, and compatibility with a roll to roll fabrication. In this work, we show that the environmental impacts of a representative PSCs with a flexible substrate. While the energy payback time (EPBT) of the flexible PSC is already competitive with commercial PVs, the device must reach a 25-year cell lifetime for its global warming potential (GWP) to reach a reasonable range. © 2020 Taylor & Francis Group, LLC.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Perovskite solar cells (PSCs), one of the third-generation photovoltaic (PV) technologies, have recently become a very popular topic in photovoltaic research. This technology, which is a candidate for commercialization in the future, needs to be evaluated from an environmental point of view. The amount of electricity consumption is the most important factor that directly determines the environmental impact values of photovoltaic cell manufacturing. Transparent conductive oxide (TCO) coated glass is one of the major contributors to electricity consumption in PSC architecture. It is therefore useful to investigate the environmental profile of TCO coated glass-free PSC architecture with conventional PVs. One of the solutions to this issue is manufacturing PSC on a flexible substrate. Flexible PVs are considered to be one of the most promising candidates for mass production with its advantages of low-temperature manufacturing, higher efficiency with a lower weight, portability, and compatibility with a roll to roll fabrication. In this work, we show that the environmental impacts of a representative PSCs with a flexible substrate. While the energy payback time (EPBT) of the flexible PSC is already competitive with commercial PVs, the device must reach a 25-year cell lifetime for its global warming potential (GWP) to reach a reasonable range. © 2020 Taylor & Francis Group, LLC. |
2020 |
Coskun, Turgay; Cetkin, Erdal A review of heat and fluid flow characteristics in microchannel heat sinks Journal Article HEAT TRANSFER, 49 (8), pp. 4109-4133, 2020, ISSN: 2688-4534. @article{ISI:000595699600002, title = {A review of heat and fluid flow characteristics in microchannel heat sinks}, author = {Turgay Coskun and Erdal Cetkin}, doi = {10.1002/htj.21819}, issn = {2688-4534}, year = {2020}, date = {2020-12-01}, journal = {HEAT TRANSFER}, volume = {49}, number = {8}, pages = {4109-4133}, abstract = {Heat transfer and flow characteristic in microchannel heat sinks (MCHS) are extensively studied in the literature due to high heat transfer rate capability by increased heat transfer surface area relative to the macroscale heat sinks. However, heat transfer and fluid flow characteristics in MCHS differ from conventional ones because of the scaling effects. This review summarizes the studies that are mainly based on heat transfer and fluid flow characteristic in MCHS. There is no consistency among the published results; however, everyone agrees on that there is no new physical phenomenon in microscale that does not exist at macroscale. Only difference between them is that the effect of some physical phenomena such as viscous dissipation, axial heat conduction, entrance effect, rarefaction, and so forth, is negligibly small at macroscale, whereas it is not at microscale. The effect of these physical phenomena on the heat transfer and flow characteristics becomes significant with respect to specified conditions such as Reynolds number, Peclet number, hydraulic diameter, and heat transfer boundary conditions. Here, the literature was reviewed to document when these physical phenomena become significant and insignificant.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Heat transfer and flow characteristic in microchannel heat sinks (MCHS) are extensively studied in the literature due to high heat transfer rate capability by increased heat transfer surface area relative to the macroscale heat sinks. However, heat transfer and fluid flow characteristics in MCHS differ from conventional ones because of the scaling effects. This review summarizes the studies that are mainly based on heat transfer and fluid flow characteristic in MCHS. There is no consistency among the published results; however, everyone agrees on that there is no new physical phenomenon in microscale that does not exist at macroscale. Only difference between them is that the effect of some physical phenomena such as viscous dissipation, axial heat conduction, entrance effect, rarefaction, and so forth, is negligibly small at macroscale, whereas it is not at microscale. The effect of these physical phenomena on the heat transfer and flow characteristics becomes significant with respect to specified conditions such as Reynolds number, Peclet number, hydraulic diameter, and heat transfer boundary conditions. Here, the literature was reviewed to document when these physical phenomena become significant and insignificant. |
Toprak, Kasim; Ouedraogo, Kiswendsida Elias Performance Analysis of Thermal Storage Assisted Cooling Tower with Night Cooling Journal Article JOURNAL OF POLYTECHNIC-POLITEKNIK DERGISI, 23 (4), pp. 1027-1035, 2020, ISSN: 1302-0900. @article{ISI:000581901200009, title = {Performance Analysis of Thermal Storage Assisted Cooling Tower with Night Cooling}, author = {Kasim Toprak and Kiswendsida Elias Ouedraogo}, issn = {1302-0900}, year = {2020}, date = {2020-12-01}, journal = {JOURNAL OF POLYTECHNIC-POLITEKNIK DERGISI}, volume = {23}, number = {4}, pages = {1027-1035}, abstract = {As global warming and water scarcity issues continue to grow, it is essential to increase resources efficiency for air conditioners and power plants. In order to increase the efficiency, the systems need to be modified to take the advantages of the low night temperature and thermal storage tanks. In this study, the low night temperature and thermal storage tanks effects on the cooling tower is studied using TRNSYS. Using a chiller operating from 8:00 to 16:00 as a case study, hot water from the condenser is partially stored on daytime and cooled slowly during the night. The storage tank volume is optimized by considering two big tanks and five small tanks. The results show that night cooling reduces cooling water temperature by 5.8 degrees C or 21.8% while the cooling efficiency is increased by 36%. The thermal storage tanks enable to have the low continuous flow rate and help to reduce the fan power by 67.1%. On the storage side, compared to two tanks system, the tanks volume is reduced by 16.5% when 5 tanks are used. In theory this reduction can go up to 50% by increasing the number of tanks and reducing their individual size.}, keywords = {}, pubstate = {published}, tppubtype = {article} } As global warming and water scarcity issues continue to grow, it is essential to increase resources efficiency for air conditioners and power plants. In order to increase the efficiency, the systems need to be modified to take the advantages of the low night temperature and thermal storage tanks. In this study, the low night temperature and thermal storage tanks effects on the cooling tower is studied using TRNSYS. Using a chiller operating from 8:00 to 16:00 as a case study, hot water from the condenser is partially stored on daytime and cooled slowly during the night. The storage tank volume is optimized by considering two big tanks and five small tanks. The results show that night cooling reduces cooling water temperature by 5.8 degrees C or 21.8% while the cooling efficiency is increased by 36%. The thermal storage tanks enable to have the low continuous flow rate and help to reduce the fan power by 67.1%. On the storage side, compared to two tanks system, the tanks volume is reduced by 16.5% when 5 tanks are used. In theory this reduction can go up to 50% by increasing the number of tanks and reducing their individual size. |
Ozcelik, Gokberk H; Satiroglu, Ezgi; Barisik, Murat Size dependent influence of contact line pinning on wetting of nano-textured/patterned silica surfaces Journal Article NANOSCALE, 12 (41), pp. 21376-21391, 2020, ISSN: 2040-3364. @article{ISI:000584907600029, title = {Size dependent influence of contact line pinning on wetting of nano-textured/patterned silica surfaces}, author = {Gokberk H Ozcelik and Ezgi Satiroglu and Murat Barisik}, doi = {10.1039/d0nr05392a}, issn = {2040-3364}, year = {2020}, date = {2020-11-01}, journal = {NANOSCALE}, volume = {12}, number = {41}, pages = {21376-21391}, abstract = {Wetting behavior on a heterogeneous surface undergoes contact angle hysteresis as the droplet stabilized at a metastable state with a contact angle significantly different from its equilibrium value due to contact line pinning. However, there is a lack of consensus on how to calculate the influence of pinning forces. In general, the pinning effect can be characterized as (i) microscopic behavior when a droplet is pinned and the contact angle increases/decreases as the droplet volume increases/decreases and (ii) macroscopic behavior as the pinning effects decrease and ultimately, disappear with the increase of the droplet size. The current work studied both behaviors using molecular dynamics (MD) simulation with more than 300 different size water droplets on silica surfaces with three different patterns across two different wetting conditions. Results showed that the contact angle increases linearly with increasing droplet volume through the microscopic behavior, while the droplet is pinned on top of a certain number of patterns. When we normalized the droplet size with the corresponding pattern size, we observed a ``wetting similarity'' that linear microscopic contact angle variations over different size heterogeneities continuously line up. This shows that the pinning force remains constant and the resulting pinning effects are scalable by the size ratio between the droplet and pattern, independent of the size-scale. The slope of these microscopic linear variations decreases with an increase in the droplet size as observed through the macroscopic behavior. We further found a universal behavior in the variation of the corresponding pinning forces, independent of the wetting condition. In macroscopic behavior, pinning effects become negligible and the contact angle reaches the equilibrium value of the corresponding surface when the diameter of the free-standing droplet is approximately equal to 24 times the size of the surface structure. We found that the pinning effect is scalable with the droplet volume, not the size of the droplet base.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Wetting behavior on a heterogeneous surface undergoes contact angle hysteresis as the droplet stabilized at a metastable state with a contact angle significantly different from its equilibrium value due to contact line pinning. However, there is a lack of consensus on how to calculate the influence of pinning forces. In general, the pinning effect can be characterized as (i) microscopic behavior when a droplet is pinned and the contact angle increases/decreases as the droplet volume increases/decreases and (ii) macroscopic behavior as the pinning effects decrease and ultimately, disappear with the increase of the droplet size. The current work studied both behaviors using molecular dynamics (MD) simulation with more than 300 different size water droplets on silica surfaces with three different patterns across two different wetting conditions. Results showed that the contact angle increases linearly with increasing droplet volume through the microscopic behavior, while the droplet is pinned on top of a certain number of patterns. When we normalized the droplet size with the corresponding pattern size, we observed a ``wetting similarity'' that linear microscopic contact angle variations over different size heterogeneities continuously line up. This shows that the pinning force remains constant and the resulting pinning effects are scalable by the size ratio between the droplet and pattern, independent of the size-scale. The slope of these microscopic linear variations decreases with an increase in the droplet size as observed through the macroscopic behavior. We further found a universal behavior in the variation of the corresponding pinning forces, independent of the wetting condition. In macroscopic behavior, pinning effects become negligible and the contact angle reaches the equilibrium value of the corresponding surface when the diameter of the free-standing droplet is approximately equal to 24 times the size of the surface structure. We found that the pinning effect is scalable with the droplet volume, not the size of the droplet base. |
Yakin, Fetiye Esin; Barisik, Murat; Sen, Tumcan Pore Size and Porosity Dependent Zeta Potentials of Mesoporous Silica Nanoparticles Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 124 (36), pp. 19579-19587, 2020, ISSN: 1932-7447. @article{ISI:000571497000020, title = {Pore Size and Porosity Dependent Zeta Potentials of Mesoporous Silica Nanoparticles}, author = {Fetiye Esin Yakin and Murat Barisik and Tumcan Sen}, doi = {10.1021/acs.jpcc.0c04602}, issn = {1932-7447}, year = {2020}, date = {2020-09-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {124}, number = {36}, pages = {19579-19587}, abstract = {Mesoporous silica nanoparticles (MSNPs) are synthesized in the various forms of porous structures according to an application's needs, while their zeta potentials play a major role in their function. We show that variation in pore size and/or porosity yields a substantial decrease in MSNP zeta potential up to 25% lower than the theoretical zeta potential predictions for a flat surface at the corresponding ionic conditions in moderate pH range. By considering surface chemistry as a function of local ionic conditions (charge regulation), we calculated local zeta potentials around the MSNP which showed variation between pore openings and solid surfaces. Through a systematic study, we evaluated an average three-dimensional zeta potential for MSNPs with various conditions, based on the ratio of the area covered by pore openings to the rest of the MSNP surface area as a function of three-dimensional porosity and pore size. Results show that the high overlap of ionic layers inside the pores creates electric potentials close to zeta potential of the remaining surface, but large pore size and/or high ionic salt concentration yields divergence. We characterized the variation of MSNP zeta potential in terms of porosity (epsilon(3D)), pore size (D-pore), and ionic condition quantified by Debye length (lambda) and obtained unified behavior as a function of the nondimensional group of epsilon(3D)(D-pore/lambda). For epsilon(3D)(D-pore/lambda) < 0.01, MSNP zeta potential remains similar to flat plate predictions, but it decreases by increasing epsilon(3D)(D-pore/lambda) value. The influence of pore entrances on surface zeta potential increases nonlinearly by the increase of porosity and/or decrease of EDL overlap, similar to a change of area to volume ratio. The current findings are important for the understanding and further control of mesoporous particle transport in various promising and groundbreaking applications such as targeted drug delivery.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Mesoporous silica nanoparticles (MSNPs) are synthesized in the various forms of porous structures according to an application's needs, while their zeta potentials play a major role in their function. We show that variation in pore size and/or porosity yields a substantial decrease in MSNP zeta potential up to 25% lower than the theoretical zeta potential predictions for a flat surface at the corresponding ionic conditions in moderate pH range. By considering surface chemistry as a function of local ionic conditions (charge regulation), we calculated local zeta potentials around the MSNP which showed variation between pore openings and solid surfaces. Through a systematic study, we evaluated an average three-dimensional zeta potential for MSNPs with various conditions, based on the ratio of the area covered by pore openings to the rest of the MSNP surface area as a function of three-dimensional porosity and pore size. Results show that the high overlap of ionic layers inside the pores creates electric potentials close to zeta potential of the remaining surface, but large pore size and/or high ionic salt concentration yields divergence. We characterized the variation of MSNP zeta potential in terms of porosity (epsilon(3D)), pore size (D-pore), and ionic condition quantified by Debye length (lambda) and obtained unified behavior as a function of the nondimensional group of epsilon(3D)(D-pore/lambda). For epsilon(3D)(D-pore/lambda) < 0.01, MSNP zeta potential remains similar to flat plate predictions, but it decreases by increasing epsilon(3D)(D-pore/lambda) value. The influence of pore entrances on surface zeta potential increases nonlinearly by the increase of porosity and/or decrease of EDL overlap, similar to a change of area to volume ratio. The current findings are important for the understanding and further control of mesoporous particle transport in various promising and groundbreaking applications such as targeted drug delivery. |
Sen, Tumcan; Barisik, Murat Slip Effects on Ionic Current of Viscoelectric Electroviscous Flows through Different Length Nanofluidic Channels Journal Article LANGMUIR, 36 (31), pp. 9191-9203, 2020, ISSN: 0743-7463. @article{ISI:000562137700018, title = {Slip Effects on Ionic Current of Viscoelectric Electroviscous Flows through Different Length Nanofluidic Channels}, author = {Tumcan Sen and Murat Barisik}, doi = {10.1021/acs.langmuir.0c01457}, issn = {0743-7463}, year = {2020}, date = {2020-08-01}, journal = {LANGMUIR}, volume = {36}, number = {31}, pages = {9191-9203}, abstract = {The pressure driven slip flow of an electrolyte solution is studied through different nanofluidic channel lengths at varying salt concentrations. The viscous-thickening due to the electrostatic interactions within the electric double layer and the reverse ionic transport due to the streaming potential are developed. The influence of the Navier slip boundary condition is described under both electroviscous and viscoelectric effects with a surface charge regulation (CR) model while the observed behavior is compared and validated with molecular dynamic (MD) calculations from multiple studies. Results show that electroviscous and viscoelectric effects decrease transport. Earlier studies at the no slip boundary presented an increase of ionic current by increasing salt concentration and decreasing channel length. In contrast, our study found that the ionic current occurred almost independent of both salt concentration and channel length, except for very short channels and very low salt concentrations, when electroviscous and viscoelectric effects were considered. In the case of the constant slip length condition, ionic conduction was enhanced, but velocity slip developing on surfaces showed significant variation based on the salt concentration and channel length. This is due to the natural CR behavior enhancing the surface charge and consequential near surface electrohydrodynamics as a result of increase in salt concentration and/or decrease of channel length. Considering that the electroviscous effect alone creates up to 70% lower velocity slips than Poiseuille flow predictions, while further including the viscoelectric effect, results in an almost no-slip condition at high salt concentrations and/or short channels. As a result, the ionic current of a viscoelectric electroviscous slip flow is found to be equal to 1/3 of an electroviscous slip flow and to decrease with a decrease in the channel length.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The pressure driven slip flow of an electrolyte solution is studied through different nanofluidic channel lengths at varying salt concentrations. The viscous-thickening due to the electrostatic interactions within the electric double layer and the reverse ionic transport due to the streaming potential are developed. The influence of the Navier slip boundary condition is described under both electroviscous and viscoelectric effects with a surface charge regulation (CR) model while the observed behavior is compared and validated with molecular dynamic (MD) calculations from multiple studies. Results show that electroviscous and viscoelectric effects decrease transport. Earlier studies at the no slip boundary presented an increase of ionic current by increasing salt concentration and decreasing channel length. In contrast, our study found that the ionic current occurred almost independent of both salt concentration and channel length, except for very short channels and very low salt concentrations, when electroviscous and viscoelectric effects were considered. In the case of the constant slip length condition, ionic conduction was enhanced, but velocity slip developing on surfaces showed significant variation based on the salt concentration and channel length. This is due to the natural CR behavior enhancing the surface charge and consequential near surface electrohydrodynamics as a result of increase in salt concentration and/or decrease of channel length. Considering that the electroviscous effect alone creates up to 70% lower velocity slips than Poiseuille flow predictions, while further including the viscoelectric effect, results in an almost no-slip condition at high salt concentrations and/or short channels. As a result, the ionic current of a viscoelectric electroviscous slip flow is found to be equal to 1/3 of an electroviscous slip flow and to decrease with a decrease in the channel length. |
Gocmen, Sinan; Gungor, Sahin; Cetkin, Erdal Thermal management of electric vehicle battery cells with homogeneous coolant and temperature distribution Journal Article JOURNAL OF APPLIED PHYSICS, 127 (23), 2020, ISSN: 0021-8979. @article{ISI:000542961200001, title = {Thermal management of electric vehicle battery cells with homogeneous coolant and temperature distribution}, author = {Sinan Gocmen and Sahin Gungor and Erdal Cetkin}, doi = {10.1063/5.0004453}, issn = {0021-8979}, year = {2020}, date = {2020-06-01}, journal = {JOURNAL OF APPLIED PHYSICS}, volume = {127}, number = {23}, abstract = {Electric vehicles play an integral role in eliminating pollution related to transportation, especially if the electricity is generated via renewable sources. However, storing electricity onboard requires many battery cells. If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway. Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values. However, the current solutions do not yield uniform temperature distribution for all the cells in a pack. Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries. The design process of the developed battery pack begins with a design used in current packs. Later, how the shape of the distributor channel affects flow uniformity is documented. Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity. The design was altered based on a constructal design methodology with an iterative exhaustive search approach. The uncovered constructal design yields a uniform coolant distribution with a maximum of 0.81% flow rate deviation along channels. The developed design is palpable and easy to manufacture relative to the tapered manifold designs. The results also document that the peak temperature difference between the cells decreases from a maximum of 12K to 0.4K. Furthermore, homogenous distribution of air is one of the limiting factors of the development of metal-air batteries. This paper also documents how air can be distributed uniformly to metal-air battery cells in a battery pack.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electric vehicles play an integral role in eliminating pollution related to transportation, especially if the electricity is generated via renewable sources. However, storing electricity onboard requires many battery cells. If the temperature of the cells is not strictly regulated, their capacity decreases in time, and they may burn or explode due to thermal runaway. Battery thermal management systems emerged for safe operations by keeping the battery cell temperatures under limit values. However, the current solutions do not yield uniform temperature distribution for all the cells in a pack. Here, we document that constant temperature distribution can be achieved with uniform coolant distribution to the channels located between batteries. The design process of the developed battery pack begins with a design used in current packs. Later, how the shape of the distributor channel affects flow uniformity is documented. Then, the design complexity was increased to satisfy the flow uniformity condition, which is essential for temperature uniformity. The design was altered based on a constructal design methodology with an iterative exhaustive search approach. The uncovered constructal design yields a uniform coolant distribution with a maximum of 0.81% flow rate deviation along channels. The developed design is palpable and easy to manufacture relative to the tapered manifold designs. The results also document that the peak temperature difference between the cells decreases from a maximum of 12K to 0.4K. Furthermore, homogenous distribution of air is one of the limiting factors of the development of metal-air batteries. This paper also documents how air can be distributed uniformly to metal-air battery cells in a battery pack. |
Alan, Oyku B; Barisik, Murat; Ozcelik, Gokberk H Roughness Effects on the Surface Charge Properties of Silica Nanoparticles Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 124 (13), pp. 7274-7286, 2020, ISSN: 1932-7447. @article{ISI:000526328500032, title = {Roughness Effects on the Surface Charge Properties of Silica Nanoparticles}, author = {Oyku B Alan and Murat Barisik and Gokberk H Ozcelik}, doi = {10.1021/acs.jpcc.0c00120}, issn = {1932-7447}, year = {2020}, date = {2020-04-01}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {124}, number = {13}, pages = {7274-7286}, abstract = {The surface charge property of silica nanoparticles plays a key role in their function. Previous studies assumed surface charge as a homogeneously distributed constant material property, independent of the nanoparticle size and surface condition. Instead, this study considered surface chemistry as a function of local ionic conditions (Charge Regulation) to calculate the local surface charges around a rough nanoparticle, as an extension to our earlier study (J. Phys. Chem. C 2014, 118 (4), 1836-1842). For the current surface heterogeneity in the form of concave and convex circles, the surface charge showed a distinct local variation: decrease due to the electrical double layer (EDL) overlap in the valleys and increase due to curvature effects on the hills of the surface structure. The average of local surface charges decreased with the decrease of the roughness size (D-R), depending on the particle size (D-P) and pH. We characterized the variation of the average surface charge by a nondimensional group we formed as a measure for the EDL overlap and curvature effects [(D-R/lambda) x (D-R/D-P)]. Based on this, we devised a phenomenological model as an extension to the existing flat surface theory, which can successfully predict the average surface charge around a rough/patterned nanoparticle as a function of the particle size, roughness size, and pH.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The surface charge property of silica nanoparticles plays a key role in their function. Previous studies assumed surface charge as a homogeneously distributed constant material property, independent of the nanoparticle size and surface condition. Instead, this study considered surface chemistry as a function of local ionic conditions (Charge Regulation) to calculate the local surface charges around a rough nanoparticle, as an extension to our earlier study (J. Phys. Chem. C 2014, 118 (4), 1836-1842). For the current surface heterogeneity in the form of concave and convex circles, the surface charge showed a distinct local variation: decrease due to the electrical double layer (EDL) overlap in the valleys and increase due to curvature effects on the hills of the surface structure. The average of local surface charges decreased with the decrease of the roughness size (D-R), depending on the particle size (D-P) and pH. We characterized the variation of the average surface charge by a nondimensional group we formed as a measure for the EDL overlap and curvature effects [(D-R/lambda) x (D-R/D-P)]. Based on this, we devised a phenomenological model as an extension to the existing flat surface theory, which can successfully predict the average surface charge around a rough/patterned nanoparticle as a function of the particle size, roughness size, and pH. |
Toprak, K; Ouedraogo, K E Effect of storage tanks on solar-powered absorption chiller cooling system performance Journal Article International Journal of Energy Research, 44 (6), pp. 4366-4375, 2020. @article{Toprak20204366, title = {Effect of storage tanks on solar-powered absorption chiller cooling system performance}, author = {K Toprak and K E Ouedraogo}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85079718680&doi=10.1002%2fer.5210&partnerID=40&md5=aa6c4b8eb29c64ec8849ffdd43934cc6}, doi = {10.1002/er.5210}, year = {2020}, date = {2020-01-01}, journal = {International Journal of Energy Research}, volume = {44}, number = {6}, pages = {4366-4375}, abstract = {Thermal storage, low power tariff at night, and low nocturnal temperature can be used in synergy to reduce the cooling costs of the solar-powered absorption chiller cooling systems. This study aims to reduce the required cooling capacity of an absorption chiller (ACH) powered by a solar parabolic trough collector (PTC) and a backup fuel boiler by integrating thermal storage tanks. The thermal performance of the system is simulated for a building that is cooled for 14 h/day. The system uses 1000 m2 PTC with 1020 kW ACH. Chilled water storage (CHWS) and cooling water storage (CWS) effects on the system performance for different operation hours per day of the ACH under Izmir (Turkey) and Phoenix (USA) weather conditions are analyzed. When the ACH operates 14 h/day as the load for both systems and both locations, the variations of the solar collector efficiency and the cooling load to heat input ratio remain less than 4% after the modifications. From the addition of CHWS to the reference system, a parametric study consisting of changing the ACH operation hours per day shows that the required cooling capacity of the ACH can be reduced to 34%. The capacity factor of the ACH is improved from its reference value of 41% up to 96%. © 2020 John Wiley & Sons Ltd}, keywords = {}, pubstate = {published}, tppubtype = {article} } Thermal storage, low power tariff at night, and low nocturnal temperature can be used in synergy to reduce the cooling costs of the solar-powered absorption chiller cooling systems. This study aims to reduce the required cooling capacity of an absorption chiller (ACH) powered by a solar parabolic trough collector (PTC) and a backup fuel boiler by integrating thermal storage tanks. The thermal performance of the system is simulated for a building that is cooled for 14 h/day. The system uses 1000 m2 PTC with 1020 kW ACH. Chilled water storage (CHWS) and cooling water storage (CWS) effects on the system performance for different operation hours per day of the ACH under Izmir (Turkey) and Phoenix (USA) weather conditions are analyzed. When the ACH operates 14 h/day as the load for both systems and both locations, the variations of the solar collector efficiency and the cooling load to heat input ratio remain less than 4% after the modifications. From the addition of CHWS to the reference system, a parametric study consisting of changing the ACH operation hours per day shows that the required cooling capacity of the ACH can be reduced to 34%. The capacity factor of the ACH is improved from its reference value of 41% up to 96%. © 2020 John Wiley & Sons Ltd |
Ozcelik, H G; Sozen, Y; Sahin, H; Barisik, M Parametrizing nonbonded interactions between silica and water from first principles Journal Article Applied Surface Science, 504 , 2020, (cited By 2). @article{Ozcelik2020, title = {Parametrizing nonbonded interactions between silica and water from first principles}, author = {H G Ozcelik and Y Sozen and H Sahin and M Barisik}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85075459998&doi=10.1016%2fj.apsusc.2019.144359&partnerID=40&md5=edc43d7aa69a9dad5f9eca3aca86e4fa}, doi = {10.1016/j.apsusc.2019.144359}, year = {2020}, date = {2020-01-01}, journal = {Applied Surface Science}, volume = {504}, note = {cited By 2}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Ozcelik, H G; Ozdemir, A C; Kim, B; Barisik, M Wetting of single crystalline and amorphous silicon surfaces: effective range of intermolecular forces for wetting Journal Article Molecular Simulation, 46 (3), pp. 224-234, 2020, (cited By 3). @article{Ozcelik2020224, title = {Wetting of single crystalline and amorphous silicon surfaces: effective range of intermolecular forces for wetting}, author = {H G Ozcelik and A C Ozdemir and B Kim and M Barisik}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85075451686&doi=10.1080%2f08927022.2019.1690145&partnerID=40&md5=de3ea34b7359d5d74fbc29c3cd7ee7f6}, doi = {10.1080/08927022.2019.1690145}, year = {2020}, date = {2020-01-01}, journal = {Molecular Simulation}, volume = {46}, number = {3}, pages = {224-234}, note = {cited By 3}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2019 |
Acarer, Sercan; Özkol, Ünver Off-Design Analysis of Transonic Bypass Fan Systems Using Streamline Curvature Through-Flow Method Journal Article International Journal of Turbo and Jet Engines, 36 (2), pp. 137 – 146, 2019, (All Open Access, Green Open Access). @article{Acarer2019137, title = {Off-Design Analysis of Transonic Bypass Fan Systems Using Streamline Curvature Through-Flow Method}, author = {Sercan Acarer and Ünver Özkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85046815136&doi=10.1515%2ftjj-2016-0083&partnerID=40&md5=3b24de44dd45ff48c0814f96a18258cc}, doi = {10.1515/tjj-2016-0083}, year = {2019}, date = {2019-01-01}, journal = {International Journal of Turbo and Jet Engines}, volume = {36}, number = {2}, pages = {137 – 146}, abstract = {The two-dimensional streamline curvature through-flow modeling of turbomachinery is still a key element for turbomachinery preliminary analysis. Basically, axisymmetric swirling flow field is solved numerically. The effects of blades are imposed as sources of swirl, work input/output and entropy generation. Although the topic is studied vastly in the literature for compressors and turbines, combined modeling of the transonic fan and the downstream splitter of turbofan engine configuration, to the authors' best knowledge, is limited. In a prior study, the authors presented a new method for bypass fan modeling for inverse design calculations. Moreover, new set of practical empirical correlations are calibrated and validated. This paper is an extension of this study to rapid off-design analysis of transonic by-pass fan systems. The methodology is validated by two test cases: NASA 2-stage fan and GE-NASA bypass fan case. The proposed methodology is a simple extension for streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effort. © 2019 Walter de Gruyter GmbH, Berlin/Boston.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } The two-dimensional streamline curvature through-flow modeling of turbomachinery is still a key element for turbomachinery preliminary analysis. Basically, axisymmetric swirling flow field is solved numerically. The effects of blades are imposed as sources of swirl, work input/output and entropy generation. Although the topic is studied vastly in the literature for compressors and turbines, combined modeling of the transonic fan and the downstream splitter of turbofan engine configuration, to the authors' best knowledge, is limited. In a prior study, the authors presented a new method for bypass fan modeling for inverse design calculations. Moreover, new set of practical empirical correlations are calibrated and validated. This paper is an extension of this study to rapid off-design analysis of transonic by-pass fan systems. The methodology is validated by two test cases: NASA 2-stage fan and GE-NASA bypass fan case. The proposed methodology is a simple extension for streamline curvature method and can be applied to existing compressor methodologies with minimum numerical effort. © 2019 Walter de Gruyter GmbH, Berlin/Boston. |
Celik, Hasan; Mobedi, Moghtada; Nakayama, Akira; Ozkol, Unver Journal of Porous Media, 22 (5), pp. 511 – 529, 2019, (All Open Access, Green Open Access). @article{Celik2019511, title = {A study on numerical determination of permeability and inertia coefficient of aluminum foam using X-ray microtomography technique: Focus on inspection methods for reliability (permeability and inertia coefficient by tomography)}, author = {Hasan Celik and Moghtada Mobedi and Akira Nakayama and Unver Ozkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85065613946&doi=10.1615%2fJPorMedia.2019028887&partnerID=40&md5=cc89991bf14176783bc2c187db3358c8}, doi = {10.1615/JPorMedia.2019028887}, year = {2019}, date = {2019-01-01}, journal = {Journal of Porous Media}, volume = {22}, number = {5}, pages = {511 – 529}, abstract = {The volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%. © 2019 by Begell House, Inc.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } The volume-averaged (i.e., macroscopic) transport properties such as permeability and inertia coefficient of two aluminum foams with 10 and 20 pores per inch (PPI) pore density are found using microtomography images. It is shown that a comparison between the numerical values and the experimental results may not be sufficient to prove the correctness of the obtained results. Hence, in addition to traditional validation methods such as grid independency and comparison with reported results in literature, further inspections such as (a) checking the development of flow, (b) inspection of Darcy and non-Darcy regions, (c) conservation of flow rate through the porous media, (d) sufficiency of number of voxels in the narrow throats, and (e) observation of transverse velocity gradients in pores for high and low Reynolds numbers can be performed to further validate the achieved results. These techniques have been discussed and explained in detail for the performed study. Moreover, the obtained permeability and inertia coefficient values are compared with 19 reported theoretical, numerical, and experimental studies. The maximum deviation between the present results and the reported studies for 10 PPI is below 25%, while for 20 PPI it is below 28%. © 2019 by Begell House, Inc. |
2018 |
Kor, Orcun; Acarer, Sercan; Ozkol, Unver Aerodynamic optimization of through-flow design model of a high by-pass transonic aero-engine fan using genetic algorithm Journal Article PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, 232 (3), pp. 211-224, 2018, ISSN: 0957-6509. @article{ISI:000435491500001, title = {Aerodynamic optimization of through-flow design model of a high by-pass transonic aero-engine fan using genetic algorithm}, author = {Orcun Kor and Sercan Acarer and Unver Ozkol}, doi = {10.1177/0957650917730466}, issn = {0957-6509}, year = {2018}, date = {2018-05-01}, journal = {PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY}, volume = {232}, number = {3}, pages = {211-224}, abstract = {This study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors' best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbo-machinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This study deals with aerodynamic optimization of a high by-pass transonic aero-engine fan module in a through-flow inverse design model at cruise condition. To the authors' best knowledge, although the literature contains through-flow optimization of the simplified cases of compressors and turbines, an optimization study targeting the more elaborate case of combined transonic fan and splitter through-flow model is not considered in the literature. Such a through-flow optimization of a transonic fan, combined with bypass and core streams separated by an aerodynamically shaped flow splitter, possesses significant challenges to any optimizer, due to highly non-linear nature of the problem and the high number of constraints, including the fulfillment of the targeted bypass ratio. It is the aim of this study to consider this previously untouched area in detail and therefore present a more sophisticated and accurate optimization environment for actual bypass fan systems. An in-house optimization code using genetic algorithm is coupled with a previously developed in-house through-flow solver which is using a streamline curvature technique and a set of in-house calibrated empirical models for incidence, deviation, loss and blockage. As the through-flow models are the backbone of turbo-machinery design, and great majority of design decisions are taken in this phase, such a study is assessed to result in significant guidelines to the gas turbine community. |
Celik, Hasan; Mobedi, Moghtada; Nakayama, Akira; Ozkol, Unver Numerical Heat Transfer; Part A: Applications, 74 (7), pp. 1368 – 1386, 2018, (All Open Access, Green Open Access). @article{Celik20181368, title = {A numerical study on determination of volume averaged thermal transport properties of metal foam structures using X-ray microtomography technique}, author = {Hasan Celik and Moghtada Mobedi and Akira Nakayama and Unver Ozkol}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85057255888&doi=10.1080%2f10407782.2018.1494936&partnerID=40&md5=48bd8293534537dec7583acb2bf5c66f}, doi = {10.1080/10407782.2018.1494936}, year = {2018}, date = {2018-01-01}, journal = {Numerical Heat Transfer; Part A: Applications}, volume = {74}, number = {7}, pages = {1368 – 1386}, abstract = {Volume averaged thermal transport properties of two metal foams with 10 and 20 PPI are obtained by using microtomography technique. The digital 3D structures of samples are generated in computer environment. The governing equations are solved for the entire domain and the volume averaged technique is used to determine interfacial heat transfer coefficient, longitudinal and transverse thermal dispersion conductivity. The study is performed for the pore scale Reynolds number from 100 to 600. The obtained results are within the ranges of the suggested correlations in literature. The present study supports the correlations suggested by Calmidi and Mahajan (2000) and Zhang et al. (2016). © 2018, © 2018 Taylor & Francis Group, LLC.}, note = {All Open Access, Green Open Access}, keywords = {}, pubstate = {published}, tppubtype = {article} } Volume averaged thermal transport properties of two metal foams with 10 and 20 PPI are obtained by using microtomography technique. The digital 3D structures of samples are generated in computer environment. The governing equations are solved for the entire domain and the volume averaged technique is used to determine interfacial heat transfer coefficient, longitudinal and transverse thermal dispersion conductivity. The study is performed for the pore scale Reynolds number from 100 to 600. The obtained results are within the ranges of the suggested correlations in literature. The present study supports the correlations suggested by Calmidi and Mahajan (2000) and Zhang et al. (2016). © 2018, © 2018 Taylor & Francis Group, LLC. |
2017 |
Cetin, Eylem; Cetkin, Erdal The effect of cavities and T-shaped assembly of fins on overall thermal resistances Journal Article INTERNATIONAL JOURNAL OF HEAT AND TECHNOLOGY, 35 (4), pp. 944-952, 2017, ISSN: 0392-8764. @article{ISI:000429132900030, title = {The effect of cavities and T-shaped assembly of fins on overall thermal resistances}, author = {Eylem Cetin and Erdal Cetkin}, doi = {10.18280/ijht.350430}, issn = {0392-8764}, year = {2017}, date = {2017-12-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND TECHNOLOGY}, volume = {35}, number = {4}, pages = {944-952}, abstract = {In this study, authors show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effect of the cavities and the fins on overall thermal resistances were compared while their volume fraction in a unit volume element is fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of design on the flow characteristics and the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries correspond to the lower peak temperature. In addition, the results also show that there is an optimal cavity shape that minimizes the peak temperature. This optimal shape becomes thinner when the number of the cavities increase. In parallel flow case, fins with thicker and shorter stem and longer tributaries correspond to the minimum excess temperature. In addition, the longer and thinner cavities increase the thermal performance in parallel flow case.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this study, authors show that maximum excess temperature on a heat generating cylindrical solid domain can be minimized with numerically optimized rectangular cavities and T-shaped fins. The effect of the cavities and the fins on overall thermal resistances were compared while their volume fraction in a unit volume element is fixed. Furthermore, the designs correspond to the minimum thermal resistance were uncovered for two types of flows; parallel and cross-flow. The governing equations of the heat transfer and the fluid flow were solved simultaneously in order to show the effects of design on the flow characteristics and the thermal performance. Two-dimensional solution domain was used to uncover the thermal performance in cross-flow case because the flow direction is perpendicular to the heat transfer surface area of the heat generating domain. However, three-dimensional domain was used in parallel flow case because the fluid flows along the outer surface of the heat generating domain. For the cross-flow case, the results show that T-shaped assembly of fins with longer stem and shorter tributaries correspond to the lower peak temperature. In addition, the results also show that there is an optimal cavity shape that minimizes the peak temperature. This optimal shape becomes thinner when the number of the cavities increase. In parallel flow case, fins with thicker and shorter stem and longer tributaries correspond to the minimum excess temperature. In addition, the longer and thinner cavities increase the thermal performance in parallel flow case. |
Celebi, Alper Tunga; Barisik, Murat; Beskok, Ali Electric field controlled transport of water in graphene nano-channels Journal Article JOURNAL OF CHEMICAL PHYSICS, 147 (16), 2017, ISSN: 0021-9606. @article{ISI:000414177600067, title = {Electric field controlled transport of water in graphene nano-channels}, author = {Alper Tunga Celebi and Murat Barisik and Ali Beskok}, doi = {10.1063/1.4996210}, issn = {0021-9606}, year = {2017}, date = {2017-10-01}, journal = {JOURNAL OF CHEMICAL PHYSICS}, volume = {147}, number = {16}, abstract = {Motivated by electrowetting-based flow control in nano-systems, water transport in graphene nano-channels is investigated as a function of the applied electric field. Molecular dynamics simulations are performed for deionized water confined in graphene nano-channels subjected to opposing surface charges, creating an electric field across the channel. Water molecules respond to the electric field by reorientation of their dipoles. Oxygen and hydrogen atoms in water face the anode and cathode, respectively, and hydrogen atoms get closer to the cathode compared to the oxygen atoms near the anode. These effects create asymmetric density distributions that increase with the applied electric field. Force-driven water flows under electric fields exhibit asymmetric velocity profiles and unequal slip lengths. Apparent viscosity of water increases and the slip length decreases with increased electric field, reducing the flow rate. Increasing the electric field above a threshold value freezes water at room temperature. Published by AIP Publishing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Motivated by electrowetting-based flow control in nano-systems, water transport in graphene nano-channels is investigated as a function of the applied electric field. Molecular dynamics simulations are performed for deionized water confined in graphene nano-channels subjected to opposing surface charges, creating an electric field across the channel. Water molecules respond to the electric field by reorientation of their dipoles. Oxygen and hydrogen atoms in water face the anode and cathode, respectively, and hydrogen atoms get closer to the cathode compared to the oxygen atoms near the anode. These effects create asymmetric density distributions that increase with the applied electric field. Force-driven water flows under electric fields exhibit asymmetric velocity profiles and unequal slip lengths. Apparent viscosity of water increases and the slip length decreases with increased electric field, reducing the flow rate. Increasing the electric field above a threshold value freezes water at room temperature. Published by AIP Publishing. |
Kalyoncu, Gulce; Barisik, Murat Analytical solution of micro-/nanoscale convective liquid flows in tubes and slits Journal Article MICROFLUIDICS AND NANOFLUIDICS, 21 (9), 2017, ISSN: 1613-4982. @article{ISI:000410286400004, title = {Analytical solution of micro-/nanoscale convective liquid flows in tubes and slits}, author = {Gulce Kalyoncu and Murat Barisik}, doi = {10.1007/s10404-017-1985-5}, issn = {1613-4982}, year = {2017}, date = {2017-09-01}, journal = {MICROFLUIDICS AND NANOFLUIDICS}, volume = {21}, number = {9}, abstract = {Analytical solutions examining heat transport in micro-/nanoscale liquid flows were developed. Using the energy equation coupled with fully developed velocity, we solved developing temperature profiles with axial conduction and viscous dissipation terms. A comprehensive literature review provided the published range of velocity slip and temperature jump conditions. While molecular simulations and experiments present constant slip and jump values for a specific liquid/surface couple independent of confinement size, non-dimensional forms of these boundary conditions were found appropriate to calculate non-equilibrium as a function of flow height. Although slip and jump conditions are specific for each liquid/surface couple and hard to obtain, we proposed modeling of the slip and jump as a function of the surface wetting, in order to create a general, easy to measure methodology. We further developed possible correlations to calculate jump using the slip value of the corresponding surface and tested in the results. Fully developed Nu showed strong dependence on slip and jump. Heat transfer stopped when slip and jump coefficients became higher than a certain value. Strong variation of Nu in the thermal development length was observed for low slip and jump cases, while an almost constant Nu in the flow direction was found for high slip and jump coefficients. Variation of temperature profiles was found to dominate the heat transfer through the constant temperature surface while surface and liquid temperatures became equal at heat transfer lengths comparable with confinement sizes for no-dissipation cases. In case of non-negligible heat dissipation, viscous heating dominated the Nu value by enhancing the heating while decreasing the heat removal in cooling cases. Implementation of proposed procedure on a micro-channel convection problem from a micro-fluidics application showed the dominant effect of the model defining the slip and jump relationship. Direct use of kinetic gas theory resulted in an increase of Nu by an increase in non-equilibrium, while models developed from published liquid slip and jump values produced an opposite behavior.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Analytical solutions examining heat transport in micro-/nanoscale liquid flows were developed. Using the energy equation coupled with fully developed velocity, we solved developing temperature profiles with axial conduction and viscous dissipation terms. A comprehensive literature review provided the published range of velocity slip and temperature jump conditions. While molecular simulations and experiments present constant slip and jump values for a specific liquid/surface couple independent of confinement size, non-dimensional forms of these boundary conditions were found appropriate to calculate non-equilibrium as a function of flow height. Although slip and jump conditions are specific for each liquid/surface couple and hard to obtain, we proposed modeling of the slip and jump as a function of the surface wetting, in order to create a general, easy to measure methodology. We further developed possible correlations to calculate jump using the slip value of the corresponding surface and tested in the results. Fully developed Nu showed strong dependence on slip and jump. Heat transfer stopped when slip and jump coefficients became higher than a certain value. Strong variation of Nu in the thermal development length was observed for low slip and jump cases, while an almost constant Nu in the flow direction was found for high slip and jump coefficients. Variation of temperature profiles was found to dominate the heat transfer through the constant temperature surface while surface and liquid temperatures became equal at heat transfer lengths comparable with confinement sizes for no-dissipation cases. In case of non-negligible heat dissipation, viscous heating dominated the Nu value by enhancing the heating while decreasing the heat removal in cooling cases. Implementation of proposed procedure on a micro-channel convection problem from a micro-fluidics application showed the dominant effect of the model defining the slip and jump relationship. Direct use of kinetic gas theory resulted in an increase of Nu by an increase in non-equilibrium, while models developed from published liquid slip and jump values produced an opposite behavior. |
Cetkin, Erdal JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME, 139 (8), 2017, ISSN: 0022-1481. @article{ISI:000426124400018, title = {Constructal Microdevice Manifold Design With Uniform Flow Rate Distribution by Consideration of the Tree-Branching Rule of Leonardo da Vinci and Hess-Murray Rule}, author = {Erdal Cetkin}, doi = {10.1115/1.4036089}, issn = {0022-1481}, year = {2017}, date = {2017-08-01}, journal = {JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME}, volume = {139}, number = {8}, abstract = {In this paper, we show how the design of a microdevice manifold should be tapered for uniform flow rate distribution. The designs based on the tree-branching rule of Leonardo da Vinci and the Hess-Murray rule were considered in addition to the constructal design. Both da Vinci and Hess-Murray designs are insensitive to the inlet velocity, and they provide better flow uniformity than the base (not tapered) design. However, the results of this paper uncover that not only pressure drop but also velocity distribution in the microdevice play an integral role in the flow uniformity. Therefore, an iterative approach was adopted with five degrees-of-freedom (inclined wall positions) and one constraint (constant distribution channel thickness) in order to uncover the constructal design which conforms the uniform flow rate distribution. In addition, the effect of slenderness of the microchannels (Svelteness) and inlet velocity on the flow rate distribution to the microchannels has been documented. This paper also uncovers that the design of a manifold should be designed with not only the consideration of pressure distribution but also dynamic pressure distribution especially for non-Svelte microdevices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we show how the design of a microdevice manifold should be tapered for uniform flow rate distribution. The designs based on the tree-branching rule of Leonardo da Vinci and the Hess-Murray rule were considered in addition to the constructal design. Both da Vinci and Hess-Murray designs are insensitive to the inlet velocity, and they provide better flow uniformity than the base (not tapered) design. However, the results of this paper uncover that not only pressure drop but also velocity distribution in the microdevice play an integral role in the flow uniformity. Therefore, an iterative approach was adopted with five degrees-of-freedom (inclined wall positions) and one constraint (constant distribution channel thickness) in order to uncover the constructal design which conforms the uniform flow rate distribution. In addition, the effect of slenderness of the microchannels (Svelteness) and inlet velocity on the flow rate distribution to the microchannels has been documented. This paper also uncovers that the design of a manifold should be designed with not only the consideration of pressure distribution but also dynamic pressure distribution especially for non-Svelte microdevices. |
Cetkin, E VASCULAR STRUCTURES FOR SMART FEATURES: SELF-COOLING AND SELF-HEALING Journal Article JOURNAL OF THERMAL ENGINEERING, 3 (4, 5), pp. 1338-1345, 2017, ISSN: 2148-7847. @article{ISI:000407804200004, title = {VASCULAR STRUCTURES FOR SMART FEATURES: SELF-COOLING AND SELF-HEALING}, author = {E Cetkin}, doi = {10.18186/journal-of-thermal-engineering.330185}, issn = {2148-7847}, year = {2017}, date = {2017-08-01}, journal = {JOURNAL OF THERMAL ENGINEERING}, volume = {3}, number = {4, 5}, pages = {1338-1345}, abstract = {Here we show how smart features of self-cooling and self-healing can be gained to mechanical systems with embedded vascular structures. Vascular structures mimic the circulatory system of animals. Similar to blood distribution from heart to the animal body, vascular channels provide the distribution of coolant and/or healing agent from a point to the entire body of a mechanic system. Thus the mechanic system becomes capable of cooling itself under unpredictable heat attacks and capable of healing itself as cracks occur due to applied mechanical loads. These smart features are necessary for advanced devices, equipment and vehicles. The essential design parameter is vascularization in order to provide smart features. There are distinct configurations for vascularization such as radial, tree-shaped, grid and hybrids of these designs. In addition, several theories are available for the shape optimization of vascular structures such as fractal theory and constructal theory. Unlike fractal theory, constructal theory does not include constraints based on generic algorithms and dictated assumptions. Therefore, constructal theory approach is discussed in this paper. This paper shows how smart features can be gained to a mechanical system while its weight decreases and its mechanical strength increases simultaneously.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Here we show how smart features of self-cooling and self-healing can be gained to mechanical systems with embedded vascular structures. Vascular structures mimic the circulatory system of animals. Similar to blood distribution from heart to the animal body, vascular channels provide the distribution of coolant and/or healing agent from a point to the entire body of a mechanic system. Thus the mechanic system becomes capable of cooling itself under unpredictable heat attacks and capable of healing itself as cracks occur due to applied mechanical loads. These smart features are necessary for advanced devices, equipment and vehicles. The essential design parameter is vascularization in order to provide smart features. There are distinct configurations for vascularization such as radial, tree-shaped, grid and hybrids of these designs. In addition, several theories are available for the shape optimization of vascular structures such as fractal theory and constructal theory. Unlike fractal theory, constructal theory does not include constraints based on generic algorithms and dictated assumptions. Therefore, constructal theory approach is discussed in this paper. This paper shows how smart features can be gained to a mechanical system while its weight decreases and its mechanical strength increases simultaneously. |
Celik, Hasan; Mobedi, Moghtada; Manca, Oronzio; Ozkol, Unver A pore scale analysis for determination of interfacial convective heat transfer coefficient for thin periodic porousmedia undermixed convection Journal Article INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW, 27 (12), pp. 2775-2798, 2017, ISSN: 0961-5539. @article{ISI:000416431600006b, title = {A pore scale analysis for determination of interfacial convective heat transfer coefficient for thin periodic porousmedia undermixed convection}, author = {Hasan Celik and Moghtada Mobedi and Oronzio Manca and Unver Ozkol}, doi = {10.1108/HFF-01-2017-0036}, issn = {0961-5539}, year = {2017}, date = {2017-01-01}, journal = {INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW}, volume = {27}, number = {12}, pages = {2775-2798}, abstract = {Purpose - The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under mixed convection heat transfer. Design/methodology/approach - The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous media, numerically. The velocity and temperature fields for different values of porosity, Ri and Re numbers are obtained. The study is performed for the range of Ri number from 0.01 to 10, Re number from 100 to 500 and porosity value from 0.51 to 0.96. Based on the obtained results, the value of the interfacial convective heat transfer coefficient is calculated by using volume average method. Findings - It was found that at low porosities (such as 0.51), the interfacial Nusselt number does not considerably change with Ri and Re numbers. However, for porous media with high Ri number and porosity (such as 10 and 0.51, respectively), secondary flows occur in the middle of the channel between rods improving heat transfer between solid and fluid, considerably. It is shown that the available correlations of interfacial heat transfer coefficient suggested for forced convection can be used for mixed convection for the porous media with low porosity (such as 0.51) or for the flow with low Ri number (such as 0.01). Originality/value - To the best of the authors' knowledge, there is no study on determination of interfacial convective heat transfer coefficient for mixed convection in porous media in literature. The present study might be the first study providing an accurate idea on the range of this important parameter, which will be useful particularly for researchers who study on mixed convection heat transfer in porous media, macroscopically.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Purpose - The purpose of this study is to determine interfacial convective heat transfer coefficient numerically, for a porous media consisting of square blocks in inline arrangement under mixed convection heat transfer. Design/methodology/approach - The continuity, momentum and energy equations are solved in dimensionless form for a representative elementary volume of porous media, numerically. The velocity and temperature fields for different values of porosity, Ri and Re numbers are obtained. The study is performed for the range of Ri number from 0.01 to 10, Re number from 100 to 500 and porosity value from 0.51 to 0.96. Based on the obtained results, the value of the interfacial convective heat transfer coefficient is calculated by using volume average method. Findings - It was found that at low porosities (such as 0.51), the interfacial Nusselt number does not considerably change with Ri and Re numbers. However, for porous media with high Ri number and porosity (such as 10 and 0.51, respectively), secondary flows occur in the middle of the channel between rods improving heat transfer between solid and fluid, considerably. It is shown that the available correlations of interfacial heat transfer coefficient suggested for forced convection can be used for mixed convection for the porous media with low porosity (such as 0.51) or for the flow with low Ri number (such as 0.01). Originality/value - To the best of the authors' knowledge, there is no study on determination of interfacial convective heat transfer coefficient for mixed convection in porous media in literature. The present study might be the first study providing an accurate idea on the range of this important parameter, which will be useful particularly for researchers who study on mixed convection heat transfer in porous media, macroscopically. |
2016 |
Kalyoncu, Gulce; Barisik, Murat The extended Graetz problem for micro-slit geometries; analytical coupling of rarefaction, axial conduction and viscous dissipation Journal Article INTERNATIONAL JOURNAL OF THERMAL SCIENCES, 110 , pp. 261-269, 2016, ISSN: 1290-0729. @article{ISI:000382793600021, title = {The extended Graetz problem for micro-slit geometries; analytical coupling of rarefaction, axial conduction and viscous dissipation}, author = {Gulce Kalyoncu and Murat Barisik}, doi = {10.1016/j.ijthermalsci.2016.07.009}, issn = {1290-0729}, year = {2016}, date = {2016-12-01}, journal = {INTERNATIONAL JOURNAL OF THERMAL SCIENCES}, volume = {110}, pages = {261-269}, abstract = {In order to support the recent MEMS and Lab-on-a-chip technologies, we studied heat transport in micro-scale slit channel gas flows. Since the micro convection transport phenomena diverges from conventional macro-scale transport due to rarefaction, axial conduction and viscous heating, an accurate understanding requires a complete coupling of these effects. For such cases, we studied heat transfer in hydrodynamically developed, thermally developing gas flows in micro-slits at various flow conditions. The analytical solution of the energy equation considered both the heat conduction in the axial direction and heat dissipation of viscous forces. Furthermore, updated boundary conditions of velocity slip and temperature jump were applied based on Knudsen number of flow in order to account for the non equilibrium gas dynamics. Local Nusselt number (Nu) values were calculated as a function of Peclet (Pe), Knudsen (Kn) and Brinkman (Br) numbers which were selected carefully according to possible micro-flow cases. Strong variation of Nu in thermal development length was found to dominate heat transfer behavior of micro-slits with short heating lengths for early slip flow regime. For this instance, influence of axial conduction and viscous dissipation was equally important. On the other hand, high Kn slip flow suppressed the axial conduction while viscous heating in a small surface-gas temperature difference case mostly determined the fully developed Nu and average heat transfer behavior as a function of Kn value. (C) 2016 Elsevier Masson SAS. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In order to support the recent MEMS and Lab-on-a-chip technologies, we studied heat transport in micro-scale slit channel gas flows. Since the micro convection transport phenomena diverges from conventional macro-scale transport due to rarefaction, axial conduction and viscous heating, an accurate understanding requires a complete coupling of these effects. For such cases, we studied heat transfer in hydrodynamically developed, thermally developing gas flows in micro-slits at various flow conditions. The analytical solution of the energy equation considered both the heat conduction in the axial direction and heat dissipation of viscous forces. Furthermore, updated boundary conditions of velocity slip and temperature jump were applied based on Knudsen number of flow in order to account for the non equilibrium gas dynamics. Local Nusselt number (Nu) values were calculated as a function of Peclet (Pe), Knudsen (Kn) and Brinkman (Br) numbers which were selected carefully according to possible micro-flow cases. Strong variation of Nu in thermal development length was found to dominate heat transfer behavior of micro-slits with short heating lengths for early slip flow regime. For this instance, influence of axial conduction and viscous dissipation was equally important. On the other hand, high Kn slip flow suppressed the axial conduction while viscous heating in a small surface-gas temperature difference case mostly determined the fully developed Nu and average heat transfer behavior as a function of Kn value. (C) 2016 Elsevier Masson SAS. All rights reserved. |
Yenigun, O; Cetkin, E Experimental and numerical investigation of constructal vascular channels for self-cooling: Parallel channels, tree-shaped and hybrid designs Journal Article INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 103 , pp. 1155-1165, 2016, ISSN: 0017-9310. @article{ISI:000384777800107b, title = {Experimental and numerical investigation of constructal vascular channels for self-cooling: Parallel channels, tree-shaped and hybrid designs}, author = {O Yenigun and E Cetkin}, doi = {10.1016/j.ijheatmasstransfer.2016.08.074}, issn = {0017-9310}, year = {2016}, date = {2016-12-01}, journal = {INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, volume = {103}, pages = {1155-1165}, abstract = {In this paper, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: parallel channels, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from parallel channels to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain, which increases the conductive resistances. Therefore, additional channels were inserted at the uncooled regions in the tree-shaped design (hybrid design). The best features of both parallel channels and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and parallel channels designs, respectively. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows. (C) 2016 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this paper, we show experimentally and numerically how a plate which is subjected to a constant heat load can be kept under an allowable temperature limit. Vascular channels in which coolant fluid flows have been embedded in the plate. Three types of vascular channel designs were compared: parallel channels, tree-shaped and their hybrid. The effects of channel design on the thermal performance for different volume fractions (the fluid volume over the solid volume) are documented. In addition, the effects of the number of channels on cooling performance have been documented. Changing the design from parallel channels to tree-shaped designs decreases the order of pressure drop. Hence increase in the order of the convective heat transfer coefficient is achieved. However, tree-shaped designs do not bathe the entire domain, which increases the conductive resistances. Therefore, additional channels were inserted at the uncooled regions in the tree-shaped design (hybrid design). The best features of both parallel channels and tree-shaped designs are combined in the hybrid of them: the flow resistances to the fluid and heat flow become almost as low as the tree-shaped and parallel channels designs, respectively. The effect of design on the maximum temperature shows that there should be an optimum design for a distinct set of boundary conditions, and this design should be varied as the boundary conditions change. This result is in accord with the constructal law, i.e. the shape should be varied in order to minimize resistances to the flows. (C) 2016 Elsevier Ltd. All rights reserved. |
Project Title | Director of the Project | Start Date | Funds |
| Jeotermal enerji araştırma-geliştirme, test ve eğitim Merkezi | Prof. Dr. Zafer İLKEN | 2002 | DPT |
| Biyoteknoloji ve Biyomühendislik Araştırma Merkezi | Prof. Dr. Barış ÖZERDEM (Proje Eş Yürütücü) | 2007 | DPT |
| Adsorpsiyonlu Isı Pompası | Doç. Dr. M. Mobedi | 2006 | DPT |
| Evaluation Of Geothermal Developments In Turkey From The Clean Energy Point Of View. Case Studies: Balcova District Heating System-Izmir And Kizildere Geothermal Power Plant-Denizli | Prof. Dr. Gülden Gökçen | 2005 | TÜBİTAK |
| Jet Akışlarındaki Kararsızlıkların Kontrolü İle Isı Transferinin Arttırılması | Yrd.Doç.Dr. Ünver Özkol | 2008 | TÜBİTAK |
| İYTE Kampüs Alanındaki Rüzgar Enerjisi Potansiyelinin Ölçülmesi | Prof. Dr. Barış ÖZERDEM | 2000 | İYTE-BAP |
| Alüminyum Köpük Malzeme ile İmal Edilmiş Hava Tipi Güneş Kollektörlerinin Analizi | Prof.Dr. Zafer İLKEN | 2001 | İYTE-BAP |
| Jeotermal Enerjide Kullanılan Kuyu İçi Eşanjör Performanslarının Artırılması | Prof.Dr. Zafer İLKEN | 2001 | İYTE-BAP |
| Endüstriyel Ürün Tasarımının , Üretiminin ve Mühendisliğinin ( CAD/CAM/CAE) Profesyonel Amaçlı Bir Hizmet Sektörü Olarak İnternet Ortamında Gerçekleştirilmesine Yönelik İnteraktif Bir Stüdyo Modeli : E- Stüdyo | Prof. Dr. Barış ÖZERDEM (Ortak Yürütücü) | 2000 | İYTE-BAP |
| Rüzgar Türbinlerinde Verim Arttırmaya ve Veri Toplamaya Yönelik Bir Bilgisayar Kontrol Sistemi Geliştirilmesi | Prof. Dr. Barış ÖZERDEM | 2005 | İYTE-BAP |
| Sinüsoidal ve “Offset Strip” tipindeki ısı değiştirici kanallarda akışın görüntülenmesi ve CDF ile karşılaştırılması | Yrd.Doç.Dr. Ünver Özkol | 2008 | İYTE-BAP |
| Kamu Binalarında Enerji Verimliliği: İyte İdari Bina’nın Enerji Performansının Belirlenmesi | Prof. Dr. Gülden Gökçen | 2005 | İYTE-BAP |
| Tarımsal Ürünlerin Kurutulmasında Kurutma Parametrelerinin Belirlenmesi | Prof. Dr. Gülden Gökçen | 2006 | İYTE-BAP |
| Moleküler Seviyede Nano-Ölçek Gaz Akışlarının İncelenmesi | Yrd. Doç. Dr. Murat Barışık | 2015 | Marie Skłodowska-Curie COFUND |
| Adsorpsiyon Yatak Isı Pompası Kullanılarak Buzdolabı Verimliliğinin Artırılması | Yrd. Doç. Dr. Murat Barışık | 2015 | SANTEZ Projesi |
| Momentum Flux, Phase Doppler Anemonetry and High Speed Imaging Analysis of GDI injector under flash boiling conditions | Yrd. Doç. Dr. Alvero Diez Rodriguez | 2014 | TÜBİTAK |
| Biodiesel Spray Investigation in a Constant Volume Combustion Chamber | Yrd. Doç. Dr. Alvero Diez Rodriguez | 2013 | TÜBİTAK |
| Türkiye’nin Farklı İklim Koşullarında Isıl Konfor Sıcaklıklarına Bağlı Olarak Konutların Enerji Performanslarının Değerlendirilmesi | Prof. Dr. Gülden Gökçen | 2012 | TTMD |
| Konutlarda Enerji Performansı Standard Değerlendirme Metodu (KEP-SDM) | Prof. Dr. Gülden Gökçen | 2010 | TMMOB |
