A parametric analysis has been conducted for the phase change material (PCM)-air cooled battery p... more A parametric analysis has been conducted for the phase change material (PCM)-air cooled battery pack. The system is composed of 26650 lithium-ion LiFePO4 batteries enclosed by PCM. A one-dimensional thermal model for the PCM domain is developed using the enthalpy method. The finite volume method is employed to solve the energy equation for both cell and PCM domain. The developed computational algorithm has been validated as a result of the simulations for the same conditions with the literature. The discharge process of the batteries has been investigated for 2C, 3C, and 5C rates. Thermal analyses have been performed for passive (natural convection) and active cooling (forced convection). It is aimed to keep the temperature of the battery cell under critical levels. A parametric investigation for crucial parameters like PCM layer thickness, the thermal conductivity of the PCM, arrangement of the batteries has been performed. Simulations have been conducted for the constant air veloc...
Abstract The amount of stored thermal energy and the stratification in the packed bed thermal ene... more Abstract The amount of stored thermal energy and the stratification in the packed bed thermal energy storage systems decrease in the afternoon because of the reduction in the solar power and solar-air heater panel's collector outlet temperature, so the charging process must be ceased at a particular instant. The optimal charging period is determined by considering the degree of stratification, energy/exergy stored, and the energy discharged during the 6 h of space heating. The proposed packed bed is divided into three sections lengthwise. Different bed materials have been placed separately in these regions regarding their volumetric heat capacity to promote stratification and sensible heat storage during charging. The bed's stratification level is determined via an exergy analysis to evaluate the discharge efficiency of the bed. The particle diameter and discharge air velocity on the system's thermal and hydrodynamic performance are inspected. The fan energy consumption during the discharge process is evaluated in the analyses. Distinctively, the air velocity is varied to obtain a minimum heat load of 18 kW for 6 h discharge process. A transient, one-dimensional finite-difference model is developed and validated with an experimental study conducted in the literature. Thermal energy storage and the stratification level are improved thanks to segmented bed by 85% and 135%, respectively.
Abstract Dimensionless entropy generation number in the microchannel condenser of a vapor compres... more Abstract Dimensionless entropy generation number in the microchannel condenser of a vapor compression refrigeration cycle is investigated. An air cooled, brazed aluminum parallel flow heat exchanger is considered as the condenser with R-134a as the refrigerant. While the effects of the fin pitch, fin height, louver angle and the air mass flow rate are investigated for the air side, the effect of the channel diameter is examined for the refrigerant side. The analysis is performed segment by segment for the superheated, two phase and subcooled regions using well-established empirical correlations. A mapping study is presented for the variation of entropy generation number with the mentioned parameters. The optimum air mass flow rate interval is found to be between 0.055 and 0.1 kgs − 1 for a given fin pitch interval of 1–1.6 mm. This range is within the operating limits of air fans in the market for this size. In this operating range, the optimal dimensions giving the minimum entropy generation numbers are presented. The entropy generation number distribution is given based on the pressure drop, heat transfer or the refrigerant state in the heat exchanger considering superheated, two phase, and subcooled regions. The entropy generation number due to pressure drop on the air side becomes dominant after a mass flow rate around 0.08 kgs − 1 . Hence, an optimum air mass flow rate generating the minimum entropy generation number is sought for different sizes of the condenser. The condenser length is variable in the range of 84.3–80.6 mm for the mentioned optimal air mass flow rate interval. The condenser height changes depending on desired operational conditions, and it is determined to be 112.5 mm for the fixed values given in the study. The study is unique in the literature in pursuing an entropy generation number mapping study for microchannel two-phase flow in air cooled heat exchangers.
Parametric analysis and dimensional optimization study for the melting process of the phase chang... more Parametric analysis and dimensional optimization study for the melting process of the phase changing
material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store
the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day
in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2
) in Antalya is taken as a reference
value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort
temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to
satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm
is implemented in MATLAB environment. The numerical model is validated for the same conditions and the
dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the
problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter
“performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between
the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this
algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the
effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting
characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K),
the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that
10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.
Parametric analysis and dimensional optimization study for the melting process of the phase chang... more Parametric analysis and dimensional optimization study for the melting process of the phase changing material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2) in Antalya is taken as a reference value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm is implemented in MATLAB environment. The numerical model is validated for the same conditions and the dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter “performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K), the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that 10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.
The amount of stored thermal energy and the stratification in the packed bed thermal energy stora... more The amount of stored thermal energy and the stratification in the packed bed thermal energy storage systems decrease in the afternoon because of the reduction in the solar power and solar-air heater panel's collector outlet temperature, so the charging process must be ceased at a particular instant. The optimal charging period is determined by considering the degree of stratification, energy/exergy stored, and the energy discharged during the 6 h of space heating. The proposed packed bed is divided into three sections lengthwise. Different bed materials have been placed separately in these regions regarding their volumetric heat capacity to promote stratification and sensible heat storage during charging. The bed's stratification level is determined via an exergy analysis to evaluate the discharge efficiency of the bed. The particle diameter and discharge air velocity on the system's thermal and hydrodynamic performance are inspected. The fan energy consumption during the discharge process is evaluated in the analyses. Distinctively, the air velocity is varied to obtain a minimum heat load of 18 kW for 6 h discharge process. A transient, one-dimensional finite-difference model is developed and validated with an experimental study conducted in the literature. Thermal energy storage and the stratification level are improved thanks to segmented bed by 85% and 135%, respectively.
Dimensionless entropy generation number in the microchannel condenser of a vapor compression refr... more Dimensionless entropy generation number in the microchannel condenser of a vapor compression refrigeration cycle is investigated. An air cooled, brazed aluminum parallel flow heat exchanger is considered as the condenser with R-134a as the refrigerant. While the effects of the fin pitch, fin height, louver angle and the air mass flow rate are investigated for the air side, the effect of the channel diameter is examined for the refrigerant side. The analysis is performed segment by segment for the superheated, two phase and subcooled regions using well-established empirical correlations. A mapping study is presented for the variation of entropy generation number with the mentioned parameters. The optimum air mass flow rate interval is found to be between 0.055 and 0 1 1. kgs − for a given fin pitch interval of 1–1.6 mm. This range is within the operating limits of air fans in the market for this size. In this operating range, the optimal dimensions giving the minimum entropy generation numbers are presented. The entropy generation number distribution is given based on the pressure drop, heat transfer or the refrigerant state in the heat exchanger considering superheated, two phase, and subcooled regions. The entropy generation number due to pressure drop on the air side becomes dominant after a mass flow rate around 0 08 1. kgs −. Hence, an optimum air mass flow rate generating the minimum entropy generation number is sought for different sizes of the condenser. The condenser length is variable in the range of 84.3–80.6 mm for the mentioned optimal air mass flow rate interval. The condenser height changes depending on desired operational conditions, and it is determined to be 112.5 mm for the fixed values given in the study. The study is unique in the literature in pursuing an entropy generation number mapping study for microchannel two-phase flow in air cooled heat exchangers.
Dimensional optimization of silicon microchannel heat sinks is performed by minimizing the total ... more Dimensional optimization of silicon microchannel heat sinks is performed by minimizing the total thermal resistance. Intel Core i7-900 Desktop Processor of chip core dimensions of 1.891 cm × 1.44 cm is considered as a reference processor which is reported to dissipate 130 W of heat. The properties are evaluated at the area weighted average of the fluid inlet and iteratively calculated outlet temperatures. The effects of the thermal and hydrodynamic entrance regions on heat transfer and flow are also investigated. The study is unique in that the optimization has been performed for localized multiple heat sources, as well as for a uniform heat load condition. The results of the optimization agreed very well with available ones in the literature.► Analytical optimization of microchannel heat sink dimensions by thermal resistance minimization. ► Effects of hot spots in multiple local heat sources are included. ► Effects of the hydrodynamic and thermal entry regions, and property variations are considered. ► Intel Core i7-900 Desktop Processor is the reference processor. ► A wider range of pumping powers and temperatures are handled compared to the optimization studies available in the literature.
A parametric analysis has been conducted for the phase change material (PCM)-air cooled battery p... more A parametric analysis has been conducted for the phase change material (PCM)-air cooled battery pack. The system is composed of 26650 lithium-ion LiFePO4 batteries enclosed by PCM. A one-dimensional thermal model for the PCM domain is developed using the enthalpy method. The finite volume method is employed to solve the energy equation for both cell and PCM domain. The developed computational algorithm has been validated as a result of the simulations for the same conditions with the literature. The discharge process of the batteries has been investigated for 2C, 3C, and 5C rates. Thermal analyses have been performed for passive (natural convection) and active cooling (forced convection). It is aimed to keep the temperature of the battery cell under critical levels. A parametric investigation for crucial parameters like PCM layer thickness, the thermal conductivity of the PCM, arrangement of the batteries has been performed. Simulations have been conducted for the constant air veloc...
Abstract The amount of stored thermal energy and the stratification in the packed bed thermal ene... more Abstract The amount of stored thermal energy and the stratification in the packed bed thermal energy storage systems decrease in the afternoon because of the reduction in the solar power and solar-air heater panel's collector outlet temperature, so the charging process must be ceased at a particular instant. The optimal charging period is determined by considering the degree of stratification, energy/exergy stored, and the energy discharged during the 6 h of space heating. The proposed packed bed is divided into three sections lengthwise. Different bed materials have been placed separately in these regions regarding their volumetric heat capacity to promote stratification and sensible heat storage during charging. The bed's stratification level is determined via an exergy analysis to evaluate the discharge efficiency of the bed. The particle diameter and discharge air velocity on the system's thermal and hydrodynamic performance are inspected. The fan energy consumption during the discharge process is evaluated in the analyses. Distinctively, the air velocity is varied to obtain a minimum heat load of 18 kW for 6 h discharge process. A transient, one-dimensional finite-difference model is developed and validated with an experimental study conducted in the literature. Thermal energy storage and the stratification level are improved thanks to segmented bed by 85% and 135%, respectively.
Abstract Dimensionless entropy generation number in the microchannel condenser of a vapor compres... more Abstract Dimensionless entropy generation number in the microchannel condenser of a vapor compression refrigeration cycle is investigated. An air cooled, brazed aluminum parallel flow heat exchanger is considered as the condenser with R-134a as the refrigerant. While the effects of the fin pitch, fin height, louver angle and the air mass flow rate are investigated for the air side, the effect of the channel diameter is examined for the refrigerant side. The analysis is performed segment by segment for the superheated, two phase and subcooled regions using well-established empirical correlations. A mapping study is presented for the variation of entropy generation number with the mentioned parameters. The optimum air mass flow rate interval is found to be between 0.055 and 0.1 kgs − 1 for a given fin pitch interval of 1–1.6 mm. This range is within the operating limits of air fans in the market for this size. In this operating range, the optimal dimensions giving the minimum entropy generation numbers are presented. The entropy generation number distribution is given based on the pressure drop, heat transfer or the refrigerant state in the heat exchanger considering superheated, two phase, and subcooled regions. The entropy generation number due to pressure drop on the air side becomes dominant after a mass flow rate around 0.08 kgs − 1 . Hence, an optimum air mass flow rate generating the minimum entropy generation number is sought for different sizes of the condenser. The condenser length is variable in the range of 84.3–80.6 mm for the mentioned optimal air mass flow rate interval. The condenser height changes depending on desired operational conditions, and it is determined to be 112.5 mm for the fixed values given in the study. The study is unique in the literature in pursuing an entropy generation number mapping study for microchannel two-phase flow in air cooled heat exchangers.
Parametric analysis and dimensional optimization study for the melting process of the phase chang... more Parametric analysis and dimensional optimization study for the melting process of the phase changing
material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store
the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day
in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2
) in Antalya is taken as a reference
value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort
temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to
satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm
is implemented in MATLAB environment. The numerical model is validated for the same conditions and the
dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the
problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter
“performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between
the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this
algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the
effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting
characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K),
the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that
10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.
Parametric analysis and dimensional optimization study for the melting process of the phase chang... more Parametric analysis and dimensional optimization study for the melting process of the phase changing material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2) in Antalya is taken as a reference value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm is implemented in MATLAB environment. The numerical model is validated for the same conditions and the dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter “performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K), the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that 10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.
The amount of stored thermal energy and the stratification in the packed bed thermal energy stora... more The amount of stored thermal energy and the stratification in the packed bed thermal energy storage systems decrease in the afternoon because of the reduction in the solar power and solar-air heater panel's collector outlet temperature, so the charging process must be ceased at a particular instant. The optimal charging period is determined by considering the degree of stratification, energy/exergy stored, and the energy discharged during the 6 h of space heating. The proposed packed bed is divided into three sections lengthwise. Different bed materials have been placed separately in these regions regarding their volumetric heat capacity to promote stratification and sensible heat storage during charging. The bed's stratification level is determined via an exergy analysis to evaluate the discharge efficiency of the bed. The particle diameter and discharge air velocity on the system's thermal and hydrodynamic performance are inspected. The fan energy consumption during the discharge process is evaluated in the analyses. Distinctively, the air velocity is varied to obtain a minimum heat load of 18 kW for 6 h discharge process. A transient, one-dimensional finite-difference model is developed and validated with an experimental study conducted in the literature. Thermal energy storage and the stratification level are improved thanks to segmented bed by 85% and 135%, respectively.
Dimensionless entropy generation number in the microchannel condenser of a vapor compression refr... more Dimensionless entropy generation number in the microchannel condenser of a vapor compression refrigeration cycle is investigated. An air cooled, brazed aluminum parallel flow heat exchanger is considered as the condenser with R-134a as the refrigerant. While the effects of the fin pitch, fin height, louver angle and the air mass flow rate are investigated for the air side, the effect of the channel diameter is examined for the refrigerant side. The analysis is performed segment by segment for the superheated, two phase and subcooled regions using well-established empirical correlations. A mapping study is presented for the variation of entropy generation number with the mentioned parameters. The optimum air mass flow rate interval is found to be between 0.055 and 0 1 1. kgs − for a given fin pitch interval of 1–1.6 mm. This range is within the operating limits of air fans in the market for this size. In this operating range, the optimal dimensions giving the minimum entropy generation numbers are presented. The entropy generation number distribution is given based on the pressure drop, heat transfer or the refrigerant state in the heat exchanger considering superheated, two phase, and subcooled regions. The entropy generation number due to pressure drop on the air side becomes dominant after a mass flow rate around 0 08 1. kgs −. Hence, an optimum air mass flow rate generating the minimum entropy generation number is sought for different sizes of the condenser. The condenser length is variable in the range of 84.3–80.6 mm for the mentioned optimal air mass flow rate interval. The condenser height changes depending on desired operational conditions, and it is determined to be 112.5 mm for the fixed values given in the study. The study is unique in the literature in pursuing an entropy generation number mapping study for microchannel two-phase flow in air cooled heat exchangers.
Dimensional optimization of silicon microchannel heat sinks is performed by minimizing the total ... more Dimensional optimization of silicon microchannel heat sinks is performed by minimizing the total thermal resistance. Intel Core i7-900 Desktop Processor of chip core dimensions of 1.891 cm × 1.44 cm is considered as a reference processor which is reported to dissipate 130 W of heat. The properties are evaluated at the area weighted average of the fluid inlet and iteratively calculated outlet temperatures. The effects of the thermal and hydrodynamic entrance regions on heat transfer and flow are also investigated. The study is unique in that the optimization has been performed for localized multiple heat sources, as well as for a uniform heat load condition. The results of the optimization agreed very well with available ones in the literature.► Analytical optimization of microchannel heat sink dimensions by thermal resistance minimization. ► Effects of hot spots in multiple local heat sources are included. ► Effects of the hydrodynamic and thermal entry regions, and property variations are considered. ► Intel Core i7-900 Desktop Processor is the reference processor. ► A wider range of pumping powers and temperatures are handled compared to the optimization studies available in the literature.
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Papers by Göker Türkakar
material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store
the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day
in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2
) in Antalya is taken as a reference
value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort
temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to
satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm
is implemented in MATLAB environment. The numerical model is validated for the same conditions and the
dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the
problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter
“performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between
the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this
algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the
effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting
characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K),
the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that
10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.
material placed in cold energy storage devices have been conducted. Phase changing material, PCM, is used to store
the cold energy. A cross-flow tubular PCM-air heat exchanger is used. An electricity peak shaving for a summer day
in Antalya for 5 hours (10:00-15:00) is aimed. The cooling load of a room (33 m2
) in Antalya is taken as a reference
value. A minimum cooling load of 2850 W is supplied throughout 5 hours to maintain the building's comfort
temperature. Contrary to the studies handling air velocity constant, it is varied during melting in the present study to
satisfy the minimum cooling load. The melting process is analyzed using a numerical model. A computational algorithm
is implemented in MATLAB environment. The numerical model is validated for the same conditions and the
dimensions with an analytical model presented in the literature. A transient analysis has been employed, and the
problem is discretized for the time and space domain. A dimensional optimization algorithm is employed. A parameter
“performance ratio/ cooling index”, the ratio of total cooling to fan energy consumption, is defined. Spacing between
the tubes giving the maximum performance ratio is sought for aligned and staggered tube bank arrangements using this
algorithm. The best performance ratio is obtained at 0.2 m/s initial velocities for both arrangements. In addition, the
effect of sizing/arrangement of the tubes, PCM mass, and thermal conductivity of the PCM on the melting
characteristics is investigated. As a result of increasing the thermal conductivity from 0.2 W/(m·K) to 0.6 W/(m·K),
the performance ratios are raised 4.58 and 3.52 times for aligned and staggered orders, respectively. It is calculated that
10 kg PCM can be saved thanks to enhancing the thermal conductivity of the PCM.