Improving heat exchange intensity is a major goal in the heat exchanger industry. The use of baffles is one of the techniques employed to achieve this goal. In this numerical work, the effect of an inward-facing baffle placed on the wall of a cylindrical horizontal pipe is treated for the case of nanofluid. A sequential analysis is offered to better understand the different effects and their consequences, particularly on the average exchange rate, in addition to somewhat filling the gap identified in the literature for the case of nanofluid with various shapes of the baffle. The study, divided into three parts, begins for 10Re250 with the case of pipe without baffle, where the water-based nanofluid effect is treated. Three types of nanoparticles (Cu, Al2O3 and TiO3) at volume concentration 0ϕ10% are considered. An insulated primary pipe is placed to ensure dynamic establishment at the entrance to the heating pipe assumed to be under imposed temperature. The results showed the clear effects of modifying the kinematic viscosity and thermal diffusivity on the dynamic and thermal lengths respectively with the addition of nanoparticles compared to the base fluid. Correlations are proposed for their determination. A heat exchange rate that improves as the volume concentration increases is recorded, particularly for nanoparticles with high thermal conductivity. In the second part, a rectangular baffle is assumed in the heated pipe, where the effects of its position, length and width are analyzed respectively. The results showed a greater interest in placing the baffle close to the entrance, especially if it is longer. In the last part of the work, three other shapes of the baffle are proposed (Trapezoidal, Triangular and Elliptical). The results confirm that the non-smooth shape of the baffle creates more disturbances in the dynamic and thermal fields, and therefore a greater improvement in the heat exchange rate. For the last two parts, the nanofluid effect remains similar to that recorded for pipe without baffle.
{"title":"Effect of an inward-facing baffle on the laminar forced convection heating along a cylindrical horizontal pipe for different nanofluids","authors":"Horimek Abderrahmane, Aicha Oueld-M’barek, Mohamed Sadeddine","doi":"10.1615/heattransres.2024051837","DOIUrl":"https://doi.org/10.1615/heattransres.2024051837","url":null,"abstract":"Improving heat exchange intensity is a major goal in the heat exchanger industry. The use of baffles is one of the techniques employed to achieve this goal. In this numerical work, the effect of an inward-facing baffle placed on the wall of a cylindrical horizontal pipe is treated for the case of nanofluid. A sequential analysis is offered to better understand the different effects and their consequences, particularly on the average exchange rate, in addition to somewhat filling the gap identified in the literature for the case of nanofluid with various shapes of the baffle. The study, divided into three parts, begins for 10Re250 with the case of pipe without baffle, where the water-based nanofluid effect is treated. Three types of nanoparticles (Cu, Al2O3 and TiO3) at volume concentration 0ϕ10% are considered. An insulated primary pipe is placed to ensure dynamic establishment at the entrance to the heating pipe assumed to be under imposed temperature. The results showed the clear effects of modifying the kinematic viscosity and thermal diffusivity on the dynamic and thermal lengths respectively with the addition of nanoparticles compared to the base fluid. Correlations are proposed for their determination. A heat exchange rate that improves as the volume concentration increases is recorded, particularly for nanoparticles with high thermal conductivity. In the second part, a rectangular baffle is assumed in the heated pipe, where the effects of its position, length and width are analyzed respectively. The results showed a greater interest in placing the baffle close to the entrance, especially if it is longer. In the last part of the work, three other shapes of the baffle are proposed (Trapezoidal, Triangular and Elliptical). The results confirm that the non-smooth shape of the baffle creates more disturbances in the dynamic and thermal fields, and therefore a greater improvement in the heat exchange rate. For the last two parts, the nanofluid effect remains similar to that recorded for pipe without baffle.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"43 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140882698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Experimental investigation of the thermo-hydraulic and exergetic performance of a heat exchanger with three fluids (HEFT) was carried out in the present work. The HEFT comprises of two straight tubes and a helical tube inserted in between the outermost and the innermost tube for better heat transfer. The present heat exchanger is projected for heating of two fluids (TF2: normal water and TF3: air) simultaneously by another fluid TF1 (hot water). During the examination, three levels of TF1 flow rate (i.e., 100, 200, and 300 LPH), three levels of TF2 flow rate (i.e.,50, 100, and 150 LPH), three levels of TF3 flow velocity (i.e., 1, 2, and 3 m/s, and two levels of TF1inlet temperature (i.e., 60, and 80 degrees Celsius) are maintained. A coupled Taguchi-Grey relational analysis is employed to determine the optimum combination of control parameters to forecast optimized overall performances. The outcomes show that, the inlet temperature of TF1 is forecasted as the most decisive factor for the JF factor, exergy efficiency, and sustainability index with a contribution of 41.29%, 63.06%, and 60.66% respectively. The optimized performance of the HEFT is forecasted at 60℃ inlet temperature of TF1, 100 LPH flow rate of TF1, 150 LPH flow rate of TF2, and 3 m/s velocity of TF3 and confirmed with significant enhancement in Grey relational grade of 32.9%.
{"title":"Enhancement and optimization of thermo-hydraulic characteristics of a heat exchanger with three fluids used in sustainable heating applications","authors":"Vikas Bargah, Sudhansu Mishra, Belal Almasri, Taraprasad Mohapatra","doi":"10.1615/heattransres.2024052334","DOIUrl":"https://doi.org/10.1615/heattransres.2024052334","url":null,"abstract":"Experimental investigation of the thermo-hydraulic and exergetic performance of a heat exchanger with three fluids (HEFT) was carried out in the present work. The HEFT comprises of two straight tubes and a helical tube inserted in between the outermost and the innermost tube for better heat transfer. The present heat exchanger is projected for heating of two fluids (TF2: normal water and TF3: air) simultaneously by another fluid TF1 (hot water). During the examination, three levels of TF1 flow rate (i.e., 100, 200, and 300 LPH), three levels of TF2 flow rate (i.e.,50, 100, and 150 LPH), three levels of TF3 flow velocity (i.e., 1, 2, and 3 m/s, and two levels of TF1inlet temperature (i.e., 60, and 80 degrees Celsius) are maintained. A coupled Taguchi-Grey relational analysis is employed to determine the optimum combination of control parameters to forecast optimized overall performances. The outcomes show that, the inlet temperature of TF1 is forecasted as the most decisive factor for the JF factor, exergy efficiency, and sustainability index with a contribution of 41.29%, 63.06%, and 60.66% respectively. The optimized performance of the HEFT is forecasted at 60℃ inlet temperature of TF1, 100 LPH flow rate of TF1, 150 LPH flow rate of TF2, and 3 m/s velocity of TF3 and confirmed with significant enhancement in Grey relational grade of 32.9%.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"49 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141146618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-01DOI: 10.1615/heattransres.2024052690
Ummid Shaikh, Dhanapal Kamble, Sandeep Kore
The thermal behavior of Lithium-ion battery pack has a substantial impact on its cycle life, charge-discharge characteristics, and safety. This research presents a comparative experimental analysis of the thermal performance of a lithium-ion battery pack designed for an electric bike, both with and without the use of phase change material (PCM). In both cases, a novel approach of passing air over the casing of the battery pack is employed to induce natural and forced convection conditions, ensuring compliance with IP67 standards. The study examines the temporal variation of battery pack temperature under various constant discharge rates. The study demonstrated that the forced convection cooling method was more effective in maintaining the maximum temperature (Tmax) of the battery pack below the optimal and safe temperature limits as compared to the natural convection cooling method in the absence of phase change materials (PCM). With the incorporation of PCM, the Tmax was found to be 24.6% lower than the baseline case. Furthermore, the temperature homogeneity within the battery pack was significantly enhanced, as the maximum temperature difference (ΔTmax) was reduced by 61% compared to the baseline case. The combination of natural cooling and PCM is found to be the most effective at 0.75C discharge.
{"title":"Enhancing Thermal performance of Lithium-Ion Battery Pack by integrating Phase Change Material with Convective Surface Cooling Technique for Electric Bike Application","authors":"Ummid Shaikh, Dhanapal Kamble, Sandeep Kore","doi":"10.1615/heattransres.2024052690","DOIUrl":"https://doi.org/10.1615/heattransres.2024052690","url":null,"abstract":"The thermal behavior of Lithium-ion battery pack has a substantial impact on its cycle life, charge-discharge characteristics, and safety. This research presents a comparative experimental analysis of the thermal performance of a lithium-ion battery pack designed for an electric bike, both with and without the use of phase change material (PCM). In both cases, a novel approach of passing air over the casing of the battery pack is employed to induce natural and forced convection conditions, ensuring compliance with IP67 standards. The study examines the temporal variation of battery pack temperature under various constant discharge rates.\u0000The study demonstrated that the forced convection cooling method was more effective in maintaining the maximum temperature (Tmax) of the battery pack below the optimal and safe temperature limits as compared to the natural convection cooling method in the absence of phase change materials (PCM). With the incorporation of PCM, the Tmax was found to be 24.6% lower than the baseline case. Furthermore, the temperature homogeneity within the battery pack was significantly enhanced, as the maximum temperature difference (ΔTmax) was reduced by 61% compared to the baseline case. The combination of natural cooling and PCM is found to be the most effective at 0.75C discharge.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"23 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141166762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1615/heattransres.2024051450
Dahmani Mourad, Ferahta Fatima Zohra
In a three-dimensional study, numerical simulations were carried out to quantify the natural convection heat transfer occurring within the air gap between the absorber and the glass cover of a thermal solar collector. The study explored various combinations of partition placement and spacing: partitions glued under the glass cover [PGG Model], partitions glued at absorber [PGA Model] and partitions suspended between the absorber plate and glass cover [PS Model]. Simulations were conducted with two partition spacing configurations of 0.14m and 0.1m. The primary aim was to identify cost-effective methods for reducing heat losses due to natural convection in the air gap while achieving higher absorption temperatures. The findings revealed that using a partition spacing of 1.4m resulted in complex and unstable outcomes, making comparisons between models difficult. However, decreasing the partition spacing to 0.1m enhanced convective resistance, fostering temperature stability within the cavity. Nevertheless, the PGA Model transitioned from unstable to stable flow, resulting in a notable temperature rise, making it the most effective configuration. Additionally, the PGG Model configuration exhibited promising performance. Meanwhile, the PS Model experienced quasi-periodic cooling due to undulating flow patterns. This study emphasizes the importance of balancing uniform heating and stable flow in collector systems, underscoring the necessity for comprehensive 3-D analyses. Adjustments to partition placement and spacing can greatly enhance solar collector design.
{"title":"Enhancing convective heat loss reduction in flat plate solar collectors by optimal integration of transparent partitions in the air gap.","authors":"Dahmani Mourad, Ferahta Fatima Zohra","doi":"10.1615/heattransres.2024051450","DOIUrl":"https://doi.org/10.1615/heattransres.2024051450","url":null,"abstract":"In a three-dimensional study, numerical simulations were carried out to quantify the natural convection heat transfer occurring within the air gap between the absorber and the glass cover of a thermal solar collector. The study explored various combinations of partition placement and spacing: partitions glued under the glass cover [PGG Model], partitions glued at absorber [PGA Model] and partitions suspended between the absorber plate and glass cover [PS Model]. Simulations were conducted with two partition spacing configurations of 0.14m and 0.1m. The primary aim was to identify cost-effective methods for reducing heat losses due to natural convection in the air gap while achieving higher absorption temperatures. The findings revealed that using a partition spacing of 1.4m resulted in complex and unstable outcomes, making comparisons between models difficult. However, decreasing the partition spacing to 0.1m enhanced convective resistance, fostering temperature stability within the cavity. Nevertheless, the PGA Model transitioned from unstable to stable flow, resulting in a notable temperature rise, making it the most effective configuration. Additionally, the PGG Model configuration exhibited promising performance. Meanwhile, the PS Model experienced quasi-periodic cooling due to undulating flow patterns. This study emphasizes the importance of balancing uniform heating and stable flow in collector systems, underscoring the necessity for comprehensive 3-D analyses. Adjustments to partition placement and spacing can greatly enhance solar collector design.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"3 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140616086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1615/heattransres.2024052886
Frans Coetzee, Gazi Mahmood
Experiments of the heat transfer and pressure drop are performed in a rectangular channel employing eight different arrays of cylindrical cross-bars as inserts. Numerical simulations are also performed to examine the secondary flow caused by the cylinders. The objectives are to investigate the enhancement of the channel-wall heat transfer and pressure drop caused by the local flow, cylinder array geometry, and flow Reynolds number. Two different cylinder diameters of 1.0 mm and 2.0 mm are employed. The diameter of 2.0 mm is used to create four in-line arrays while the diameter of 1.0 mm is used to create four staggered arrays of the cylinders. The cylinder arrays employ different diameter-to-pitch ratios (0.025 to 0.2) and cylinder orientations (45°, 90°) relative to the main flow direction. The flow Reynolds number is varied between 600 and 13000. Only two array geometries, one in-line and one staggered, with the cylinders oriented at 90° to the flow are modelled for the numerical study. The numerical results show the local flow accelerates in the gap between the cylinder and channel wall. The vortex shedding downstream of the cylinders interacts with the channel wall. The Nusselt number on the channel wall and friction factor are measured with and without the cylinders. The ratios of Nusselt numbers and friction factors increase with the Reynolds number when the Reynolds number is less than 3000. The ratios always increase with the diameter-to-pitch ratio.
{"title":"Cylindrical Cross-Bars for Thermal Performance Augmentation in Air Channel","authors":"Frans Coetzee, Gazi Mahmood","doi":"10.1615/heattransres.2024052886","DOIUrl":"https://doi.org/10.1615/heattransres.2024052886","url":null,"abstract":"Experiments of the heat transfer and pressure drop are performed in a rectangular channel employing eight different arrays of cylindrical cross-bars as inserts. Numerical simulations are also performed to examine the secondary flow caused by the cylinders. The objectives are to investigate the enhancement of the channel-wall heat transfer and pressure drop caused by the local flow, cylinder array geometry, and flow Reynolds number. Two different cylinder diameters of 1.0 mm and 2.0 mm are employed. The diameter of 2.0 mm is used to create four in-line arrays while the diameter of 1.0 mm is used to create four staggered arrays of the cylinders. The cylinder arrays employ different diameter-to-pitch ratios (0.025 to 0.2) and cylinder orientations (45°, 90°) relative to the main flow direction. The flow Reynolds number is varied between 600 and 13000. Only two array geometries, one in-line and one staggered, with the cylinders oriented at 90° to the flow are modelled for the numerical study. The numerical results show the local flow accelerates in the gap between the cylinder and channel wall. The vortex shedding downstream of the cylinders interacts with the channel wall. The Nusselt number on the channel wall and friction factor are measured with and without the cylinders. The ratios of Nusselt numbers and friction factors increase with the Reynolds number when the Reynolds number is less than 3000. The ratios always increase with the diameter-to-pitch ratio.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"17 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1615/heattransres.2024049994
Andaç Batur Çolak
The phenomenon of natural convection, which is widely used in nature and engineering applications, is a current issue that can be encountered in every field of daily life. In this study, the natural convection characteristics of a complex liquid containing nanoparticles and gyrotactic microorganisms in a heated square cavity were investigated using a machine learning approach. Nusselt number, average Sherwood number of nanoparticles and average Sherwood number of microorganisms were considered as natural convection parameters and an artificial neural network model was developed to estimate these values. Lewis number, Brownian motion parameter, thermophoresis parameter and buoyancy ratio parameter values were defined as input parameters in the network model, which has a multi-layer perceptron architecture developed with a total of 24 data sets. There were 10 neurons in the hidden layer of the network model, which has a Bayesian regularization training algorithm. The outputs obtained from the network model were compared with the target values, in addition, the prediction performance of the model was extensively analyzed using various performance parameters. It was seen that the predicted values obtained from the neural network and the target values were in an ideal harmony. On the other hand, the coefficient of determination value for the network model was 0.99999% and the mean deviation rates were lower than -0.03%. The results of the study showed that the developed neural network model can predict the natural convection parameters discussed with high accuracy.
{"title":"Modeling the Influence of Nanoparticles and Gyrotactic Microorganisms on Natural Convection in a Heated Square Cavity: A New Machine-Learning Study","authors":"Andaç Batur Çolak","doi":"10.1615/heattransres.2024049994","DOIUrl":"https://doi.org/10.1615/heattransres.2024049994","url":null,"abstract":"The phenomenon of natural convection, which is widely used in nature and engineering applications, is a current issue that can be encountered in every field of daily life. In this study, the natural convection characteristics of a complex liquid containing nanoparticles and gyrotactic microorganisms in a heated square cavity were investigated using a machine learning approach. Nusselt number, average Sherwood number of nanoparticles and average Sherwood number of microorganisms were considered as natural convection parameters and an artificial neural network model was developed to estimate these values. Lewis number, Brownian motion parameter, thermophoresis parameter and buoyancy ratio parameter values were defined as input parameters in the network model, which has a multi-layer perceptron architecture developed with a total of 24 data sets. There were 10 neurons in the hidden layer of the network model, which has a Bayesian regularization training algorithm. The outputs obtained from the network model were compared with the target values, in addition, the prediction performance of the model was extensively analyzed using various performance parameters. It was seen that the predicted values obtained from the neural network and the target values were in an ideal harmony. On the other hand, the coefficient of determination value for the network model was 0.99999% and the mean deviation rates were lower than -0.03%. The results of the study showed that the developed neural network model can predict the natural convection parameters discussed with high accuracy.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"177 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140588077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Increasing the ratio of the internal and external surface areas of heat exchangers is ordinarily considered to be an effective way of improving performance. In this paper a novel finless heat exchanger with mini-diameter tubes used as air heater or air cooler is proposed. In order to fully understand the performance of this novel type of heat exchanger, a test bench was established. The heating and cooling performances were tested according to relevant standard specifications. Furthermore, the heat exchanger was compared with seven conventional heat exchangers. This novel heat exchanger has excellent surface heat transfer temperature difference uniformity. Relative to the seven traditional heat exchangers examined, this novel design demonstrated remarkable heat transfer enhancements, registering gains of at least 173% as an air heater and a staggering 277% as an air cooler. However, it also exhibited elevated water-side flow resistances. Critically, conventional empirical heat transfer equations proved suboptimal for this system, necessitating modifications that yielded new coefficients: C=0.0839 and n=0.992.
{"title":"Experimental Investigation on the Application Potential of Finless Heat Exchanger with Mini-Diameter Tubes Utilized as Air Heater or Air Cooler","authors":"Binfei Zhan, Zhichao Wang, Shuangquan Shao, Zhaowei Xu, Jiandong Li, Jing Yan, Lichao Han","doi":"10.1615/heattransres.2024050344","DOIUrl":"https://doi.org/10.1615/heattransres.2024050344","url":null,"abstract":"Increasing the ratio of the internal and external surface areas of heat exchangers is ordinarily considered to be an effective way of improving performance. In this paper a novel finless heat exchanger with mini-diameter tubes used as air heater or air cooler is proposed. In order to fully understand the performance of this novel type of heat exchanger, a test bench was established. The heating and cooling performances were tested according to relevant standard specifications. Furthermore, the heat exchanger was compared with seven conventional heat exchangers. This novel heat exchanger has excellent surface heat transfer temperature difference uniformity. Relative to the seven traditional heat exchangers examined, this novel design demonstrated remarkable heat transfer enhancements, registering gains of at least 173% as an air heater and a staggering 277% as an air cooler. However, it also exhibited elevated water-side flow resistances. Critically, conventional empirical heat transfer equations proved suboptimal for this system, necessitating modifications that yielded new coefficients: C=0.0839 and n=0.992.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"31 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140588602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1615/heattransres.2024052326
Jinglong WANG, Lin Lu
Solar thermoelectric generator (STEG) has been widely studied in optical and thermal concentrating fields, and the spectral properties are mainly focused on the solar spectrum. However, limited attention has been paid to STEG without any concentrators and in the full spectral range. Therefore, in this work, a thermal-electrical coupled mathematical model for STEG systems is developed according to thermal resistance networks to investigate heat losses above the absorber and power generation performance. For the ideal selective absorber and emitter system, the main heat losses from the absorber occur due to radiative cooling to the sky as well as for the ideal broadband absorber system, as opposed to convection and ambient radiative losses. These sky radiative cooling losses account for approximately 83.8% and 73.7% of the total heat losses, respectively. The total water vapor has the greatest impact on radiative cooling power compared to other forms of heat loss, while wind speed has the largest effect on convective heat loss. Elevated ambient temperatures result in decreased heat loss across all forms. An increase in bottom surface temperature or solar irradiance results in an increase in various forms of heat loss. In light of its cost-effectiveness and environmentally-friendly characteristics, this paper offers recommendations on enhancing the system design of STEG aiming to minimize heat loss, enhance system performance, and pave the way for a promising future in various applications.
{"title":"Evaluation of Heat losses in a non-concentrated solar thermoelectric generator with spectrally selective absorbers","authors":"Jinglong WANG, Lin Lu","doi":"10.1615/heattransres.2024052326","DOIUrl":"https://doi.org/10.1615/heattransres.2024052326","url":null,"abstract":"Solar thermoelectric generator (STEG) has been widely studied in optical and thermal concentrating fields, and the spectral properties are mainly focused on the solar spectrum. However, limited attention has been paid to STEG without any concentrators and in the full spectral range. Therefore, in this work, a thermal-electrical coupled mathematical model for STEG systems is developed according to thermal resistance networks to investigate heat losses above the absorber and power generation performance. For the ideal selective absorber and emitter system, the main heat losses from the absorber occur due to radiative cooling to the sky as well as for the ideal broadband absorber system, as opposed to convection and ambient radiative losses. These sky radiative cooling losses account for approximately 83.8% and 73.7% of the total heat losses, respectively. The total water vapor has the greatest impact on radiative cooling power compared to other forms of heat loss, while wind speed has the largest effect on convective heat loss. Elevated ambient temperatures result in decreased heat loss across all forms. An increase in bottom surface temperature or solar irradiance results in an increase in various forms of heat loss. In light of its cost-effectiveness and environmentally-friendly characteristics, this paper offers recommendations on enhancing the system design of STEG aiming to minimize heat loss, enhance system performance, and pave the way for a promising future in various applications.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"55 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140804465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1615/heattransres.2024051829
Xuesong Zhang, Jun Wang, Zhiwei Wu, Xiaolin Li, Wenxiang Cao
The application of phase change material (PCM) in energy storage systems is limited by its low thermal conductivity. One of the effective methods to improve the thermal conductivity of PCM is to embed foam metal within it. To investigate the effects of foam metal infill position and porosity on the melting process and temperature distribution of PCM, a visualized experimental system study is built. Paraffin is employed as the PCM with a melting point of 62°C, while 85%, 90%, and 95% porosity copper foam are chosen in the experiment. The evolution of the liquid-solid phase interface and the temperature distribution in the PCM are recorded. Single-layer filling schemes show that placing copper foam closer to the bottom accelerates melting, while double-layer schemes further optimize the melting time and temperature distribution. Additionally, decreasing the porosity of copper foam enhances heat transfer, shortening melting times. The study introduces a melt efficiency index, demonstrating that optimizing filling schemes and porosities improves the overall melting performance. When the copper foam with 90% and 85% porosity is arranged in the middle and bottom layer, respectively, the complete melting time is shortened by 38.2% and the maximum and average temperature differences are reduced by 30.0% and 45.2%, respectively, compared with pure paraffin. The findings contribute valuable insights into designing efficient PCM systems for thermal energy storage applications, emphasizing the importance of copper foam arrangement and porosity optimization.
{"title":"Effect of Metal Foam Filling Position and Porosity on Heat Transfer of PCM: A Visualized Experimental Study","authors":"Xuesong Zhang, Jun Wang, Zhiwei Wu, Xiaolin Li, Wenxiang Cao","doi":"10.1615/heattransres.2024051829","DOIUrl":"https://doi.org/10.1615/heattransres.2024051829","url":null,"abstract":"The application of phase change material (PCM) in energy storage systems is limited by its low thermal conductivity. One of the effective methods to improve the thermal conductivity of PCM is to embed foam metal within it. To investigate the effects of foam metal infill position and porosity on the melting process and temperature distribution of PCM, a visualized experimental system study is built. Paraffin is employed as the PCM with a melting point of 62°C, while 85%, 90%, and 95% porosity copper foam are chosen in the experiment. The evolution of the liquid-solid phase interface and the temperature distribution in the PCM are recorded. Single-layer filling schemes show that placing copper foam closer to the bottom accelerates melting, while double-layer schemes further optimize the melting time and temperature distribution. Additionally, decreasing the porosity of copper foam enhances heat transfer, shortening melting times. The study introduces a melt efficiency index, demonstrating that optimizing filling schemes and porosities improves the overall melting performance. When the copper foam with 90% and 85% porosity is arranged in the middle and bottom layer, respectively, the complete melting time is shortened by 38.2% and the maximum and average temperature differences are reduced by 30.0% and 45.2%, respectively, compared with pure paraffin. The findings contribute valuable insights into designing efficient PCM systems for thermal energy storage applications, emphasizing the importance of copper foam arrangement and porosity optimization.","PeriodicalId":50408,"journal":{"name":"Heat Transfer Research","volume":"6 1","pages":""},"PeriodicalIF":1.7,"publicationDate":"2024-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140587980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-01DOI: 10.1615/heattransres.2024049821
Digvijay Ronge, Prashant Pawar
Micro Heat Sinks (MHS) are becoming integral part of microelectronics nowadays because of their ability to cool the tiny components which generate high heat flux. In this study, an electronic chip with a high heat flux of 100 W/cm² is cooled with the help of a MHS device which has repetitive patterns of obstacles of various shapes in the flow of cooling medium. Numerical modelling of all MHSs were performed using a Computational Fluid Dynamics (CFD) solver and the pattern, which gives better thermo-hydraulic performance, was selected for optimization. A parametric study was performed with various obstacle sizes, distance between obstacles and flow rate of cooling medium for maximum temperature of chip and pressure drop. Regression analysis was carried out with Response Surface Method (RSM) between these three design variables and two objective functions, viz. thermal resistance (Rth) and pumping power (Pp). A multi-objective optimization of the MHS was performed using genetic algorithm (GA) and pareto-optimal solutions were obtained. An optimal design was fabricated and the cooling experiment was carried out under optimal flow conditions. The repetitive pattern of obstacles increases the conjugate heat transfer area and helps in improving thermal performance.
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