Pub Date : 2024-08-27DOI: 10.1016/j.applthermaleng.2024.124247
Fluidized bed reactors have become a pivotal trend in the future development of thermochemical energy storage. However, high temperatures and chemical reactions exacerbate particle attrition in fluidized bed reactors, affecting particle cyclic stability and reducing energy storage efficiency. This study conducted experiments under three different temperature conditions to compare and investigate the attrition mechanisms of CaCO3/CaO particles. The contributions of mechanical forces from collisions, thermal stress due to uneven cooling and heating, and chemical stress from cyclic reactions to particle attrition are analyzed. The edge effects caused by sphericity dominate the attrition behavior during the initial period of fluidization. High-temperature thermal stress significantly weakens the attrition resistance of the particles, while repeated chemical cycling degrades the internal skeletal structure of the particles, lowering the fracture threshold. Based on fitting experimental data, a comprehensive numerical model for predicting particle attrition has been developed and improved by incorporating factors such as edge effects from sphericity, thermally induced stress, and chemically driven fragmentation. Through validation, the model effectively predicts particle attrition behavior in thermochemical storage process, providing a simulation tool for in-depth research on particle stability in thermochemical energy storage field.
{"title":"Integrated attrition model of mechanical-thermal-reaction for CaCO3/CaO thermochemical energy storage","authors":"","doi":"10.1016/j.applthermaleng.2024.124247","DOIUrl":"10.1016/j.applthermaleng.2024.124247","url":null,"abstract":"<div><p>Fluidized bed reactors have become a pivotal trend in the future development of thermochemical energy storage. However, high temperatures and chemical reactions exacerbate particle attrition in fluidized bed reactors, affecting particle cyclic stability and reducing energy storage efficiency. This study conducted experiments under three different temperature conditions to compare and investigate the attrition mechanisms of CaCO<sub>3</sub>/CaO particles. The contributions of mechanical forces from collisions, thermal stress due to uneven cooling and heating, and chemical stress from cyclic reactions to particle attrition are analyzed. The edge effects caused by sphericity dominate the attrition behavior during the initial period of fluidization. High-temperature thermal stress significantly weakens the attrition resistance of the particles, while repeated chemical cycling degrades the internal skeletal structure of the particles, lowering the fracture threshold. Based on fitting experimental data, a comprehensive numerical model for predicting particle attrition has been developed and improved by incorporating factors such as edge effects from sphericity, thermally induced stress, and chemically driven fragmentation. Through validation, the model effectively predicts particle attrition behavior in thermochemical storage process, providing a simulation tool for in-depth research on particle stability in thermochemical energy storage field.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142083338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-08-27DOI: 10.1016/j.applthermaleng.2024.124262
We propose in this study a novel cooling solution for Li-ion battery packs based on Phase Change Materials (PCM) and metallic fins placed around each cell. Discharging and charging processes both melt the PCM. To complete the thermal management of the batteries, an intermediary sequence is added for the PCM solidification. During a short timeframe between batteries charging and discharging, a liquid coolant flows through one small channel located within each fin. A numerical model and a theoretical analysis allow to predict the thermal behavior of the battery cells and the PCM liquid fraction changes in time. It is shown that the combination of a passive cooling solution brought by the PCM with the fast period of liquid cooling for the PCM solidification is an effective solution to control the temperature evolution within the battery cells during discharge and charge. The only external energy consumption foreseen comes from the laminar flow of the coolant for solidification during a very short period of time. The findings indicate that the proposed PCM-liquid cooling integration reduces the total energy consumption by 54.9 % (from 0.4406 kJ to 0.1963 kJ) for the 2C discharging-2C charging cycle compared to traditional liquid-cooling strategy.
{"title":"PCM-based passive cooling solution for Li-ion battery pack, a theoretical and numerical study","authors":"","doi":"10.1016/j.applthermaleng.2024.124262","DOIUrl":"10.1016/j.applthermaleng.2024.124262","url":null,"abstract":"<div><p>We propose in this study a novel cooling solution for Li-ion battery packs based on Phase Change Materials (PCM) and metallic fins placed around each cell. Discharging and charging processes both melt the PCM. To complete the thermal management of the batteries, an intermediary sequence is added for the PCM solidification. During a short timeframe between batteries charging and discharging, a liquid coolant flows through one small channel located within each fin. A numerical model and a theoretical analysis allow to predict the thermal behavior of the battery cells and the PCM liquid fraction changes in time. It is shown that the combination of a passive cooling solution brought by the PCM with the fast period of liquid cooling for the PCM solidification is an effective solution to control the temperature evolution within the battery cells during discharge and charge. The only external energy consumption foreseen comes from the laminar flow of the coolant for solidification during a very short period of time. The findings indicate that the proposed PCM-liquid cooling integration reduces the total energy consumption by 54.9 % (from 0.4406 kJ to 0.1963 kJ) for the 2C discharging-2C charging cycle compared to traditional liquid-cooling strategy.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142099444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-08-27DOI: 10.1016/j.applthermaleng.2024.124263
Due to the pressing need for compact layouts, the spacing between high-power devices is gradually decreasing, making the mutual influence between multiple heat sources unavoidable. Therefore, this paper proposes a method based on the adiabatic characteristics of heat flow lines and their convergence positions to evaluate the rationality of the thermal space design of each heat source. This method has been validated for applicability in one-dimensional, two-dimensional, and three-dimensional multi-heat-source conjugate convection heat transfer. Heat flow lines have significant advantages in describing energy flow, as they align with the direction of the temperature gradient. In thermal spaces with adiabatic boundaries or mutual influences between multiple heat sources, heat flow lines converge at certain positions. The relationship between adiabatic boundaries and heat flow line convergence positions has been studied, and a more interpretative decoupling scheme for multi-heat-source systems has been proposed. The main feature of this scheme is the separation of each heat source in the same steady-state thermal space and assigning adiabatic boundaries to the solid partition surfaces, allowing efficient observation of the thermal conditions of individual heat sources and targeted layout optimization. Results indicate that this method can utilize changes in heat flow line convergence positions to assess current thermal conditions and can be used to compare the thermal performance of different shaped heat sinks. Simulation results show that under the same mass conditions, thin-fin heat sinks perform 47 % better than thick-fin heat sinks, providing a more comprehensive and intuitive assessment compared to metrics such as thermal resistance and average temperature. The proposed method offers new ideas for multi-heat-source layout optimization, heat flow control, multi-heat-source partitioned simulation, and abnormal heating detection in multiple heat sources.
{"title":"Research on the division of heat dissipation spaces for multiple heat sources based on the adiabatic characteristic of heat flow lines","authors":"","doi":"10.1016/j.applthermaleng.2024.124263","DOIUrl":"10.1016/j.applthermaleng.2024.124263","url":null,"abstract":"<div><p>Due to the pressing need for compact layouts, the spacing between high-power devices is gradually decreasing, making the mutual influence between multiple heat sources unavoidable. Therefore, this paper proposes a method based on the adiabatic characteristics of heat flow lines and their convergence positions to evaluate the rationality of the thermal space design of each heat source. This method has been validated for applicability in one-dimensional, two-dimensional, and three-dimensional multi-heat-source conjugate convection heat transfer. Heat flow lines have significant advantages in describing energy flow, as they align with the direction of the temperature gradient. In thermal spaces with adiabatic boundaries or mutual influences between multiple heat sources, heat flow lines converge at certain positions. The relationship between adiabatic boundaries and heat flow line convergence positions has been studied, and a more interpretative decoupling scheme for multi-heat-source systems has been proposed. The main feature of this scheme is the separation of each heat source in the same steady-state thermal space and assigning adiabatic boundaries to the solid partition surfaces, allowing efficient observation of the thermal conditions of individual heat sources and targeted layout optimization. Results indicate that this method can utilize changes in heat flow line convergence positions to assess current thermal conditions and can be used to compare the thermal performance of different shaped heat sinks. Simulation results show that under the same mass conditions, thin-fin heat sinks perform 47 % better than thick-fin heat sinks, providing a more comprehensive and intuitive assessment compared to metrics such as thermal resistance and average temperature. The proposed method offers new ideas for multi-heat-source layout optimization, heat flow control, multi-heat-source partitioned simulation, and abnormal heating detection in multiple heat sources.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142150884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-08-26DOI: 10.1016/j.applthermaleng.2024.124261
Based on the photovoltaic (PV) system, phase change materials (PCMs), thermoelectric generators (TEGs), and cooling water are combined to form a photovoltaic thermal application (PV-PCM/TEG-T) system. The system is also compared with the PV and photovoltaic phase change thermal (PV-PCM-T) systems for environmental and economic analyses. The environmental analyses shows that the environmental impacts of the three systems are mainly concentrated in the production phase, with the aluminum frames and PV panels being the primary sources of the environmental effects, while the addition of paraffin wax and TEG have relatively minor environmental impacts. Economic analyses shows that the system generates electricity for 0.076 $/kW h, with the purchase of TEGs being the main capital expenditure. At the same time, the energy payback time of this system is 17.5 % shorter than that of the PV system and 6.9 % shorter than that of the PV-PCM-T system. The life cycle conversion efficiency is 55 % higher than that of the PV system and 23.9 % higher than that of the PV-PCM-T system, which provides better energy saving. In addition, with the continuous development of TEG manufacturing technology, the PV-PCM-TEG-T system will have better economic benefits and application potential.
{"title":"Economic and life cycle analysis of a photovoltaic thermal application system based on phase change thermal storage","authors":"","doi":"10.1016/j.applthermaleng.2024.124261","DOIUrl":"10.1016/j.applthermaleng.2024.124261","url":null,"abstract":"<div><p>Based on the photovoltaic (PV) system, phase change materials (PCMs), thermoelectric generators (TEGs), and cooling water are combined to form a photovoltaic thermal application (PV-PCM/TEG-T) system. The system is also compared with the PV and photovoltaic phase change thermal (PV-PCM-T) systems for environmental and economic analyses. The environmental analyses shows that the environmental impacts of the three systems are mainly concentrated in the production phase, with the aluminum frames and PV panels being the primary sources of the environmental effects, while the addition of paraffin wax and TEG have relatively minor environmental impacts. Economic analyses shows that the system generates electricity for 0.076 $/kW h, with the purchase of TEGs being the main capital expenditure. At the same time, the energy payback time of this system is 17.5 % shorter than that of the PV system and 6.9 % shorter than that of the PV-PCM-T system. The life cycle conversion efficiency is 55 % higher than that of the PV system and 23.9 % higher than that of the PV-PCM-T system, which provides better energy saving. In addition, with the continuous development of TEG manufacturing technology, the PV-PCM-TEG-T system will have better economic benefits and application potential.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142099442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-08-26DOI: 10.1016/j.applthermaleng.2024.124238
Twin-screw compressors (TSC) are commonly used in heat pump processes due to their robustness and flexibility. They exhibit two core properties, i.e. the swept volume and the built-in volume ratio (BVR), which heavily influence their capacity limits and off-design efficiency. This work presents a new low-order model (i.e. a polynomial model), which can accurately predict a TSC’s behaviour. The model uses the external pressure ratio and volumetric compressor inlet flow rate to calculate isentropic efficiency and compressor speed. The input parameters are normalised with a reference flow rate (calculated from the swept volume) and the BVR, respectively. This results in a generalised model of low numerical cost, which can be used for explorative studies independent of the specific machine size and BVR. A gain in computational speed by a factor of 375 is achieved compared to a semi-empiric reference model. The model displays very good predictive accuracy when used to predict the performance of machines with similar BVRs, but different sizes. A mean deviation from the manufacturer data of 4.29 , 0.88 and 1.38 for the shaft power, the outlet temperature and the compressor speed can be observed, respectively. When there is a difference in size and BVR, the prediction accuracy is still reasonable but significantly declines for small and very large pressure ratios. Nevertheless, the proposed new approach extends the state-of-the-art by introducing a low-order model, which combines the advantages of low computational cost, high accuracy, physically correct predictions over a wide operational range and scalability to different machine capacities and BVRs. The validation for different fluids indicates a good general prediction accuracy relatively independent of the used fluid.
{"title":"Fast and accurate modelling of twin-screw compressors: A generalised low-order approach","authors":"","doi":"10.1016/j.applthermaleng.2024.124238","DOIUrl":"10.1016/j.applthermaleng.2024.124238","url":null,"abstract":"<div><p>Twin-screw compressors (TSC) are commonly used in heat pump processes due to their robustness and flexibility. They exhibit two core properties, i.e. the swept volume and the built-in volume ratio (BVR), which heavily influence their capacity limits and off-design efficiency. This work presents a new low-order model (i.e. a polynomial model), which can accurately predict a TSC’s behaviour. The model uses the external pressure ratio and volumetric compressor inlet flow rate to calculate isentropic efficiency and compressor speed. The input parameters are normalised with a reference flow rate (calculated from the swept volume) and the BVR, respectively. This results in a generalised model of low numerical cost, which can be used for explorative studies independent of the specific machine size and BVR. A gain in computational speed by a factor of 375 is achieved compared to a semi-empiric reference model. The model displays very good predictive accuracy when used to predict the performance of machines with similar BVRs, but different sizes. A mean deviation from the manufacturer data of 4.29<!--> <span><math><mtext>%</mtext></math></span>, 0.88<!--> <span><math><mrow><msup><mrow></mrow><mrow><mo>°</mo></mrow></msup><mtext>C</mtext></mrow></math></span> and 1.38<!--> <span><math><mtext>%</mtext></math></span> for the shaft power, the outlet temperature and the compressor speed can be observed, respectively. When there is a difference in size and BVR, the prediction accuracy is still reasonable but significantly declines for small and very large pressure ratios. Nevertheless, the proposed new approach extends the state-of-the-art by introducing a low-order model, which combines the advantages of low computational cost, high accuracy, physically correct predictions over a wide operational range and scalability to different machine capacities and BVRs. The validation for different fluids indicates a good general prediction accuracy relatively independent of the used fluid.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S1359431124019069/pdfft?md5=ccdb1075ede3e35b3160d3deb1cead29&pid=1-s2.0-S1359431124019069-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142083341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-26DOI: 10.1016/j.applthermaleng.2024.124242
The building sector has an important impact on the environment, being responsible for 30 % of the total greenhouse gas emissions. Knowing that the energy consumption devoted to HVAC systems accounts for 50 % of the total energy consumption of buildings, it is paramount to develop environmentally friendly technologies able to provide green space heating to the building sector. To that purpose, this manuscript presents a computational study on propane vapor compression heat pumps which include thermoelectric subcooling to boost their operation. The combination of these technologies has been proven in the past to be very beneficial for refrigeration systems and this study concludes for the first time that propane heat pumps can highly benefit from thermoelectric subcooling. The widely conducted research includes the following parameters: ambient temperatures from −20 to 15 °C, voltage supplies to the thermoelectric modules from 0.5 to 10 VDC, number of thermoelectric subcooling blocks from 1 to 8 and two water inlet temperatures, 40 and 55 °C to study their influence on heating capacity, compressor and thermoelectric power consumptions, subcooling degree, propane mass flow, compressor capacity, COP, energy consumption and SCOP of the combined heat pump. The obtained results are very conclusive, COP enhancements up to 12.29 % are achieved when a thermoelectric subcooler with 16 modules is included in a propane heat pump already provided with an internal heat exchanger for an ambient temperature of −20 °C and a water inlet temperature of 55 °C. Additionally, improvements in Seasonal COP up to 9.98 % are achieved if the above-mentioned technologies integration between a vapor compression heat pump and a thermoelectric subcooler substitutes a conventional propane heat pump with an internal heat exchanger for space heating a single-story two-family house.
建筑行业对环境有着重要影响,其温室气体排放量占总排放量的 30%。暖通空调系统的能耗占建筑物总能耗的 50%,因此,开发能够为建筑行业提供绿色空间供热的环保技术至关重要。为此,本手稿介绍了一项关于丙烷蒸汽压缩热泵的计算研究,其中包括热电过冷技术,以促进热泵的运行。这些技术的结合在过去已被证明对制冷系统非常有益,而本研究首次得出结论,丙烷热泵可以从热电过冷中获得巨大收益。广泛开展的研究包括以下参数:-20 至 15 °C 的环境温度、0.5 至 10 VDC 的热电模块供电电压、1 至 8 个热电过冷块的数量以及 40 和 55 °C 两种进水温度,以研究它们对组合热泵的加热能力、压缩机和热电功耗、过冷度、丙烷质量流量、压缩机容量、COP、能耗和 SCOP 的影响。所得结果非常有说服力,在环境温度为 -20 °C 和进水温度为 55 °C 的丙烷热泵中加入 16 个模块的热电过冷却器后,COP 可提高 12.29%。此外,如果将蒸汽压缩热泵和热电过冷却器之间的上述技术整合在一起,取代传统的带内部热交换器的丙烷热泵,用于单层两户住宅的空间供暖,则季节性 COP 可提高到 9.98%。
{"title":"Effect of thermoelectric subcooling on COP and energy consumption of a propane heat pump","authors":"","doi":"10.1016/j.applthermaleng.2024.124242","DOIUrl":"10.1016/j.applthermaleng.2024.124242","url":null,"abstract":"<div><p>The building sector has an important impact on the environment, being responsible for 30 % of the total greenhouse gas emissions. Knowing that the energy consumption devoted to HVAC systems accounts for 50 % of the total energy consumption of buildings, it is paramount to develop environmentally friendly technologies able to provide green space heating to the building sector. To that purpose, this manuscript presents a computational study on propane vapor compression heat pumps which include thermoelectric subcooling to boost their operation. The combination of these technologies has been proven in the past to be very beneficial for refrigeration systems and this study concludes for the first time that propane heat pumps can highly benefit from thermoelectric subcooling. The widely conducted research includes the following parameters: ambient temperatures from −20 to 15 °C, voltage supplies to the thermoelectric modules from 0.5 to 10 VDC, number of thermoelectric subcooling blocks from 1 to 8 and two water inlet temperatures, 40 and 55 °C to study their influence on heating capacity, compressor and thermoelectric power consumptions, subcooling degree, propane mass flow, compressor capacity, COP, energy consumption and SCOP of the combined heat pump. The obtained results are very conclusive, COP enhancements up to 12.29 % are achieved when a thermoelectric subcooler with 16 modules is included in a propane heat pump already provided with an internal heat exchanger for an ambient temperature of −20 °C and a water inlet temperature of 55 °C. Additionally, improvements in Seasonal COP up to 9.98 % are achieved if the above-mentioned technologies integration between a vapor compression heat pump and a thermoelectric subcooler substitutes a conventional propane heat pump with an internal heat exchanger for space heating a single-story two-family house.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S1359431124019100/pdfft?md5=078cff324d15b103b80fd6a5c78817aa&pid=1-s2.0-S1359431124019100-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142099743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-26DOI: 10.1016/j.applthermaleng.2024.124250
Closed cycle power generation systems offer a possible solution to meet the high electricity needs of hypersonic vehicles, but the power generation is limited by the finite cold source and cycle temperature. Introducing two-phase flow liquid metal (LM) MHD power generation based on Closed-Brayton-Cycle (CBC) is a potential solution that can enhance the thermal-electricity conversion process at the system level. However, it is difficult to reflect the complex coupling relationship between the power generation system and the vehicles propulsion system and the limitations of finite cold sources by relying only on ideal system analysis, especially the contradiction between the void fraction and the mass flow of working fluid after the introduction of LMMHD power generation. The study utilizes a multi-dimensional model to evaluate the performance of the CBC enhanced by multi-stage LMMHD generators coupled with hydrocarbon fuel scramjet. The multi-stage mixing-separation LMMHD generator is proposed to decouple the void fraction of the MHD channel and the wall cooling process, and control the void fraction by change number of stages. The calculation result indicate that the void fraction significantly affects the overall power generation performance, including output power, performance boundary, etc. Increasing the void fraction is beneficial, and the optimal void fraction is 0.65. At the same Mach number, the fuel cooling capacity available to the system increases with the fuel equivalence ratio, resulting in higher total power output. The maximum Mach number for thermal protection of the combustor walls alone may surpass 9.5. For gas void fractions of 0.35/0.5/0.65, the maximum power generation reaches 182.8/167.1/156.9 kW, respectively. The novel system is compared with other advanced thermal-electricity conversion cycles under nearly the same conditions and demonstrated clear performance advantages.
{"title":"Coupling study of onboard power generation system of Magnetohydrodynamics enhanced Brayton Cycle","authors":"","doi":"10.1016/j.applthermaleng.2024.124250","DOIUrl":"10.1016/j.applthermaleng.2024.124250","url":null,"abstract":"<div><p>Closed cycle power generation systems offer a possible solution to meet the high electricity needs of hypersonic vehicles, but the power generation is limited by the finite cold source and cycle temperature. Introducing two-phase flow liquid metal (LM) MHD power generation based on Closed-Brayton-Cycle (CBC) is a potential solution that can enhance the thermal-electricity conversion process at the system level. However, it is difficult to reflect the complex coupling relationship between the power generation system and the vehicles propulsion system and the limitations of finite cold sources by relying only on ideal system analysis, especially the contradiction between the void fraction and the mass flow of working fluid after the introduction of LMMHD power generation. The study utilizes a multi-dimensional model to evaluate the performance of the CBC enhanced by multi-stage LMMHD generators coupled with hydrocarbon fuel scramjet. The multi-stage mixing-separation LMMHD generator is proposed to decouple the void fraction of the MHD channel and the wall cooling process, and control the void fraction by change number of stages. The calculation result indicate that the void fraction significantly affects the overall power generation performance, including output power, performance boundary, etc. Increasing the void fraction is beneficial, and the optimal void fraction is 0.65. At the same Mach number, the fuel cooling capacity available to the system increases with the fuel equivalence ratio, resulting in higher total power output. The maximum Mach number for thermal protection of the combustor walls alone may surpass 9.5. For gas void fractions of 0.35/0.5/0.65, the maximum power generation reaches 182.8/167.1/156.9 kW, respectively. The novel system is compared with other advanced thermal-electricity conversion cycles under nearly the same conditions and demonstrated clear performance advantages.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142099576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-08-25DOI: 10.1016/j.applthermaleng.2024.124236
This study aimed at development of a pressure drop prediction method at a drying process by flowing air through a wet particle packed bed saturated with distilled water. At first, the pressure drop measurement during the drying process of the wet particle packed bead of glass sphere was carried out, and a method for predicting the pressure difference of the bed was proposed by investigating the effect of liquid saturation on the bed void fraction. It was clarified that the effect could be predicted by a simple model by considering liquid bridges formed between particles. Next, the liquid saturation when the measured pressure difference suddenly decreased was investigated as the residual saturation. The value was like that of past research. Finally, considering the effect of liquid saturation on the bed void fraction and the influence of the residual saturation on the relative permeability of liquid phase, more than 90 % of all pressure drop data could be predicted with an error of less than ±15 %. Furthermore, in the range where the gas-phase velocity was large, it was important to predict the pressure difference considering the change of the bed void fraction and the residual saturation.
{"title":"Measurement and prediction of void fraction and pressure drop during air drying process of wet particle packed bed","authors":"","doi":"10.1016/j.applthermaleng.2024.124236","DOIUrl":"10.1016/j.applthermaleng.2024.124236","url":null,"abstract":"<div><p>This study aimed at development of a pressure drop prediction method at a drying process by flowing air through a wet particle packed bed saturated with distilled water. At first, the pressure drop measurement during the drying process of the wet particle packed bead of glass sphere was carried out, and a method for predicting the pressure difference of the bed was proposed by investigating the effect of liquid saturation on the bed void fraction. It was clarified that the effect could be predicted by a simple model by considering liquid bridges formed between particles. Next, the liquid saturation when the measured pressure difference suddenly decreased was investigated as the residual saturation. The value was like that of past research. Finally, considering the effect of liquid saturation on the bed void fraction and the influence of the residual saturation on the relative permeability of liquid phase, more than 90 % of all pressure drop data could be predicted with an error of less than ±15 %. Furthermore, in the range where the gas-phase velocity was large, it was important to predict the pressure difference considering the change of the bed void fraction and the residual saturation.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S1359431124019045/pdfft?md5=e363d4adafd8a8d60917d93e75f46523&pid=1-s2.0-S1359431124019045-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142099742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-25DOI: 10.1016/j.applthermaleng.2024.124255
Supercritical carbon dioxide (sCO2) and ammonia (NH3) can be used as coolants in high power-density microelectronics. sCO2 at the micro scale provides enhanced heat transfer solutions for a range of microelectronics cooling applications·NH3 can also potentially provide appropriate cooling solutions as it has favorable thermophysical properties at high pressure, and it can be used as an energy carrier as it contains Hydrogen atoms. Near its critical and pseudocritical condition sCO2 exhibits abrupt changes in its thermophysical properties and at similar pressures liquid NH3 too has adequate properties that make it a good coolant. While sCO2 is non-toxic, NH3 is a toxic substance and should only be used in closed loop micro heat exchangers.
The current study compares the convective heat transfer performance of supercritical carbon dioxide (sCO2) and ammonia for microchannel cooling. A total of 144 numerical cases inside a square microchannel of hydraulic diameter of 200 µm with a total length of 52 mm and a heated length of 50 mm at constant surface temperatures in laminar flow conditions were examined. Two scenarios were investigated, in one the inlet mass flux was kept constant at 100, 150, and 200 kg/m2s, and in the second the pressure drop across the microchannel was maintained at 200, 400, and 600 Pa. Both scenarios were investigated at pressures of 8 and 10 MPa and at surface temperatures of 32, 40, 50, 60, 70, and 80 °C. In all cases the inlet temperature of both fluids was kept at 21 °C. At the same mass flux, NH3 yielded a higher average heat transfer coefficient (havg) but at the same pressure drop, sCO2 resulted in higher havg at certain surface temperatures. The havg for NH3 didn’t show significant variation but for sCO2 it showed significant change with surface temperature, and this was due to the significant change in the thermophysical properties of sCO2. The havg showed a mixed behavior with respect to the pumping power. The coefficient of performance (COP) was as high as 600,000 for sCO2 and it was significantly higher than that for NH3. Near the pseudocritical region, the COP for sCO2 witnessed a significant improvement, more than double, for 8 MPa compared to 10 MPa.
{"title":"A comparative analysis of ammonia and supercritical carbon dioxide in horizontal microchannels","authors":"","doi":"10.1016/j.applthermaleng.2024.124255","DOIUrl":"10.1016/j.applthermaleng.2024.124255","url":null,"abstract":"<div><p>Supercritical carbon dioxide (<em>sCO<sub>2</sub></em>) and ammonia (<em>NH<sub>3</sub></em>) can be used as coolants in high power-density microelectronics. <em>sCO<sub>2</sub></em> at the micro scale provides enhanced heat transfer solutions for a range of microelectronics cooling applications·<em>NH<sub>3</sub></em> can also potentially provide appropriate cooling solutions as it has favorable thermophysical properties at high pressure, and it can be used as an energy carrier as it contains Hydrogen atoms. Near its critical and pseudocritical condition <em>sCO<sub>2</sub></em> exhibits abrupt changes in its thermophysical properties and at similar pressures liquid <em>NH<sub>3</sub></em> too has adequate properties that make it a good coolant. While <em>sCO<sub>2</sub></em> is non-toxic, <em>NH<sub>3</sub></em> is a toxic substance and should only be used in closed loop micro heat exchangers.</p><p>The current study compares the convective heat transfer performance of supercritical carbon dioxide (<em>sCO<sub>2</sub></em>) and ammonia for microchannel cooling. A total of 144 numerical cases inside a square microchannel of hydraulic diameter of 200 µm with a total length of 52 mm and a heated length of 50 mm at constant surface temperatures in laminar flow conditions were examined. Two scenarios were investigated, in one the inlet mass flux was kept constant at 100, 150, and 200 kg/m<sup>2</sup>s, and in the second the pressure drop across the microchannel was maintained at 200, 400, and 600 Pa. Both scenarios were investigated at pressures of 8 and 10 MPa and at surface temperatures of 32, 40, 50, 60, 70, and 80 °C. In all cases the inlet temperature of both fluids was kept at 21 °C. At the same mass flux, <em>NH<sub>3</sub></em> yielded a higher average heat transfer coefficient (<em>h<sub>avg</sub></em>) but at the same pressure drop, <em>sCO<sub>2</sub></em> resulted in higher <em>h<sub>avg</sub></em> at certain surface temperatures. The <em>h<sub>avg</sub></em> for <em>NH<sub>3</sub></em> didn’t show significant variation but for <em>sCO<sub>2</sub></em> it showed significant change with surface temperature, and this was due to the significant change in the thermophysical properties of <em>sCO<sub>2</sub></em>. The <em>h<sub>avg</sub></em> showed a mixed behavior with respect to the pumping power. The coefficient of performance (<em>COP</em>) was as high as 600,000 for <em>sCO<sub>2</sub></em> and it was significantly higher than that for <em>NH<sub>3</sub></em>. Near the pseudocritical region, the <em>COP</em> for <em>sCO<sub>2</sub></em> witnessed a significant improvement, more than double, for 8 MPa compared to 10 MPa.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142121702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-08-25DOI: 10.1016/j.applthermaleng.2024.124257
The introduction of phase change materials (PCMs) into battery thermal management systems (BTMS) can effectively enhance the cooling performance, safety and practical thermal management applications of lithium-ion batteries (LIBs). However, further study is needed to address the low heat conductivity and rapid phase change leakage of PCMs. This study proposed a metal–organic framework based shape-stabilized composite PCM (MOF/expanded graphite (EG) /multi-walled carbon nanotube (MWCNT) /paraffin wax (PW)) to construe battery cooling system, and its effect of battery thermal management is experimentally tested under various conditions. The results show the CPCM reveals a superior thermal management effect under varying ambient temperatures and discharge multipliers and outperforms natural convection. Even in the harsh environment of 40 °C and 3 C, the maximum temperature (Tmax) and Tmax difference (ΔTmax) of the CPCM-cooled module are 61.38 and 2.67 °C, which are 22 and 9 °C below the natural air-cooled module. Remarkably, the ΔTmax of the CPCM-cooled battery module in discharge decreases with the temperature rise at the discharge rate of 3 C, which is the exact opposite to the case of the air-cooled module. Moreover, the ΔTmax of CPCM-cooled module is 1.69, 1.84, 2.67 °C, all below the safe 5 °C at high temperatures (40 °C) as the discharge rate increases. The designed MOF-CPCM cooling system can effectively improve the temperature uniformity and thermal safety of the battery in harsh environments. Therefore, this novel MOF-based CPCM shows great promise in BTM.
{"title":"Enhancement of battery thermal management effect by a novel MOF based composite phase change material","authors":"","doi":"10.1016/j.applthermaleng.2024.124257","DOIUrl":"10.1016/j.applthermaleng.2024.124257","url":null,"abstract":"<div><p>The introduction of phase change materials (PCMs) into battery thermal management systems (BTMS) can effectively enhance the cooling performance, safety and practical thermal management applications of lithium-ion batteries (LIBs). However, further study is needed to address the low heat conductivity and rapid phase change leakage of PCMs. This study proposed a metal–organic framework based shape-stabilized composite PCM (MOF/expanded graphite (EG) /multi-walled carbon nanotube (MWCNT) /paraffin wax (PW)) to construe battery cooling system, and its effect of battery thermal management is experimentally tested under various conditions. The results show the CPCM reveals a superior thermal management effect under varying ambient temperatures and discharge multipliers and outperforms natural convection. Even in the harsh environment of 40 °C and 3 C, the maximum temperature (T<sub>max</sub>) and T<sub>max</sub> difference (ΔT<sub>max</sub>) of the CPCM-cooled module are 61.38 and 2.67 °C, which are 22 and 9 °C below the natural air-cooled module. Remarkably, the ΔT<sub>max</sub> of the CPCM-cooled battery module in discharge decreases with the temperature rise at the discharge rate of 3 C, which is the exact opposite to the case of the air-cooled module. Moreover, the ΔT<sub>max</sub> of CPCM-cooled module is 1.69, 1.84, 2.67 °C, all below the safe 5 °C at high temperatures (40 °C) as the discharge rate increases. The designed MOF-CPCM cooling system can effectively improve the temperature uniformity and thermal safety of the battery in harsh environments. Therefore, this novel MOF-based CPCM shows great promise in BTM.</p></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":null,"pages":null},"PeriodicalIF":6.1,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142076232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}