Pub Date : 2022-07-12DOI: 10.3389/fther.2022.931069
Peimiao Li, Hui Wang, Min Chang, J. Bai
Aiming to study the electrical characteristics of photovoltaic cells during the flight of solar-powered unmanned aerial vehicles, this work combines a photovoltaic cell equivalent circuit model and a thermodynamic model. The influence of wing surface temperature and its influencing factor-solar radiation is of primary concern. A solar radiation model is established to explore the impact of solar irradiance on temperature and photovoltaic cell output. Atmospheric temperature and four basic parameters of photovoltaic cell, including open-circuit voltage, short-circuit current, voltage, and current at maximum power point under standard conditions are treated as input parameters. The surface temperature, the variation of output voltage, current, and power are studied with the altitude changing from 0 to 35 km and time from 0 to 24 h in spring equinoxes. Results find that with the increase in altitude, the surface temperature of the photovoltaic cell decreases first and then increases. The voltage of the photovoltaic cell decreases as the temperature increases, and the voltage-time curve varies at altitudes below 25 km and above 30 km. The peak power is available at an altitude between 15 and 20 km. The above findings can be applied to study energy generations and flows of solar-powered vehicles.
{"title":"Electrical Characteristics of Photovoltaic Cell in Solar-Powered Aircraft During Cruise","authors":"Peimiao Li, Hui Wang, Min Chang, J. Bai","doi":"10.3389/fther.2022.931069","DOIUrl":"https://doi.org/10.3389/fther.2022.931069","url":null,"abstract":"Aiming to study the electrical characteristics of photovoltaic cells during the flight of solar-powered unmanned aerial vehicles, this work combines a photovoltaic cell equivalent circuit model and a thermodynamic model. The influence of wing surface temperature and its influencing factor-solar radiation is of primary concern. A solar radiation model is established to explore the impact of solar irradiance on temperature and photovoltaic cell output. Atmospheric temperature and four basic parameters of photovoltaic cell, including open-circuit voltage, short-circuit current, voltage, and current at maximum power point under standard conditions are treated as input parameters. The surface temperature, the variation of output voltage, current, and power are studied with the altitude changing from 0 to 35 km and time from 0 to 24 h in spring equinoxes. Results find that with the increase in altitude, the surface temperature of the photovoltaic cell decreases first and then increases. The voltage of the photovoltaic cell decreases as the temperature increases, and the voltage-time curve varies at altitudes below 25 km and above 30 km. The peak power is available at an altitude between 15 and 20 km. The above findings can be applied to study energy generations and flows of solar-powered vehicles.","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42350637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-07-06DOI: 10.3389/fther.2022.940072
Zhibin Yu
Heat accounts for almost half of global final energy consumption (IEA, 2021a). Industrial processes are responsible for 51% of the energy consumed for heat, while another 46% is consumed for space and water heating. Heat supply currently relies heavily on fossil fuels, contributing more than 40% of global energy related CO2 emissions in 2020 (IEA, 2021a). Renewable sources only met less than a quarter of global heat demand in 2020 (IEA, 2021b). In order to achieve the target of net zero of greenhouse gas emissions by 2050, heat must be decarbonised; this presents a grand challenge to academia, industry, and society.
{"title":"Grand Challenges in Heat Decarbonisation","authors":"Zhibin Yu","doi":"10.3389/fther.2022.940072","DOIUrl":"https://doi.org/10.3389/fther.2022.940072","url":null,"abstract":"Heat accounts for almost half of global final energy consumption (IEA, 2021a). Industrial processes are responsible for 51% of the energy consumed for heat, while another 46% is consumed for space and water heating. Heat supply currently relies heavily on fossil fuels, contributing more than 40% of global energy related CO2 emissions in 2020 (IEA, 2021a). Renewable sources only met less than a quarter of global heat demand in 2020 (IEA, 2021b). In order to achieve the target of net zero of greenhouse gas emissions by 2050, heat must be decarbonised; this presents a grand challenge to academia, industry, and society.","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44509654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-29DOI: 10.3389/fther.2022.905015
Ke Du, Huijun Wu, Yanling Guo, G. Huang, Xin-hua Xu, Yanchen Liu
Radiant cooling has well been acknowledged as energy efficient and thermal comfortable technology compared to conventional convective cooling. However, the radiant cooling exists two serious problems (viz., insufficient cooling capacity and high condensation risk) especially in hot and humid climate zones. By adding double-skin infrared transparent membranes (DIMs) onto radiant cooling panel, the air-contact surface can be separated from the cooling source surface, which makes it possible to use a low-temperature cooling source while maintaining air-contact surface higher than dew point temperature. The DIMs are transparent to radiant heat transfer which yields great cooling capacity while chilled ceiling has high emissivity (e.g., above 0.9). However, for metal chilled ceilings having low emissivity, radiant heat from cooling load to chilled ceiling would be reduced through DIMs, which results in insufficient cooling capacity. In this paper, a type of adaptive double-skin infrared membranes (a-DIMs) consisting a high-emissivity membrane and a high transparent membrane is proposed to improve cooling capacity of conventional metal chilled ceilings. The high-emissivity membrane serves as radiant cooling surface instead of low-emissivity chilled ceiling so as to improve radiant heat flux, while the high transparent membrane permits great radiant heat from cooling load to chilled ceiling. A combined heat transfer analysis based on semi-transparent surface radiation and natural convection were carried out to predict cooling capacity of condensation-free radiant cooling. The results indicate that the cooling capacity could be up to 101.9W/㎡ by adding a-DIMs consisting of a high-emissivity membrane of 0.96 and a high transparent membrane of 0.87, which is improved by 2 times compared to conventional metal chilled ceiling with low emissivity of 0.2. Moreover, the cooling capacity by adding a-DIMs is further improved by 25% compared to that by using both infrared transparent DIMs presented in our previous work. The results also indicate that the cooling capacity could be improved by above 2 times compared to conventional low-emissivity metal chilled ceiling by using the radiant cooling with a-DIMs for various humidity. It will be of great guidance for high-performance radiant cooling design without condensation and improved cooling capacity for low-emissivity metal chilled ceiling.
{"title":"Improving Cooling Capacity of Condensation-Free Radiant Cooling for Low-Emissivity Chilled Ceiling via Adaptive Double-Skin Infrared Membranes","authors":"Ke Du, Huijun Wu, Yanling Guo, G. Huang, Xin-hua Xu, Yanchen Liu","doi":"10.3389/fther.2022.905015","DOIUrl":"https://doi.org/10.3389/fther.2022.905015","url":null,"abstract":"Radiant cooling has well been acknowledged as energy efficient and thermal comfortable technology compared to conventional convective cooling. However, the radiant cooling exists two serious problems (viz., insufficient cooling capacity and high condensation risk) especially in hot and humid climate zones. By adding double-skin infrared transparent membranes (DIMs) onto radiant cooling panel, the air-contact surface can be separated from the cooling source surface, which makes it possible to use a low-temperature cooling source while maintaining air-contact surface higher than dew point temperature. The DIMs are transparent to radiant heat transfer which yields great cooling capacity while chilled ceiling has high emissivity (e.g., above 0.9). However, for metal chilled ceilings having low emissivity, radiant heat from cooling load to chilled ceiling would be reduced through DIMs, which results in insufficient cooling capacity. In this paper, a type of adaptive double-skin infrared membranes (a-DIMs) consisting a high-emissivity membrane and a high transparent membrane is proposed to improve cooling capacity of conventional metal chilled ceilings. The high-emissivity membrane serves as radiant cooling surface instead of low-emissivity chilled ceiling so as to improve radiant heat flux, while the high transparent membrane permits great radiant heat from cooling load to chilled ceiling. A combined heat transfer analysis based on semi-transparent surface radiation and natural convection were carried out to predict cooling capacity of condensation-free radiant cooling. The results indicate that the cooling capacity could be up to 101.9W/㎡ by adding a-DIMs consisting of a high-emissivity membrane of 0.96 and a high transparent membrane of 0.87, which is improved by 2 times compared to conventional metal chilled ceiling with low emissivity of 0.2. Moreover, the cooling capacity by adding a-DIMs is further improved by 25% compared to that by using both infrared transparent DIMs presented in our previous work. The results also indicate that the cooling capacity could be improved by above 2 times compared to conventional low-emissivity metal chilled ceiling by using the radiant cooling with a-DIMs for various humidity. It will be of great guidance for high-performance radiant cooling design without condensation and improved cooling capacity for low-emissivity metal chilled ceiling.","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42214361","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-23DOI: 10.3389/fther.2022.886322
Huan Wang, Hongli Yan, J. Ren, B. Li, S. Nyallang Nyamsi, Zhen Wu
Graphical Abstract Hydrogen, as a kind of green and efficient energy, plays an increasingly important role in current social development. Hydrogen storage technology is considered to be one of the main bottlenecks in limiting the large-scale application of hydrogen energy. The solid-state hydrogen storage technology based on Mg-based materials has received extensive attention due to its advantages of high hydrogen capacity, good reversibility, and low cost, but there are still shortcomings such as high reaction temperature, large energy consumption, and slow reaction kinetics. In order to solve these problems, this article proposes a new method of using microwave plasma to ionize hydrogen into H− ion. The possible activation mechanism of microwave plasma to improve the hydrogen storage properties is put forward. Based on the activation mechanism, the thermodynamic performance of Mg-based hydrogen storage is evaluated using density functional theory. It is concluded that the reaction temperature is significantly reduced from 339°C to 109°C with the help of microwave plasma. In addition, the comparison between the conventional heating hydrogen storage process based on MgH2 and microwave enhanced advanced hydrogen storage process based on MgH2 systems coupled with solid oxide fuel cells for heat and power generation is conducted to evaluate the economic feasibility. The results show that the energy consumption cost of the proposed microwave plasma enhancing hydrogen storage system is approximately 1.71 $/kgH2, which is about 50% of the energy consumption cost of the conventional system.
{"title":"Microwave Plasma Enhancing Mg-Based Hydrogen Storage: Thermodynamics Evaluation and Economic Analysis of Coupling SOFC for Heat and Power Generation","authors":"Huan Wang, Hongli Yan, J. Ren, B. Li, S. Nyallang Nyamsi, Zhen Wu","doi":"10.3389/fther.2022.886322","DOIUrl":"https://doi.org/10.3389/fther.2022.886322","url":null,"abstract":"Graphical Abstract Hydrogen, as a kind of green and efficient energy, plays an increasingly important role in current social development. Hydrogen storage technology is considered to be one of the main bottlenecks in limiting the large-scale application of hydrogen energy. The solid-state hydrogen storage technology based on Mg-based materials has received extensive attention due to its advantages of high hydrogen capacity, good reversibility, and low cost, but there are still shortcomings such as high reaction temperature, large energy consumption, and slow reaction kinetics. In order to solve these problems, this article proposes a new method of using microwave plasma to ionize hydrogen into H− ion. The possible activation mechanism of microwave plasma to improve the hydrogen storage properties is put forward. Based on the activation mechanism, the thermodynamic performance of Mg-based hydrogen storage is evaluated using density functional theory. It is concluded that the reaction temperature is significantly reduced from 339°C to 109°C with the help of microwave plasma. In addition, the comparison between the conventional heating hydrogen storage process based on MgH2 and microwave enhanced advanced hydrogen storage process based on MgH2 systems coupled with solid oxide fuel cells for heat and power generation is conducted to evaluate the economic feasibility. The results show that the energy consumption cost of the proposed microwave plasma enhancing hydrogen storage system is approximately 1.71 $/kgH2, which is about 50% of the energy consumption cost of the conventional system.","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47223363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-06-20DOI: 10.3389/fther.2022.945841
Jin-Ku Kim
Thermal Systems has been an integral part of our society as a main way of providing energy for peoples’ day-to-day living as well as industrial activities. Thermal systems are at the heart of energy infrastructure because the generation, distribution, recovery, utilization and storage of energy is related with the transformation, exchange or transfer of thermal heat to another form of energy. Continuous and dedicated efforts from industrial and academic communities have been made to the development of materials, components, equipment, processes and systems for thermal energy technologies, while societal and industrial importance in thermal systems have been fully acknowledged, and its economic benefits have been widely appreciated for generation by generation. Contrary to scientific achievements made for the improvement of thermodynamic efficiency and economics of thermal systems, little attention has been being paid to the sustainable generation and utilization of thermal energy. Recognition of global climate change and its negative impact on society has driven us to turn our focus on the development of net-zero energy technologies and its implementation in our industrial and district thermal systems. The introduction of policies for cutting CO2 emissions and a wide range of pledges for achieving net-zero by 2050 from various countries and companies clearly demonstrate urgency and importance of speeding up the transition of conventional thermal systems to sustainable one. However, it is not straightforward in practice to achieve rapid transition to the carbon-free thermal systems. For the last few centuries, the thermal conversion of fossil fuels has played a main role for generating energy, and industrial and domestic energy systems are equipped with devices and units which are optimized with the utilization of combustion heat from fossil fuels. Clean sources of energy, for example, biomass, renewable, hydrogen, etc have different thermodynamic properties and thermo-physical behaviour, which often requires fundamental changes from materials to system integration of existing fossil-fuel-based technologies. Also, most of net-zero energy technologies are not technologically mature to be readily available for end-users or are not economically viable enough to be competitive to fossil fuel-based technologies. In order to deal with such difficulties and drawbacks related to the introduction of net-zero technologies, various R&D activities should be carried out for achieving the energy-efficient and costeffective use of renewable energy. When new materials are synthesized or equipment is fundamentally upgraded for net-zero thermal systems, technical advances made from such development should be strategically integrated to the existing energy systems or be evolved to propose new paths for the sustainable utilization of thermal energy for the future. On the other hand, scientific efforts for the development of net-zero energy technologies in these days
{"title":"Specialty Grand Challenge for Thermal System Design","authors":"Jin-Ku Kim","doi":"10.3389/fther.2022.945841","DOIUrl":"https://doi.org/10.3389/fther.2022.945841","url":null,"abstract":"Thermal Systems has been an integral part of our society as a main way of providing energy for peoples’ day-to-day living as well as industrial activities. Thermal systems are at the heart of energy infrastructure because the generation, distribution, recovery, utilization and storage of energy is related with the transformation, exchange or transfer of thermal heat to another form of energy. Continuous and dedicated efforts from industrial and academic communities have been made to the development of materials, components, equipment, processes and systems for thermal energy technologies, while societal and industrial importance in thermal systems have been fully acknowledged, and its economic benefits have been widely appreciated for generation by generation. Contrary to scientific achievements made for the improvement of thermodynamic efficiency and economics of thermal systems, little attention has been being paid to the sustainable generation and utilization of thermal energy. Recognition of global climate change and its negative impact on society has driven us to turn our focus on the development of net-zero energy technologies and its implementation in our industrial and district thermal systems. The introduction of policies for cutting CO2 emissions and a wide range of pledges for achieving net-zero by 2050 from various countries and companies clearly demonstrate urgency and importance of speeding up the transition of conventional thermal systems to sustainable one. However, it is not straightforward in practice to achieve rapid transition to the carbon-free thermal systems. For the last few centuries, the thermal conversion of fossil fuels has played a main role for generating energy, and industrial and domestic energy systems are equipped with devices and units which are optimized with the utilization of combustion heat from fossil fuels. Clean sources of energy, for example, biomass, renewable, hydrogen, etc have different thermodynamic properties and thermo-physical behaviour, which often requires fundamental changes from materials to system integration of existing fossil-fuel-based technologies. Also, most of net-zero energy technologies are not technologically mature to be readily available for end-users or are not economically viable enough to be competitive to fossil fuel-based technologies. In order to deal with such difficulties and drawbacks related to the introduction of net-zero technologies, various R&D activities should be carried out for achieving the energy-efficient and costeffective use of renewable energy. When new materials are synthesized or equipment is fundamentally upgraded for net-zero thermal systems, technical advances made from such development should be strategically integrated to the existing energy systems or be evolved to propose new paths for the sustainable utilization of thermal energy for the future. On the other hand, scientific efforts for the development of net-zero energy technologies in these days ","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42701408","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The continuous miniaturization and multi-function of electronic devices have put forward high requirements for the effective removal of the heat generated in the system. Developing thermally conductive polymer composite-based thermal interface materials is becoming the research hotspot. In addition to the usually concerned intrinsic thermal conductivity of the filler itself, surface modification is one of the important ways to form an effective heat conduction pathway and improve the overall thermal conductivity of materials. In this work, we used silicon rubber as the polymer matrix and achieved the thermal conductivity increment via various fillers with different shapes. The adopted fillers are spherical aluminum oxide (Al2O3), linear carbon fiber and boron nitride sheets, which can be considered as zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) fillers respectively. We also prepared the silver-modified fillers and investigated the influence on the formation of heat conduction pathways and interfacial thermal resistance of different shaped fillers. An obvious increment in thermal conductivity of the composite with silver-modified fillers was observed compared to the composite with pristine fillers. Furthermore, through the practical thermal management performance investigation, we found the thermal conductivity increment did improve the actual heat transfer performance of composite elastomers functioning as thermal interface materials
{"title":"Investigation on Silver Modification of Different Shaped Filler on the Heat Conduction Performance Improvement for Silicone Elastomer","authors":"Yifan Li, Yuan Zhang, Yicheng Liu, Huaqing Xie, Wei Yu","doi":"10.3389/fther.2022.935616","DOIUrl":"https://doi.org/10.3389/fther.2022.935616","url":null,"abstract":"The continuous miniaturization and multi-function of electronic devices have put forward high requirements for the effective removal of the heat generated in the system. Developing thermally conductive polymer composite-based thermal interface materials is becoming the research hotspot. In addition to the usually concerned intrinsic thermal conductivity of the filler itself, surface modification is one of the important ways to form an effective heat conduction pathway and improve the overall thermal conductivity of materials. In this work, we used silicon rubber as the polymer matrix and achieved the thermal conductivity increment via various fillers with different shapes. The adopted fillers are spherical aluminum oxide (Al2O3), linear carbon fiber and boron nitride sheets, which can be considered as zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) fillers respectively. We also prepared the silver-modified fillers and investigated the influence on the formation of heat conduction pathways and interfacial thermal resistance of different shaped fillers. An obvious increment in thermal conductivity of the composite with silver-modified fillers was observed compared to the composite with pristine fillers. Furthermore, through the practical thermal management performance investigation, we found the thermal conductivity increment did improve the actual heat transfer performance of composite elastomers functioning as thermal interface materials","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49129101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-10DOI: 10.3389/fther.2022.907873
Shuanyang Zhang, Shun Liu, Hongtao Xu, Y. Mao, Ke Wang
Reasonable flow channel designs play a significant role in improving the performance of proton exchange membrane fuel cells (PEMFC). The effect of the zigzag flow channels with three different numbers of turns on the performance of PEMFC was investigated in this paper. The polarization curves, molar concentration of oxygen and water, and power density were analyzed, and the numerical results showed that the overall performance of the zigzag flow channels was significantly better than that of the conventional parallel flow channel. With the increase of the number of turns from 3 to 9, the performance of PEMFC was gradually improved, the diffusion capacity of oxygen to the interface of the electrochemical reaction was also promoted, and the low oxygen concentration regions were gradually reduced. When the number of turns was 9, the current density of PEMFC was 8.85% higher than that of the conventional parallel channel at the operating voltage of 0.4 V, and the oxygen non-uniformity at the between gas diffusion layer (GDL) and catalyst layer (CL) interface was the minimum with a value of 0.51. In addition, the molar concentration of water in the channel also decreased. Due to the relatively large resistance of the zigzag flow channels, the maximum pressure drop of the zigzag flow channel was 263.5 Pa, which was also conducive to the improvement of the drainage effect of the conventional parallel flow channel. With the increase of the number of turns in the zigzag channel, the pressure drop and parasitic power density gradually increased. The 9-zigzag flow channel obtained the maximum pressure drop and net power density, which were 263.5 Pa and 2995.6 W/m2, respectively.
{"title":"Numerical Investigation on the Performance of Proton Exchange Membrane Fuel Cell With Zigzag Flow Channels","authors":"Shuanyang Zhang, Shun Liu, Hongtao Xu, Y. Mao, Ke Wang","doi":"10.3389/fther.2022.907873","DOIUrl":"https://doi.org/10.3389/fther.2022.907873","url":null,"abstract":"Reasonable flow channel designs play a significant role in improving the performance of proton exchange membrane fuel cells (PEMFC). The effect of the zigzag flow channels with three different numbers of turns on the performance of PEMFC was investigated in this paper. The polarization curves, molar concentration of oxygen and water, and power density were analyzed, and the numerical results showed that the overall performance of the zigzag flow channels was significantly better than that of the conventional parallel flow channel. With the increase of the number of turns from 3 to 9, the performance of PEMFC was gradually improved, the diffusion capacity of oxygen to the interface of the electrochemical reaction was also promoted, and the low oxygen concentration regions were gradually reduced. When the number of turns was 9, the current density of PEMFC was 8.85% higher than that of the conventional parallel channel at the operating voltage of 0.4 V, and the oxygen non-uniformity at the between gas diffusion layer (GDL) and catalyst layer (CL) interface was the minimum with a value of 0.51. In addition, the molar concentration of water in the channel also decreased. Due to the relatively large resistance of the zigzag flow channels, the maximum pressure drop of the zigzag flow channel was 263.5 Pa, which was also conducive to the improvement of the drainage effect of the conventional parallel flow channel. With the increase of the number of turns in the zigzag channel, the pressure drop and parasitic power density gradually increased. The 9-zigzag flow channel obtained the maximum pressure drop and net power density, which were 263.5 Pa and 2995.6 W/m2, respectively.","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49593730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-05-05DOI: 10.3389/fther.2022.900910
Zixuan Wang, Linhao Fan, Siyuan Wu, Chasen Tongsh, Yanyi Zhang, Zirong Yang, Qing Du, Dong Hao, Feikun Zhou, K. Jiao
Using metal foam as a flow field structure is an attractive route to improve the performance of open-cathode PEMFC. Metal foam has shown great potential in improving the uniformity of reactants, but optimized structure parameters that can more effectively transfer gas and remove excess water are needed. Here we experimentally investigate the effect of metal foam structure parameters on cell performance using polarization curves, power density curves, and electrochemical impedance spectrum (EIS) measurements. By optimizing the pore density, thickness, and compression ratio of the metal foam, the performance of the fuel cell is improved by 49.8%, 42.1%, and 7.3%, respectively. The optimum structure value of metal foam is the pore density of 40 PPI, the thickness of 2.4 mm, and the compression ratio of 4:2.4. In this configuration, the cell could achieve a maximum power density of 0.485 W cm−2. The findings of this work are beneficial for the application of metal foams in open-cathode PEMFC.
使用金属泡沫作为流场结构是提高开阴极PEMFC性能的一条有吸引力的途径。金属泡沫在提高反应物的均匀性方面显示出巨大的潜力，但需要优化结构参数，以更有效地转移气体和去除多余的水。在这里，我们使用极化曲线、功率密度曲线和电化学阻抗谱（EIS）测量，实验研究了金属泡沫结构参数对电池性能的影响。通过优化金属泡沫的孔密度、厚度和压缩比，燃料电池的性能分别提高了49.8%、42.1%和7.3%。金属泡沫的最佳结构值是孔密度为40PPI，厚度为2.4mm，压缩比为4:2.4。在这种配置中，电池可以实现0.485 W cm−2的最大功率密度。这项工作的发现有利于金属泡沫在开阴极PEMFC中的应用。
{"title":"Experimental Optimization of Metal Foam Structural Parameters to Improve the Performance of Open-Cathode Proton Exchange Membrane Fuel Cell","authors":"Zixuan Wang, Linhao Fan, Siyuan Wu, Chasen Tongsh, Yanyi Zhang, Zirong Yang, Qing Du, Dong Hao, Feikun Zhou, K. Jiao","doi":"10.3389/fther.2022.900910","DOIUrl":"https://doi.org/10.3389/fther.2022.900910","url":null,"abstract":"Using metal foam as a flow field structure is an attractive route to improve the performance of open-cathode PEMFC. Metal foam has shown great potential in improving the uniformity of reactants, but optimized structure parameters that can more effectively transfer gas and remove excess water are needed. Here we experimentally investigate the effect of metal foam structure parameters on cell performance using polarization curves, power density curves, and electrochemical impedance spectrum (EIS) measurements. By optimizing the pore density, thickness, and compression ratio of the metal foam, the performance of the fuel cell is improved by 49.8%, 42.1%, and 7.3%, respectively. The optimum structure value of metal foam is the pore density of 40 PPI, the thickness of 2.4 mm, and the compression ratio of 4:2.4. In this configuration, the cell could achieve a maximum power density of 0.485 W cm−2. The findings of this work are beneficial for the application of metal foams in open-cathode PEMFC.","PeriodicalId":73110,"journal":{"name":"Frontiers in thermal engineering","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48744904","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-29DOI: 10.3389/fther.2022.882941
L. Dombrovsky, A. Kokhanovsky
The observed gradual change in the Earth’s climate most noticeably affects the snow cover and ice sheets in the polar regions, especially during the long polar summer, when solar radiation leads to considerable increase in temperature and partial melting at some distance from the snow or ice surface. This effect, which in the polar regions is more pronounced in the snow cover, deserves serious attention as an important geophysical problem. In this article, for the first time, a theoretical analysis is made of the conditions under which the absorption of directional radiation penetrating a weakly absorbing scattering medium has a maximum at some distance from the illuminated surface. It is shown that the maximum absorption of radiation inside an optically thick medium exists only at illumination angles less than 60° from the normal. An analytical solution was obtained that gives both the magnitude of this maximum absorption and its depth below the illuminated surface. Calculations of solar radiation transfer and heat propagation in the snow layer are also performed. Various experimental data on the ice absorption index in the visible range are taken into account when determining the optical properties of snow. To calculate the transient temperature profile in the snow layer, the heat conduction equation with volumetric absorption of radiation is solved. The boundary conditions take into account the variation of solar irradiation, convective heat transfer, and radiative cooling of snow in the infrared transparency window of the cloudless atmosphere. The calculations show that the radiative cooling should be taken into account even during the polar summer.
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Pub Date : 2022-04-26DOI: 10.3389/fther.2022.862070
L. Dombrovsky
It is known that the study of the processes of heat generation and propagation, as well as its transformation into other types of energy, led to the discovery of fundamental physical laws. We should remember, first of all, the laws of thermal radiation, the discovery of which just over a century ago radically changed physics as a science and became the basis of incredible technical advances. The revolution in theoretical physics has greatly accelerated research in heat transfer and various applications, especially in thermal engineering. Textbooks usually distinguish three ways of heat transfer: conduction, convection, and thermal radiation. However, attempts to solve real problems show that we are usually dealing with combined heat transfer, when different modes of heat transfer interact with each other. In my opinion, thermal radiation is closer to fundamental science and appears to be a more global phenomenon than other modes of heat transfer. It is not even the fact that life on our planet exists because of thermal radiation from the Sun, and this radiation extends 150million kilometers to reach the Earth. Contrary to popular belief, thermal radiation turns out to be important at any temperature and at any distance, and its spectrum includes the microwave range used in remote sensing of the ocean surface. This explains why we focus on radiative and combined heat transfer, and the variety of problems involved is so great. The research topics under consideration are mainly related to various problems of radiation transfer in semitransparent scattering media. Such media are, for example, gases or liquids with suspended particles, as well as various dispersed materials and solids with microcracks or bubbles. Natural objects of study include the Earth’s atmosphere and ocean, snow and ice, powders or dust and ordinary sand, and even biological tissues with optically heterogeneous living cells. In thermal engineering these are combustion products containing soot and fly ash particles, porous ceramics and heat-shielding materials, particles in thermochemical reactors and melt droplets from a possible severe nuclear reactor accident. A far from complete set of given examples leaves no doubt about the practical importance of studying radiation propagation in scattering media. Therefore, our editorial team was formed mainly from researchers working in the field of radiative and combined heat transfer in disperse systems. The classical theory of radiative transfer in such media is based on the integrodifferential equation, which was independently derived early last century by Orest Khvolson and Subrahmanyan Chandrasekhar in connection with the study of radiative transfer in stellar photospheres (Chandrasekhar 1960; Rosenberg 1977). A modern systematic account of the theory of radiative heat transfer can be found in textbooks by Howell et al. (2021) and Modest and Mazumder (2021), and an engineering approach tomodeling radiative and combined heat transfer
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