Pub Date : 2024-11-08DOI: 10.1016/j.ijthermalsci.2024.109522
Junhong Si , Zihao Zhao , Yiqiao Wang , Huan Mao
Coal oxidation in the goaf generates heat accumulation influenced by airflow, leading to heat transfer within the porous coal structure. This study experimentally investigates the heat transfer characteristics of coal under convective conditions. A temperature migration rate measurement device was developed, and a formula for calculating the temperature migration rate was derived using the steady-state heat conduction differential equation and experimental data. The study examines the effects of temperature and airflow on the temperature migration rate and heat transfer characteristics. The experimental results indicate that the heat transfer effect of coal at low temperatures is minimal and volatile. As the temperature increases, efficiency improves, and heat transfer stabilizes. Airflow facilitates coal's heat transfer, causing the temperature generated by coal oxidation to concentrate on the downwind side. Additionally, airflow inhibits coal oxidation at low temperatures, while high temperatures promote it. Furthermore, the temperature migration rate of coal decreases with increasing temperature, initially decreases and then increases with rising airflow at low temperatures, whereas the opposite trend is observed at high temperatures.
{"title":"Study on heat transfer law of low temperature oxidation of coal under convection condition","authors":"Junhong Si , Zihao Zhao , Yiqiao Wang , Huan Mao","doi":"10.1016/j.ijthermalsci.2024.109522","DOIUrl":"10.1016/j.ijthermalsci.2024.109522","url":null,"abstract":"<div><div>Coal oxidation in the goaf generates heat accumulation influenced by airflow, leading to heat transfer within the porous coal structure. This study experimentally investigates the heat transfer characteristics of coal under convective conditions. A temperature migration rate measurement device was developed, and a formula for calculating the temperature migration rate was derived using the steady-state heat conduction differential equation and experimental data. The study examines the effects of temperature and airflow on the temperature migration rate and heat transfer characteristics. The experimental results indicate that the heat transfer effect of coal at low temperatures is minimal and volatile. As the temperature increases, efficiency improves, and heat transfer stabilizes. Airflow facilitates coal's heat transfer, causing the temperature generated by coal oxidation to concentrate on the downwind side. Additionally, airflow inhibits coal oxidation at low temperatures, while high temperatures promote it. Furthermore, the temperature migration rate of coal decreases with increasing temperature, initially decreases and then increases with rising airflow at low temperatures, whereas the opposite trend is observed at high temperatures.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"209 ","pages":"Article 109522"},"PeriodicalIF":4.9,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652623","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 : 2024-10-30DOI: 10.1016/j.ijthermalsci.2024.109505
Haoran Jiang, Yong Hu, Yong Jiang, Ke Yu, Rong Qiu
As industrialization continues to deepen, polymers have become ubiquitous in daily life. However, their flammable characteristics pose significant safety risks. Therefore, supporting the global goal of sustainable development necessitates the development of high-performance, environmentally friendly flame retardants. Biomass phytic acid (PA) has emerged as a promising option because of its high phosphorus content and excellent biocompatibility. However, its combustion behaviors and chemical kinetic mechanisms remain unclear. In this study, quantum chemical calculation methods were used to construct a detailed PA chemical reaction kinetic model. A series of experiments were conducted to validate the model and evaluate PA's flame suppression effect. Utilizing a counterflow flame burner and particle image velocimetry (PIV), the inhibitory effect of various PA concentrations was examined based on the laminar flame speed of CH4/PA/Air mixture. The results revealed that a merely 0.2 % addition of PA could reduce the laminar flame speed by 38.9 %, demonstrating its significant flame suppression effect. Building on the foundational GRI-Mech 3.0 and integrating PA's pyrolysis and reaction mechanism, this study developed for the first time a detailed chemical model of CH4/PA/Air combustion. This model integrated PA's thermal decomposition module and thermodynamic data via ab-initio quantum chemical calculations, thereby accurately predicting global kinetic indicators such as laminar flame speed. Results suggested that the key reactions, such as PO2+H + M→HOPO + M, HOPO2+H→PO2+H2O, and HOPO + OH→PO2+H2O primarily influenced the laminar flame speed. Moreover, the CFD simulation elucidated the complex interaction between PA and flame structures. A detailed analysis of the spatial distribution of key parameters such as temperature, combustion radicals, and effective inhibition radicals unveiled the PA's flame suppression mechanism in support of the practical application of this eco-friendly flame retardant.
随着工业化的不断深入，聚合物在日常生活中无处不在。然而，它们的易燃特性带来了极大的安全风险。因此，要支持全球可持续发展目标，就必须开发高性能的环保型阻燃剂。生物质植酸（PA）因其高磷含量和出色的生物相容性而成为一种前景广阔的选择。然而，其燃烧行为和化学动力学机制仍不清楚。本研究采用量子化学计算方法构建了详细的 PA 化学反应动力学模型。为了验证该模型并评估 PA 的火焰抑制效果，进行了一系列实验。利用逆流火焰燃烧器和粒子图像测速仪（PIV），根据 CH4/PA/Air 混合物的层流火焰速度考察了不同浓度 PA 的抑制效果。结果表明，仅添加 0.2% 的 PA 就能使层流火焰速度降低 38.9%，显示了其显著的火焰抑制效果。本研究以 GRI-Mech 3.0 为基础，结合 PA 的热分解和反应机理，首次建立了 CH4/PA/Air 燃烧的详细化学模型。该模型通过非原位量子化学计算，整合了 PA 的热分解模块和热力学数据，从而准确预测了层流火焰速度等全局动力学指标。结果表明，PO2+H+M→HOPO+M、HOPO2+H→PO2+H2O、HOPO+OH→PO2+H2O 等关键反应主要影响层焰速度。此外，CFD 模拟还阐明了 PA 与火焰结构之间复杂的相互作用。对温度、燃烧自由基和有效抑制自由基等关键参数空间分布的详细分析揭示了 PA 的火焰抑制机理，为这种环保型阻燃剂的实际应用提供了支持。
{"title":"Revealing the flame inhibition effect of phytic acid (PA) by PIV measurements and detailed chemical kinetic modeling of counterflow CH4/PA/air flames","authors":"Haoran Jiang, Yong Hu, Yong Jiang, Ke Yu, Rong Qiu","doi":"10.1016/j.ijthermalsci.2024.109505","DOIUrl":"10.1016/j.ijthermalsci.2024.109505","url":null,"abstract":"<div><div>As industrialization continues to deepen, polymers have become ubiquitous in daily life. However, their flammable characteristics pose significant safety risks. Therefore, supporting the global goal of sustainable development necessitates the development of high-performance, environmentally friendly flame retardants. Biomass phytic acid (PA) has emerged as a promising option because of its high phosphorus content and excellent biocompatibility. However, its combustion behaviors and chemical kinetic mechanisms remain unclear. In this study, quantum chemical calculation methods were used to construct a detailed PA chemical reaction kinetic model. A series of experiments were conducted to validate the model and evaluate PA's flame suppression effect. Utilizing a counterflow flame burner and particle image velocimetry (PIV), the inhibitory effect of various PA concentrations was examined based on the laminar flame speed of CH<sub>4</sub>/PA/Air mixture. The results revealed that a merely 0.2 % addition of PA could reduce the laminar flame speed by 38.9 %, demonstrating its significant flame suppression effect. Building on the foundational GRI-Mech 3.0 and integrating PA's pyrolysis and reaction mechanism, this study developed for the first time a detailed chemical model of CH<sub>4</sub>/PA/Air combustion. This model integrated PA's thermal decomposition module and thermodynamic data via ab-initio quantum chemical calculations, thereby accurately predicting global kinetic indicators such as laminar flame speed. Results suggested that the key reactions, such as PO<sub>2</sub>+H + M→HOPO + M, HOPO<sub>2</sub>+H→PO<sub>2</sub>+H<sub>2</sub>O, and HOPO + OH→PO<sub>2</sub>+H<sub>2</sub>O primarily influenced the laminar flame speed. Moreover, the CFD simulation elucidated the complex interaction between PA and flame structures. A detailed analysis of the spatial distribution of key parameters such as temperature, combustion radicals, and effective inhibition radicals unveiled the PA's flame suppression mechanism in support of the practical application of this eco-friendly flame retardant.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109505"},"PeriodicalIF":4.9,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561211","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 : 2024-10-30DOI: 10.1016/j.ijthermalsci.2024.109481
KeWei Song , Zhen Tian , Xiang Wu , Qiang Zhang , Kun Zhang , BingDong Gu
A new configuration featuring an inner oval tube with alternating twist directions is proposed to improve the thermal performance of double-tube heat exchangers. This design enhances the heat transfer efficiency by inducing longitudinal vortices within the annular space, thereby disrupting the boundary layer on the heat transfer surface, promoting fluid mixing, and significantly augmenting heat transfer. Numerical simulations were conducted to investigate the effects of alternating twist directions of the inner oval tube on thermal performance. The results demonstrate that alternating twist direction of the inner tube creates more pronounced vortices, significantly enhances heat transfer performance compared with the conventional tubes. This novel oval tube led to a substantial enhancement of up to 173.6 % in the Nu, with a corresponding increase of 96.4 % in the f. At Re = 2600, the highest thermal performance factor of the reported annular tube with an alternately twisted oval inner tube can reach up to 2.18, indicating a 118 % improvement in overall heat transfer performance. Fitted correlations for Nu and f are provided to facilitate engineering applications.
为了提高双管热交换器的热性能，我们提出了一种新的结构，其特点是内椭圆管具有交替的扭曲方向。这种设计通过在环形空间内诱发纵向涡流来提高传热效率，从而破坏传热表面的边界层，促进流体混合，显著增强传热效果。我们进行了数值模拟，以研究椭圆形内管交替扭曲方向对热性能的影响。结果表明，内管的交替扭曲方向会产生更明显的涡流，与传统管道相比，能显著提高传热性能。在 Re = 2600 条件下，报告的带有交替扭曲椭圆形内管的环形管的最高热性能系数可达 2.18，表明整体传热性能提高了 118%。为方便工程应用，提供了 Nu 和 f 的拟合相关性。
{"title":"Thermal characteristics of a double-tube heat exchanger with different twist directions of the inner oval tube","authors":"KeWei Song , Zhen Tian , Xiang Wu , Qiang Zhang , Kun Zhang , BingDong Gu","doi":"10.1016/j.ijthermalsci.2024.109481","DOIUrl":"10.1016/j.ijthermalsci.2024.109481","url":null,"abstract":"<div><div>A new configuration featuring an inner oval tube with alternating twist directions is proposed to improve the thermal performance of double-tube heat exchangers. This design enhances the heat transfer efficiency by inducing longitudinal vortices within the annular space, thereby disrupting the boundary layer on the heat transfer surface, promoting fluid mixing, and significantly augmenting heat transfer. Numerical simulations were conducted to investigate the effects of alternating twist directions of the inner oval tube on thermal performance. The results demonstrate that alternating twist direction of the inner tube creates more pronounced vortices, significantly enhances heat transfer performance compared with the conventional tubes. This novel oval tube led to a substantial enhancement of up to 173.6 % in the <em>Nu</em>, with a corresponding increase of 96.4 % in the <em>f</em>. At <em>Re</em> = 2600, the highest thermal performance factor of the reported annular tube with an alternately twisted oval inner tube can reach up to 2.18, indicating a 118 % improvement in overall heat transfer performance. Fitted correlations for <em>Nu</em> and <em>f</em> are provided to facilitate engineering applications.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109481"},"PeriodicalIF":4.9,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561212","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 : 2024-10-30DOI: 10.1016/j.ijthermalsci.2024.109504
Ghassem Heidarinejad, Mohammadreza Eftekhari, Mohammad Safarzadeh, Mohammad Zabetian Targhi
The primary objective of this study is to examine various fire scenarios occurring within storage tanks containing three standard refinery-produced fuels: gasoline, kerosene, and crude oil. Additionally, the aim is to analyze the emissions of CO and CO₂ pollutants, the temperature of hot gases, and the radiation emissions resulting from the combustion of fuel tanks, considering real-scale tanks with diameters of 25, 50, and 75 m. This research introduces innovation by concurrently comparing the abovementioned hazards under varying environmental conditions, considering the presence or absence of wind as a critical factor influencing hazard propagation. In addition, the radiation effect is identified as the most significant hazard near the storage tanks. Furthermore, wind can intensify radiation levels in the direction of its movement, with a noticeable impact. Increasing wind speed from zero to 15 m/s results in a 1.5-fold increase in the safety distance. Without wind, CO and CO2, along with high gas temperatures, do not pose destructive threats. However, wind causes these hazards to extend closer to the Earth's surface. Under wind speeds of 15 m/s, these hazards reach a height of approximately 5 m above the ground. Notably, gasoline fuel is recognized as more perilous.
{"title":"Investigating radiation, toxic and hot gases fire hazards in large-scale storage tanks for oil derivatives with and without wind conditions","authors":"Ghassem Heidarinejad, Mohammadreza Eftekhari, Mohammad Safarzadeh, Mohammad Zabetian Targhi","doi":"10.1016/j.ijthermalsci.2024.109504","DOIUrl":"10.1016/j.ijthermalsci.2024.109504","url":null,"abstract":"<div><div>The primary objective of this study is to examine various fire scenarios occurring within storage tanks containing three standard refinery-produced fuels: gasoline, kerosene, and crude oil. Additionally, the aim is to analyze the emissions of CO and CO₂ pollutants, the temperature of hot gases, and the radiation emissions resulting from the combustion of fuel tanks, considering real-scale tanks with diameters of 25, 50, and 75 m. This research introduces innovation by concurrently comparing the abovementioned hazards under varying environmental conditions, considering the presence or absence of wind as a critical factor influencing hazard propagation. In addition, the radiation effect is identified as the most significant hazard near the storage tanks. Furthermore, wind can intensify radiation levels in the direction of its movement, with a noticeable impact. Increasing wind speed from zero to 15 m/s results in a 1.5-fold increase in the safety distance. Without wind, CO and CO<sub>2</sub>, along with high gas temperatures, do not pose destructive threats. However, wind causes these hazards to extend closer to the Earth's surface. Under wind speeds of 15 m/s, these hazards reach a height of approximately 5 m above the ground. Notably, gasoline fuel is recognized as more perilous.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109504"},"PeriodicalIF":4.9,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561210","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 : 2024-10-30DOI: 10.1016/j.ijthermalsci.2024.109461
Lili Xia , Hamid Montazeri , Bert Blocken
CFD simulation of droplet evaporation in turbulent flows is challenging as the accuracy and reliability of the results strongly depend on the available sub-models and their modeling parameters. This study presents a systematic sensitivity analysis focused on the impact of the most widely used discrete random walk (DRW) model, the constant time scale coefficient (CL), the turbulence model, and the drag coefficient model. CFD simulations with the Eulerian-Lagrangian approach are employed. The analysis is based on grid-sensitivity analysis and validation with measurements of spray evaporation in a heated turbulent airflow. The results show that using the DRW model leads to a good agreement between the CFD results and the experimental data of droplet size and droplet mean velocity, attributed to the turbulent fluctuations inducing droplet dispersion. The best performance is observed for the standard k-ε turbulence model with CL = 0.30 and 0.45. This is mainly attributed to the reasonable interaction time between droplets and turbulent eddies at these CL values. The three drag coefficient models (i.e., Spherical, Ischii-Zuber, and Grace) lead to similar results due to the low droplet Reynolds number.
{"title":"On the accuracy of Eulerian-Lagrangian CFD simulations for spray evaporation in turbulent flow","authors":"Lili Xia , Hamid Montazeri , Bert Blocken","doi":"10.1016/j.ijthermalsci.2024.109461","DOIUrl":"10.1016/j.ijthermalsci.2024.109461","url":null,"abstract":"<div><div>CFD simulation of droplet evaporation in turbulent flows is challenging as the accuracy and reliability of the results strongly depend on the available sub-models and their modeling parameters. This study presents a systematic sensitivity analysis focused on the impact of the most widely used discrete random walk (DRW) model, the constant time scale coefficient (C<sub>L</sub>), the turbulence model, and the drag coefficient model. CFD simulations with the Eulerian-Lagrangian approach are employed. The analysis is based on grid-sensitivity analysis and validation with measurements of spray evaporation in a heated turbulent airflow. The results show that using the DRW model leads to a good agreement between the CFD results and the experimental data of droplet size and droplet mean velocity, attributed to the turbulent fluctuations inducing droplet dispersion. The best performance is observed for the standard k-ε turbulence model with C<sub>L</sub> = 0.30 and 0.45. This is mainly attributed to the reasonable interaction time between droplets and turbulent eddies at these C<sub>L</sub> values. The three drag coefficient models (i.e., Spherical, Ischii-Zuber, and Grace) lead to similar results due to the low droplet Reynolds number.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109461"},"PeriodicalIF":4.9,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561213","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 : 2024-10-29DOI: 10.1016/j.ijthermalsci.2024.109495
Zhixuan Liang , Haiping Wen , Qiming Lv , Wen Su , Changhong Wang
This paper analyses the characteristics of temperature, velocity and pressure loss of various channel configurations with identical Reynolds Number Re. A comparative analysis is conducted to assess substrate temperature and convection heat dissipation area. Furthermore, the optimal composite microchannel heat sink design is identified leveraging entropy generation theory and a comprehensive performance evaluation. Simulation results reveal that the pressure loss of microchannel with rectangular cross-sectional cavities (MC-RCSC) is the lowest whereas microchannel with ribs and secondary channels (MC-RSOC) experiences the highest. The flow rate of MC-RSOC is uniform and better mixed with the aid of the backflow phenomenon. In terms of average outlet temperature, in descending order, the microchannels are ranked as follows: MC-RCSC > microchannel with rectangular grooves and side wall ribs (MC-RGSW) > microchannel with rectangular grooves and alternating ribs (MC-RGA) > microchannel with rectangular grooves (MC-RG) > MC-RSOC. Regarding the performance factor, , of MC-RSOC, MC-RCSC and MC-RG are all greater than 1, while the of MC-RGA and MC-RGSW are less than 1 at low Re. The of MC-RSOC is the highest. Flow rate is found to have a marginal impact on the temperature drop. is an order of magnitude smaller than , of MC-RSOC is the smallest. The comprehensive comparison of entropy generation and performance shows that MC-RSOC is the best composite structure.
{"title":"Comparative performance analysis of microchannel heat sink with different geometric structures","authors":"Zhixuan Liang , Haiping Wen , Qiming Lv , Wen Su , Changhong Wang","doi":"10.1016/j.ijthermalsci.2024.109495","DOIUrl":"10.1016/j.ijthermalsci.2024.109495","url":null,"abstract":"<div><div>This paper analyses the characteristics of temperature, velocity and pressure loss of various channel configurations with identical Reynolds Number Re. A comparative analysis is conducted to assess substrate temperature and convection heat dissipation area. Furthermore, the optimal composite microchannel heat sink design is identified leveraging entropy generation theory and a comprehensive performance evaluation. Simulation results reveal that the pressure loss of microchannel with rectangular cross-sectional cavities (MC-RCSC) is the lowest whereas microchannel with ribs and secondary channels (MC-RSOC) experiences the highest. The flow rate of MC-RSOC is uniform and better mixed with the aid of the backflow phenomenon. In terms of average outlet temperature, in descending order, the microchannels are ranked as follows: MC-RCSC > microchannel with rectangular grooves and side wall ribs (MC-RGSW) > microchannel with rectangular grooves and alternating ribs (MC-RGA) > microchannel with rectangular grooves (MC-RG) > MC-RSOC. Regarding the performance factor, <span><math><mrow><mi>P</mi><mi>f</mi></mrow></math></span>, of MC-RSOC, MC-RCSC and MC-RG are all greater than 1, while the <span><math><mrow><mi>P</mi><mi>f</mi></mrow></math></span> of MC-RGA and MC-RGSW are less than 1 at low Re. The <span><math><mrow><mi>P</mi><mi>f</mi></mrow></math></span> of MC-RSOC is the highest. Flow rate is found to have a marginal impact on the temperature drop. <span><math><mrow><msub><mi>S</mi><mrow><mi>g</mi><mi>e</mi><mi>n</mi><mo>,</mo><mo>Δ</mo><mi>P</mi></mrow></msub></mrow></math></span> is an order of magnitude smaller than <span><math><mrow><msub><mi>S</mi><mrow><mi>g</mi><mi>e</mi><mi>n</mi><mo>,</mo><mo>Δ</mo><mi>T</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msub><mi>S</mi><mrow><mi>g</mi><mi>e</mi><mi>n</mi></mrow></msub></mrow></math></span> of MC-RSOC is the smallest. The comprehensive comparison of entropy generation and performance shows that MC-RSOC is the best composite structure.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109495"},"PeriodicalIF":4.9,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142539306","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 : 2024-10-28DOI: 10.1016/j.ijthermalsci.2024.109494
Huolei Feng , Wenyi Ma , Yushan Ni
The passive thermal-electric ultra-conductive metamaterials (PTUM) consisting of bulk natural materials are reported, which possess the local pre-controlled thermal-electric ultra-conductivities without extra energy payloads. Based on the local resistances regulated by the vertical transport channels, the thermal-electric effective parameters at the circular channel-interphase region are derived. Then, we present a method to make the designed channel suitable for both tempetature and electric potential fields simultaneously and analyze some manipulation factors modulating the thermal-electric ultra-conductivities. Based on the modulation effects, the PTUM with different pre-controlled parameters could be constructed by changing the height of the channels, which are demonstrated by the numerical simulations. Additionally, in order to validate the reliability of the construction theories, the normalized theoretical temperatures and electric potentials are provided to make a fair contrast with the normalized corresponding simulated values. The good coincidence between the simulated values and theoretical solutions indicates that we can realize the local thermal-electric ultra-conductivities by introducing the channels with different heights. Furthermore, we present some applications of pre-controlled PTUM to reveal the passive thermal-electric ultra-conductive effects and the utilization directions, such as the thermal-electric ultra-conductive metal plate and the ultra-conductive thermal-electric concentrator and cloak. This paper may provide a method to achieve the passive ultra-conductive metamaterials suitable for both temperature and electric potential fields simultaneously using the natural materials in general application environments.
{"title":"Design of the pre-controlled thermal-electric ultra-conductive metamaterials without extra energy payloads","authors":"Huolei Feng , Wenyi Ma , Yushan Ni","doi":"10.1016/j.ijthermalsci.2024.109494","DOIUrl":"10.1016/j.ijthermalsci.2024.109494","url":null,"abstract":"<div><div>The passive thermal-electric ultra-conductive metamaterials (PTUM) consisting of bulk natural materials are reported, which possess the local pre-controlled thermal-electric ultra-conductivities without extra energy payloads. Based on the local resistances regulated by the vertical transport channels, the thermal-electric effective parameters at the circular channel-interphase region are derived. Then, we present a method to make the designed channel suitable for both tempetature and electric potential fields simultaneously and analyze some manipulation factors modulating the thermal-electric ultra-conductivities. Based on the modulation effects, the PTUM with different pre-controlled parameters could be constructed by changing the height of the channels, which are demonstrated by the numerical simulations. Additionally, in order to validate the reliability of the construction theories, the normalized theoretical temperatures and electric potentials are provided to make a fair contrast with the normalized corresponding simulated values. The good coincidence between the simulated values and theoretical solutions indicates that we can realize the local thermal-electric ultra-conductivities by introducing the channels with different heights. Furthermore, we present some applications of pre-controlled PTUM to reveal the passive thermal-electric ultra-conductive effects and the utilization directions, such as the thermal-electric ultra-conductive metal plate and the ultra-conductive thermal-electric concentrator and cloak. This paper may provide a method to achieve the passive ultra-conductive metamaterials suitable for both temperature and electric potential fields simultaneously using the natural materials in general application environments.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109494"},"PeriodicalIF":4.9,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142539406","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 : 2024-10-28DOI: 10.1016/j.ijthermalsci.2024.109475
Suhas Jagtap, Manish Mishra
The present study is a 2-D numerical study which discusses the thermohydraulic performance of packed bed duct under local thermal non-equilibrium and steady state conditions exposed to forced convection boundaries (BC-6). The numerical model is well validated with the experimental work reported in the literature and found to be accurate enough to perform further parametric investigations. The analysis is done to see the effect of different ball diameter (5 mm, 9 mm and 11 mm), bed porosity, heat transfer fluid (air, water and engine oil - Pr = 0.70–645) and ball material (EPS, steel and bronze) on heat transfer and fluid flow characteristics in turbulent flow region of Reynolds number ranging from 900 to 14,320. The numerical results obtained using commercial CFD software COMSOL shows that, the heat transfer coefficient and pressure drop in packed bed increases with increase in ball diameter, thermal conductivity of ball and bed porosity which is exactly reverse as reported in literature for BC-1 to BC-5. The maximum thermal performance factor with bronze particles is 2.45 and 24.5 times more than stainless steel and EPS particles respectively for larger particle size and bed porosity. Engine oil exhibits significantly higher heat transfer coefficient (9.7 × 105 W/m2K) and pressure drop (3.3 × 106 Pa) compared to water (40,126 W/m2K and 2028 Pa) and air (600 W/m2K and 250 Pa) respectively. Overall, the combination of water as heat transfer fluid along with bronze particles of larger diameter and larger bed porosity emerges as the optimal choice for enhancing heat transfer in the packed duct exposed to forced convection boundary condition BC-6.
{"title":"Numerical investigations of heat transfer and pressure drop in packed bed duct exposed to forced convection boundaries under local thermal non-equilibrium conditions","authors":"Suhas Jagtap, Manish Mishra","doi":"10.1016/j.ijthermalsci.2024.109475","DOIUrl":"10.1016/j.ijthermalsci.2024.109475","url":null,"abstract":"<div><div>The present study is a 2-D numerical study which discusses the thermohydraulic performance of packed bed duct under local thermal non-equilibrium and steady state conditions exposed to forced convection boundaries (BC-6). The numerical model is well validated with the experimental work reported in the literature and found to be accurate enough to perform further parametric investigations. The analysis is done to see the effect of different ball diameter (5 mm, 9 mm and 11 mm), bed porosity, heat transfer fluid (air, water and engine oil - P<sub>r</sub> = 0.70–645) and ball material (EPS, steel and bronze) on heat transfer and fluid flow characteristics in turbulent flow region of Reynolds number ranging from 900 to 14,320. The numerical results obtained using commercial CFD software COMSOL shows that, the heat transfer coefficient and pressure drop in packed bed increases with increase in ball diameter, thermal conductivity of ball and bed porosity which is exactly reverse as reported in literature for BC-1 to BC-5. The maximum thermal performance factor with bronze particles is 2.45 and 24.5 times more than stainless steel and EPS particles respectively for larger particle size and bed porosity. Engine oil exhibits significantly higher heat transfer coefficient (9.7 × 10<sup>5</sup> W/m<sup>2</sup>K) and pressure drop (3.3 × 10<sup>6</sup> Pa) compared to water (40,126 W/m<sup>2</sup>K and 2028 Pa) and air (600 W/m<sup>2</sup>K and 250 Pa) respectively. Overall, the combination of water as heat transfer fluid along with bronze particles of larger diameter and larger bed porosity emerges as the optimal choice for enhancing heat transfer in the packed duct exposed to forced convection boundary condition BC-6.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109475"},"PeriodicalIF":4.9,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142539305","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 : 2024-10-24DOI: 10.1016/j.ijthermalsci.2024.109489
Yu Wang , Chengming Xiao , Chiara Bedon
Integrating photovoltaic (PV) panels with different tilt angles in building envelopes or roofs is widely employed for environmental sustainability. However, little is known about the influence of different tilt angles on the thermal failure of the photovoltaic façades or roofs in fire conditions. A total of 15 four-edge shielded PV panels (300 × 300 × 4.7 mm3), with five different inclinations of 0°, 15°, 30°, 45° and 60°, were heated to fail using a uniform radiant panel. Measurements were taken to track glass thermal breakage, surface temperatures, incident heat flux and failure characteristics. The glass fracture and pyrolysis of the internal thermoplastic materials were observed under thermal radiation. The average breakage time of glass in PV panels showed an increasing trend with increasing inclination of the PV panels. Moreover, when the PV panels were tilted beyond 30°, the time to failure increased more significantly. The maximum temperature difference and heat flux that the PV panels can withstand were primarily measured within the range of 61–84 °C and 8–15 kW/m2, respectively. Finally, the test results were simulated by a finite element method (FEM) model, calculating the heat transfer and thermal stress of PV panels: the average errors concerning temperature distributions and failure times were smaller than 15 % compared with the experimental results.
{"title":"Performance of photovoltaic panels with different inclinations under uniform thermal loading","authors":"Yu Wang , Chengming Xiao , Chiara Bedon","doi":"10.1016/j.ijthermalsci.2024.109489","DOIUrl":"10.1016/j.ijthermalsci.2024.109489","url":null,"abstract":"<div><div>Integrating photovoltaic (PV) panels with different tilt angles in building envelopes or roofs is widely employed for environmental sustainability. However, little is known about the influence of different tilt angles on the thermal failure of the photovoltaic façades or roofs in fire conditions. A total of 15 four-edge shielded PV panels (300 × 300 × 4.7 mm<sup>3</sup>), with five different inclinations of 0°, 15°, 30°, 45° and 60°, were heated to fail using a uniform radiant panel. Measurements were taken to track glass thermal breakage, surface temperatures, incident heat flux and failure characteristics. The glass fracture and pyrolysis of the internal thermoplastic materials were observed under thermal radiation. The average breakage time of glass in PV panels showed an increasing trend with increasing inclination of the PV panels. Moreover, when the PV panels were tilted beyond 30°, the time to failure increased more significantly. The maximum temperature difference and heat flux that the PV panels can withstand were primarily measured within the range of 61–84 °C and 8–15 kW/m<sup>2</sup>, respectively. Finally, the test results were simulated by a finite element method (FEM) model, calculating the heat transfer and thermal stress of PV panels: the average errors concerning temperature distributions and failure times were smaller than 15 % compared with the experimental results.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109489"},"PeriodicalIF":4.9,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142539307","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 : 2024-10-23DOI: 10.1016/j.ijthermalsci.2024.109493
Domala Sai Suhas, Vikrant Khullar
Engineering efficient optical charging process necessitates efficient photo-thermal energy conversion, transfer, as well as storage of the incident solar radiant energy. The present work is a determining step in deciphering, quantifying, and understanding the aforementioned steps involved in the optical charging of PCMs. Herein, the effect of particle size, concentration and thermochromism have been critically investigated. In particular, detailed optical characterization and photo-thermal experimentation pertinent to non-thermochromic nanoparticles laden PCM (referred to as NP-PCM) and thermochromic micro capsules laden PCM (referred to as TMCP-PCM) has been undertaken. Detailed optical analysis points out that opposed to NP-PCM, TMCP-PCM significantly scatter the incident radiations – the diffuse transmittance (at room temperature) in the two cases being approximately 2 % and 39 % respectively. Furthermore, whereas, optical properties of non-thermochromic nanoparticles are nearly invariant to temperature changes; in the case of thermochromic microcapsules, the magnitude of scattering further increases and diffuse transmittance reaches as high as 51 % at elevated temperatures. Although, thermochromism helps in enhancing the penetration depth at elevated temperatures, but, due to significant fraction of scattering, the photo-thermal energy conversion is not that effective. In terms of temperature field, spatial-temporal temperature distribution curves reveal that temperature spread (in the liquid phase) in case of optical charging of non-thermochromic particles (carbon soot nanoparticles) laden PCMs is significantly high (as high as approximately 24 °C) relative to that observed in case of thermochromic particles (microcapsules) laden PCMs (approximately, 4 °C). The magnitude of the temperature spread (being representative of the deviation from thermostatic optical charging) clearly points out that opposed to non-thermochromic laden PCMs, nearly thermostatic optical charging can be achieved in case of thermochromic particles laden PCMs.
Furthermore, in case of optical charging without thermochromic assistance, the temperature spread, peak temperatures and the melting rates increase with increase in particles concentration. Whereas, in the latter case, although the temperature spread and peak temperatures are nearly independent; the melting rates do depend on the particles’ concentration. Overall, the present work is a significant step towards accelerated-thermostatic thermal energy storage.
{"title":"Understanding photo-thermal and melting mechanisms in optical charging of nano and micro particles laden organic PCMs","authors":"Domala Sai Suhas, Vikrant Khullar","doi":"10.1016/j.ijthermalsci.2024.109493","DOIUrl":"10.1016/j.ijthermalsci.2024.109493","url":null,"abstract":"<div><div>Engineering efficient optical charging process necessitates efficient photo-thermal energy conversion, transfer, as well as storage of the incident solar radiant energy. The present work is a determining step in deciphering, quantifying, and understanding the aforementioned steps involved in the optical charging of PCMs. Herein, the effect of particle size, concentration and thermochromism have been critically investigated. In particular, detailed optical characterization and photo-thermal experimentation pertinent to non-thermochromic nanoparticles laden PCM (referred to as NP-PCM) and thermochromic micro capsules laden PCM (referred to as TMCP-PCM) has been undertaken. Detailed optical analysis points out that opposed to NP-PCM, TMCP-PCM significantly scatter the incident radiations – the diffuse transmittance (at room temperature) in the two cases being approximately 2 % and 39 % respectively. Furthermore, whereas, optical properties of non-thermochromic nanoparticles are nearly invariant to temperature changes; in the case of thermochromic microcapsules, the magnitude of scattering further increases and diffuse transmittance reaches as high as 51 % at elevated temperatures. Although, thermochromism helps in enhancing the penetration depth at elevated temperatures, but, due to significant fraction of scattering, the photo-thermal energy conversion is not that effective. In terms of temperature field, spatial-temporal temperature distribution curves reveal that temperature spread (in the liquid phase) in case of optical charging of non-thermochromic particles (carbon soot nanoparticles) laden PCMs is significantly high (as high as approximately 24 °C) relative to that observed in case of thermochromic particles (microcapsules) laden PCMs (approximately, 4 °C). The magnitude of the temperature spread (being representative of the deviation from thermostatic optical charging) clearly points out that opposed to non-thermochromic laden PCMs, nearly thermostatic optical charging can be achieved in case of thermochromic particles laden PCMs.</div><div>Furthermore, in case of optical charging without thermochromic assistance, the temperature spread, peak temperatures and the melting rates increase with increase in particles concentration. Whereas, in the latter case, although the temperature spread and peak temperatures are nearly independent; the melting rates do depend on the particles’ concentration. Overall, the present work is a significant step towards accelerated-thermostatic thermal energy storage.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"208 ","pages":"Article 109493"},"PeriodicalIF":4.9,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142539316","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}
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