International Journal of Thermal Sciences最新文献_第5页

Design of a high-accuracy air temperature measurement system using computational fluid dynamics and neural networks

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-23 DOI: 10.1016/j.ijthermalsci.2025.109895

Jie Yang , Jiale Jiang , Renhui Ding , Qingquan Liu

Global temperatures are rising by approximately 0.1 °C per decade. Existing air temperature measurement systems often report temperatures higher than actual air temperature due to the effects of solar radiation, leading to errors of up to 1 °C. As a result, there is an urgent need for a new temperature measurement system with improved radiation protection and ventilation capabilities. Furthermore, a specialized temperature error correction model is essential for the new system. Computational fluid dynamics (CFD) software was employed to simulate the radiation shielding and ventilation performance of the new system. Temperature differences between the new system and actual air temperature under various environmental conditions were quantified using CFD software. Subsequently, a specialized temperature difference correction model, incorporating multiple environmental variables, was developed using a neural network algorithm. Finally, the measurement accuracy of the new system was evaluated through field comparison experiments. During the experiments, a 076B fan aspirated temperature measurement system with an error of less than 0.03 °C served as the reference system. Before correction, the new system exhibited a maximum temperature difference of 0.69 °C and an average temperature difference of 0.35 °C compared to the reference system. The mean absolute error, root mean square error, and correlation coefficient between the temperature differences from the correction model and the experimental data were 0.07 °C, 0.08 °C, and 0.9 °C, respectively. After correction, the average temperature difference decreased to 0.06 °C. These results indicate that the new system has significant potential for high-accuracy temperature measurement.

{"title":"Design of a high-accuracy air temperature measurement system using computational fluid dynamics and neural networks","authors":"Jie Yang , Jiale Jiang , Renhui Ding , Qingquan Liu","doi":"10.1016/j.ijthermalsci.2025.109895","DOIUrl":"10.1016/j.ijthermalsci.2025.109895","url":null,"abstract":"<div><div>Global temperatures are rising by approximately 0.1 °C per decade. Existing air temperature measurement systems often report temperatures higher than actual air temperature due to the effects of solar radiation, leading to errors of up to 1 °C. As a result, there is an urgent need for a new temperature measurement system with improved radiation protection and ventilation capabilities. Furthermore, a specialized temperature error correction model is essential for the new system. Computational fluid dynamics (CFD) software was employed to simulate the radiation shielding and ventilation performance of the new system. Temperature differences between the new system and actual air temperature under various environmental conditions were quantified using CFD software. Subsequently, a specialized temperature difference correction model, incorporating multiple environmental variables, was developed using a neural network algorithm. Finally, the measurement accuracy of the new system was evaluated through field comparison experiments. During the experiments, a 076B fan aspirated temperature measurement system with an error of less than 0.03 °C served as the reference system. Before correction, the new system exhibited a maximum temperature difference of 0.69 °C and an average temperature difference of 0.35 °C compared to the reference system. The mean absolute error, root mean square error, and correlation coefficient between the temperature differences from the correction model and the experimental data were 0.07 °C, 0.08 °C, and 0.9 °C, respectively. After correction, the average temperature difference decreased to 0.06 °C. These results indicate that the new system has significant potential for high-accuracy temperature measurement.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109895"},"PeriodicalIF":4.9,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143685497","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}

引用次数: 0

Large eddy simulation on thermal striping of liquid lead-bismuth eutectic in parallel five-jet

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-22 DOI: 10.1016/j.ijthermalsci.2025.109870

Wen-De Zhao , Hong-Na Zhang , Xiao-Bin Li , Jun-Liang Guo , Yue Wang , Wei-Hua Cai , Shu-Qi Meng , Fang Chen , Yu-Long Mao , Feng-Chen Li

Thermal striping in the upper plenum of the lead-cooled fast reactor (LFR) is a temperature fluctuation phenomenon caused by the mixing of two non-isothermal fluids, and can lead to high cycle thermal fatigue and cracks in adjacent structures. Quantitative study of thermal striping is of great significance for the safe operation of reactors. This paper studies the thermal striping phenomena of lead-bismuth eutectic in a parallel five-jet plenum based on large eddy simulation. The parametric effects on characteristics of temperature fluctuation in terms of its statistics and flow structures are focused on, including the effects of temperature differences and velocity ratios. The results show that the temperature difference and velocity ratio significantly affect the flow patterns of thermal and flow fields, as well as the statistical characteristics of thermal striping. Under isovelocity conditions, the flow pattern of fluids is symmetric, whereas it is affected by velocity ratio in non-isovelocity scenarios. With isovelocity, increasing temperature difference raises the average temperature, heat flux and temperature fluctuation intensity. For non-isovelocity conditions, higher velocity ratios reduce average temperature but increase heat flux, with temperature fluctuation intensity showing an initial increase followed by a decrease. Spectral analysis indicates that the temperature difference primarily increases the temperature fluctuation amplitudes (the dominant frequency stabilized at about 5 Hz). Conversely, increasing velocity ratio decreases the amplitude and raises the dominant frequency. These findings provide valuable insights for understanding the mechanism of thermal striping of liquid lead-bismuth eutectic.

{"title":"Large eddy simulation on thermal striping of liquid lead-bismuth eutectic in parallel five-jet","authors":"Wen-De Zhao , Hong-Na Zhang , Xiao-Bin Li , Jun-Liang Guo , Yue Wang , Wei-Hua Cai , Shu-Qi Meng , Fang Chen , Yu-Long Mao , Feng-Chen Li","doi":"10.1016/j.ijthermalsci.2025.109870","DOIUrl":"10.1016/j.ijthermalsci.2025.109870","url":null,"abstract":"<div><div>Thermal striping in the upper plenum of the lead-cooled fast reactor (LFR) is a temperature fluctuation phenomenon caused by the mixing of two non-isothermal fluids, and can lead to high cycle thermal fatigue and cracks in adjacent structures. Quantitative study of thermal striping is of great significance for the safe operation of reactors. This paper studies the thermal striping phenomena of lead-bismuth eutectic in a parallel five-jet plenum based on large eddy simulation. The parametric effects on characteristics of temperature fluctuation in terms of its statistics and flow structures are focused on, including the effects of temperature differences and velocity ratios. The results show that the temperature difference and velocity ratio significantly affect the flow patterns of thermal and flow fields, as well as the statistical characteristics of thermal striping. Under isovelocity conditions, the flow pattern of fluids is symmetric, whereas it is affected by velocity ratio in non-isovelocity scenarios. With isovelocity, increasing temperature difference raises the average temperature, heat flux and temperature fluctuation intensity. For non-isovelocity conditions, higher velocity ratios reduce average temperature but increase heat flux, with temperature fluctuation intensity showing an initial increase followed by a decrease. Spectral analysis indicates that the temperature difference primarily increases the temperature fluctuation amplitudes (the dominant frequency stabilized at about 5 Hz). Conversely, increasing velocity ratio decreases the amplitude and raises the dominant frequency. These findings provide valuable insights for understanding the mechanism of thermal striping of liquid lead-bismuth eutectic.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109870"},"PeriodicalIF":4.9,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143685494","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}

引用次数: 0

Smoldering fire potential in activated carbons based on surface temperature and carbon monoxide emission

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-22 DOI: 10.1016/j.ijthermalsci.2025.109877

Yejin Ha , Joonho Jeon

Activated carbon has a large surface area and high porosity, which makes it an excellent adsorbent for the removal of industrial pollutants. However, it is associated with significant fire risk including smoldering and auto-ignition because adsorption is an exothermic reaction. Although smoldering is a slow, low-temperature combustion mode, it produces large amounts of toxic gases and can transition into flaming combustion. Therefore, elucidating the combustion characteristics of smoldering activated carbon is important for ensuring fire safety in industrial settings. In this study, the combustion characteristics of activated carbons with different types were investigated under several external heat fluxes. The onset of smoldering was determined based on its characteristic temperature obtained from thermogravimetric analysis. The reaction progression and combustion stages were presented in terms of surface temperature distributions and carbon monoxide emissions during thermal reactions. Additionally, the effects of changes in the exposed surface area and thickness on the combustion behavior of activated carbon were analyzed. Finally, the potential for flame occurrence via the gas-phase reaction during smoldering was examined.

{"title":"Smoldering fire potential in activated carbons based on surface temperature and carbon monoxide emission","authors":"Yejin Ha , Joonho Jeon","doi":"10.1016/j.ijthermalsci.2025.109877","DOIUrl":"10.1016/j.ijthermalsci.2025.109877","url":null,"abstract":"<div><div>Activated carbon has a large surface area and high porosity, which makes it an excellent adsorbent for the removal of industrial pollutants. However, it is associated with significant fire risk including smoldering and auto-ignition because adsorption is an exothermic reaction. Although smoldering is a slow, low-temperature combustion mode, it produces large amounts of toxic gases and can transition into flaming combustion. Therefore, elucidating the combustion characteristics of smoldering activated carbon is important for ensuring fire safety in industrial settings. In this study, the combustion characteristics of activated carbons with different types were investigated under several external heat fluxes. The onset of smoldering was determined based on its characteristic temperature obtained from thermogravimetric analysis. The reaction progression and combustion stages were presented in terms of surface temperature distributions and carbon monoxide emissions during thermal reactions. Additionally, the effects of changes in the exposed surface area and thickness on the combustion behavior of activated carbon were analyzed. Finally, the potential for flame occurrence via the gas-phase reaction during smoldering was examined.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109877"},"PeriodicalIF":4.9,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143685495","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}

引用次数: 0

Exploration of PCM melting in a heated enclosure with vertical plate fins: Experimental analysis

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-21 DOI: 10.1016/j.ijthermalsci.2025.109884

A. Ali Rabienataj Darzi , S. Morteza Mousavi

This study investigates the enhancement of thermal performance in phase change materials (PCMs) through the application of fins. PCMs are renowned for their ability to store energy with minimal temperature fluctuations, rendering them valuable in thermal energy storage systems. However, their low thermal conductivity constrains heat transfer efficiency. By increasing the surface area, fins can enhance convective heat transfer and offer a solution to this limitation. The research conducts experimental analyses on the efficacy of vertical fins within an enclosure heated by a single vertical wall, emphasizing their influence on PCM thermal performance. Melt fronts are monitored at various time intervals, and local temperatures are recorded at nine specific points. The study explores three types of fins: non-perforated fins, circular-perforated fins, and fins with oval cuts. The findings demonstrate a significant improvement in PCM heat transfer rates and thermal behavior with the incorporation of fins, effectively lowering temperatures in proximity to the heat source. Specifically, the inclusion of 1, 3, and 5 non-perforated fins results in reductions of PCM melting times by 13 %, 32 %, and 39 %, respectively. The maximum melting rates for the cases with 5, 3, and 1 non-perforated fins are approximately 133 %, 90 %, and 22 % higher, respectively, compared to the case without fins. Furthermore, the research identifies an efficient fin design with oval cuts, achieving the shortest melting time while remaining cost-effective and lightweight. This indicates that the melting rate in the final stage of the melting process for this design is higher than in the other cases. This design features 30 % less surface area and 40 % less weight than complete fins, making it an attractive option for thermal systems.

{"title":"Exploration of PCM melting in a heated enclosure with vertical plate fins: Experimental analysis","authors":"A. Ali Rabienataj Darzi , S. Morteza Mousavi","doi":"10.1016/j.ijthermalsci.2025.109884","DOIUrl":"10.1016/j.ijthermalsci.2025.109884","url":null,"abstract":"<div><div>This study investigates the enhancement of thermal performance in phase change materials (PCMs) through the application of fins. PCMs are renowned for their ability to store energy with minimal temperature fluctuations, rendering them valuable in thermal energy storage systems. However, their low thermal conductivity constrains heat transfer efficiency. By increasing the surface area, fins can enhance convective heat transfer and offer a solution to this limitation. The research conducts experimental analyses on the efficacy of vertical fins within an enclosure heated by a single vertical wall, emphasizing their influence on PCM thermal performance. Melt fronts are monitored at various time intervals, and local temperatures are recorded at nine specific points. The study explores three types of fins: non-perforated fins, circular-perforated fins, and fins with oval cuts. The findings demonstrate a significant improvement in PCM heat transfer rates and thermal behavior with the incorporation of fins, effectively lowering temperatures in proximity to the heat source. Specifically, the inclusion of 1, 3, and 5 non-perforated fins results in reductions of PCM melting times by 13 %, 32 %, and 39 %, respectively. The maximum melting rates for the cases with 5, 3, and 1 non-perforated fins are approximately 133 %, 90 %, and 22 % higher, respectively, compared to the case without fins. Furthermore, the research identifies an efficient fin design with oval cuts, achieving the shortest melting time while remaining cost-effective and lightweight. This indicates that the melting rate in the final stage of the melting process for this design is higher than in the other cases. This design features 30 % less surface area and 40 % less weight than complete fins, making it an attractive option for thermal systems.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109884"},"PeriodicalIF":4.9,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143685493","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}

引用次数: 0

Modelling the solidification process of supercooled phase change materials with high Prandtl number using the total enthalpy-based lattice Boltzmann method

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-21 DOI: 10.1016/j.ijthermalsci.2025.109881

Baoxin Cao, Guobing Zhou

Modelling the supercooled solidification of PCMs is challenging due to the multi-value problem particularly for high Prandtl numbers (Pr). An improved total enthalpy-based lattice Boltzmann method is applied to simulate the solidification process of supercooled sodium acetate trihydrate (SAT, Pr = 40) in a vertical cylindrical container triggered by local cooling. The evolutions of the SAT temperature profile, solid fraction and particularly the solidification front are monitored, and the effects of the cold source temperature (T_cool) and the cooling area (l × l) are analyzed. The results show that the presented method accurately characterizes the supercooled solidification; decreasing T_cool from −5.5 °C to −7 °C reduces the induction time by 95.7 % and the discharging period by 11.1 %; increasing cooling area l × l from 2 × 2 cm² to 8 × 8 cm² also shortens the induction time from 11 s to 7 s and the discharging period by up to 500 s. The larger cooling area l × l accelerates the movement of the solidification front and also has a significant impact on its morphology. The present model proposes an alternative numerical method for predicting the discharging performance of the supercooled high-Pr PCMs inside containers.

{"title":"Modelling the solidification process of supercooled phase change materials with high Prandtl number using the total enthalpy-based lattice Boltzmann method","authors":"Baoxin Cao, Guobing Zhou","doi":"10.1016/j.ijthermalsci.2025.109881","DOIUrl":"10.1016/j.ijthermalsci.2025.109881","url":null,"abstract":"<div><div>Modelling the supercooled solidification of PCMs is challenging due to the multi-value problem particularly for high Prandtl numbers (<em>Pr</em>). An improved total enthalpy-based lattice Boltzmann method is applied to simulate the solidification process of supercooled sodium acetate trihydrate (SAT, <em>Pr</em> = 40) in a vertical cylindrical container triggered by local cooling. The evolutions of the SAT temperature profile, solid fraction and particularly the solidification front are monitored, and the effects of the cold source temperature (<em>T</em><sub>cool</sub>) and the cooling area (<em>l</em> × <em>l</em>) are analyzed. The results show that the presented method accurately characterizes the supercooled solidification; decreasing <em>T</em><sub>cool</sub> from −5.5 °C to −7 °C reduces the induction time by 95.7 % and the discharging period by 11.1 %; increasing cooling area <em>l</em> × <em>l</em> from 2 × 2 cm<sup>2</sup> to 8 × 8 cm<sup>2</sup> also shortens the induction time from 11 s to 7 s and the discharging period by up to 500 s. The larger cooling area <em>l</em> × <em>l</em> accelerates the movement of the solidification front and also has a significant impact on its morphology. The present model proposes an alternative numerical method for predicting the discharging performance of the supercooled high-<em>Pr</em> PCMs inside containers.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109881"},"PeriodicalIF":4.9,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143685492","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}

引用次数: 0

Thermo-hydraulic performance enhancement in novel secondary connected fractal heat sink with cavities

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-20 DOI: 10.1016/j.ijthermalsci.2025.109855

Shashank Singh, Anup Malik, Harlal Singh Mali

The flexible geometries of microchannel heat sinks (MCHS) allow for modified cooling solutions for a wide range of applications. This adaptability enables heat dissipation enhancement in a variety of sectors, including renewable energy systems and microelectronics. This study aims to build novel MCHS device for thermo-hydraulic performance enhancement. Two devices are, bottom cavities secondary connected fractal heat sink with one branching level (BCSC-FHS-L1) and two branching level (BCSC-FHS-L2), 3D printed by laser powder bed fusion (LPBF) technique. AlSi10Mg alloy is used as solid substrate and water as fluid with single-phase flow. Their performances are studied numerically and validated experimentally using an in-house developed test setup. BCSC-FHS-L2 shows superior thermal performance with the maximum enhancement of 35% in average Nusselt number (

N u_{a v g}

) at Reynolds number (

R e

)=793 with 67% increment in pressure drop (

Δ P

). BCSC-FHS-L2 shows the maximum overall performance (

O P

) at

R e

=270 with 17% enhancement compared to BCSC-FHS-L1 device.

{"title":"Thermo-hydraulic performance enhancement in novel secondary connected fractal heat sink with cavities","authors":"Shashank Singh, Anup Malik, Harlal Singh Mali","doi":"10.1016/j.ijthermalsci.2025.109855","DOIUrl":"10.1016/j.ijthermalsci.2025.109855","url":null,"abstract":"<div><div>The flexible geometries of microchannel heat sinks (MCHS) allow for modified cooling solutions for a wide range of applications. This adaptability enables heat dissipation enhancement in a variety of sectors, including renewable energy systems and microelectronics. This study aims to build novel MCHS device for thermo-hydraulic performance enhancement. Two devices are, bottom cavities secondary connected fractal heat sink with one branching level (BCSC-FHS-L1) and two branching level (BCSC-FHS-L2), 3D printed by laser powder bed fusion (LPBF) technique. AlSi10Mg alloy is used as solid substrate and water as fluid with single-phase flow. Their performances are studied numerically and validated experimentally using an in-house developed test setup. BCSC-FHS-L2 shows superior thermal performance with the maximum enhancement of 35% in average Nusselt number (<span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mi>a</mi><mi>v</mi><mi>g</mi></mrow></msub></mrow></math></span>) at Reynolds number (<span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span>)=793 with 67% increment in pressure drop (<span><math><mrow><mi>Δ</mi><mi>P</mi></mrow></math></span>). BCSC-FHS-L2 shows the maximum overall performance (<span><math><mrow><mi>O</mi><mi>P</mi></mrow></math></span>) at <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span>=270 with 17% enhancement compared to BCSC-FHS-L1 device.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109855"},"PeriodicalIF":4.9,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684993","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}

引用次数: 0

Experimental study of a single-phase immersion cooling system with natural and forced convection

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-20 DOI: 10.1016/j.ijthermalsci.2025.109868

A.S.M. Rokonuzzaman , Kasim Erdem , Bayram Şahin , Mehmed Rafet Özdemir

The rapid advancement of the electronics industry has led to the emergence of miniaturized, high-speed devices with significant amount of volumetric heat generation. Immersion cooling systems offer an effective solution for managing high heat loads, particularly in data centers and battery thermal management systems. However, several fundamental issues of the underlying physical phenomena still need to be addressed to improve the efficiency of these systems. In this study, an immersion cooling system using Novec 7100 dielectric liquid has been experimentally investigated having four electric cartridge heaters with circular and square cross-sections. The effect of distance between heaters on the surface temperature was analyzed under different flow conditions. Furthermore, the effect of heater cross-section on the heat transfer coefficient was examined. For natural convection, the heat transfer coefficient increased as the distance between the heaters was increased for both heaters. As expected, the forced convection mechanism was found to be significantly more effective in heat removal compared to natural convection. At high heat flux values, the heat transfer coefficient was found to be higher for square heaters due to their 1.15 times larger surface area. However, for low heat flux values, the heat transfer coefficient was higher for circular heaters than the square heaters. These findings provide valuable insights into the optimization of immersion cooling systems, highlighting the influence of heater geometry and heater spacing on thermal management efficiency.

{"title":"Experimental study of a single-phase immersion cooling system with natural and forced convection","authors":"A.S.M. Rokonuzzaman , Kasim Erdem , Bayram Şahin , Mehmed Rafet Özdemir","doi":"10.1016/j.ijthermalsci.2025.109868","DOIUrl":"10.1016/j.ijthermalsci.2025.109868","url":null,"abstract":"<div><div>The rapid advancement of the electronics industry has led to the emergence of miniaturized, high-speed devices with significant amount of volumetric heat generation. Immersion cooling systems offer an effective solution for managing high heat loads, particularly in data centers and battery thermal management systems. However, several fundamental issues of the underlying physical phenomena still need to be addressed to improve the efficiency of these systems. In this study, an immersion cooling system using Novec 7100 dielectric liquid has been experimentally investigated having four electric cartridge heaters with circular and square cross-sections. The effect of distance between heaters on the surface temperature was analyzed under different flow conditions. Furthermore, the effect of heater cross-section on the heat transfer coefficient was examined. For natural convection, the heat transfer coefficient increased as the distance between the heaters was increased for both heaters. As expected, the forced convection mechanism was found to be significantly more effective in heat removal compared to natural convection. At high heat flux values, the heat transfer coefficient was found to be higher for square heaters due to their 1.15 times larger surface area. However, for low heat flux values, the heat transfer coefficient was higher for circular heaters than the square heaters. These findings provide valuable insights into the optimization of immersion cooling systems, highlighting the influence of heater geometry and heater spacing on thermal management efficiency.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109868"},"PeriodicalIF":4.9,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143685491","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}

引用次数: 0

Hot surface ignition delay time of ammonia-hydrogen-methane mixtures

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-19 DOI: 10.1016/j.ijthermalsci.2025.109885

Amir Hossein Sharifi Ilkhchi, Amir Mahdi Tahsini

In this research, the effects of adding hydrogen and ammonia to the stoichiometric methane-air mixture, as well as adding ammonia to the stoichiometric hydrogen-air mixture, on ignition delay time changes near a hot surface at two constant temperatures (1400 K and 1600 K) are numerically investigated using a detailed mechanism. The hydrogen-to-methane effectiveness limit (HMEL) is defined in this paper, indicating the point at which the beneficial effect of hydrogen on reducing ignition delay time is reversed, resulting in longer ignition delay times compared to the original mixture, stoichiometric methane-air. Additionally, the hydrogen-to-methane optimal range (HMOR) represents the optimal hydrogen addition range to the stoichiometric methane-air mixture that achieves the lowest ignition delay times. An unpredictable jump in ignition delay time is observed in the methane-hydrogen-air mixture at a hot surface temperature of 1600 K when approximately 14.5 % hydrogen is added. Additionally, adding more than 16 % hydrogen results in longer ignition delay times at higher hot surface temperatures. Conversely, the ignition delay time increases with addition of ammonia in both methane and hydrogen mixtures. Furthermore, it is concluded that adding more than 23–25 % ammonia to the stoichiometric hydrogen-air mixture renders it non-ignitable by a hot surface at 1600 K. This study highlights the impact of hydrogen and ammonia addition on ignition delay time, offering valuable insights for practical applications and providing a foundation for further research on the combustion characteristics of fuels, particularly ammonia and hydrogen.

{"title":"Hot surface ignition delay time of ammonia-hydrogen-methane mixtures","authors":"Amir Hossein Sharifi Ilkhchi, Amir Mahdi Tahsini","doi":"10.1016/j.ijthermalsci.2025.109885","DOIUrl":"10.1016/j.ijthermalsci.2025.109885","url":null,"abstract":"<div><div>In this research, the effects of adding hydrogen and ammonia to the stoichiometric methane-air mixture, as well as adding ammonia to the stoichiometric hydrogen-air mixture, on ignition delay time changes near a hot surface at two constant temperatures (1400 K and 1600 K) are numerically investigated using a detailed mechanism. The hydrogen-to-methane effectiveness limit (HMEL) is defined in this paper, indicating the point at which the beneficial effect of hydrogen on reducing ignition delay time is reversed, resulting in longer ignition delay times compared to the original mixture, stoichiometric methane-air. Additionally, the hydrogen-to-methane optimal range (HMOR) represents the optimal hydrogen addition range to the stoichiometric methane-air mixture that achieves the lowest ignition delay times. An unpredictable jump in ignition delay time is observed in the methane-hydrogen-air mixture at a hot surface temperature of 1600 K when approximately 14.5 % hydrogen is added. Additionally, adding more than 16 % hydrogen results in longer ignition delay times at higher hot surface temperatures. Conversely, the ignition delay time increases with addition of ammonia in both methane and hydrogen mixtures. Furthermore, it is concluded that adding more than 23–25 % ammonia to the stoichiometric hydrogen-air mixture renders it non-ignitable by a hot surface at 1600 K. This study highlights the impact of hydrogen and ammonia addition on ignition delay time, offering valuable insights for practical applications and providing a foundation for further research on the combustion characteristics of fuels, particularly ammonia and hydrogen.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"214 ","pages":"Article 109885"},"PeriodicalIF":4.9,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143645124","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}

引用次数: 0

Balance regulation of heat transfer and flow performances of convective heat exchange of microchannel array structures

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-19 DOI: 10.1016/j.ijthermalsci.2025.109882

Chaomeng Chen, Jie Wang, Liyang Wang, Ping Zhang

As chip integration density increases, the demand for efficient thermal management becomes critical. Traditional microchannel structures often face a trade-off between heat transfer enhancement and increased flow resistance. To address this issue, this study proposes a novel reverse optimization strategy for microchannel array structures, inspired by the natural configurations of leaf veins and spider webs. The optimization process involves two key stages: first, minimizing the maximum thermal resistance of individual microchannel units; second, reducing overall flow resistance through an inverse design approach. The optimized structure is experimentally validated against randomly designed comparative structures. The results demonstrate that the optimized structure achieves a comprehensive performance improvement ranging from 1.54 to 4.47 times over comparative structures. Furthermore, within the scope of this study, the optimized configuration reduces the pressure drop by 23 %–81 % while maintaining high heat transfer efficiency. This research contributes to the development of optimized microchannel array designs for active thermal management systems.

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引用次数: 0

Numerical investigation on thermal insulation effect by coolant layer in performance of transpiration cooling

IF 4.9 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Thermal Sciences

Pub Date : 2025-03-18 DOI: 10.1016/j.ijthermalsci.2025.109856

Yuyang Bian , Xue Liu , Jiayue Zheng , Yanqi Diao , Weixing Zhou , Leonid Yanovskiy

The principle of transpiration cooling involves the internal convective heat transfer within the porous medium and the external thermal insulation by the coolant layer. This work quantitatively analyzed the insulation effect to deeply understand the mechanism of transpiration cooling. The average heat absorption power ratio is 1.12 under the 0.8 % injection ratio, indicating a greater contribution of thermal insulation to the performance of transpiration cooling. An increase in the injection ratio enhances the thermal insulation effect at the end of the porous medium, and the maximum heat absorption power ratio reaches 3.65 at the injection ratio of 0.9 %. Although a change in the mainstream Mach number leads to an overall alteration in the heat absorption power of both aspects, the average heat absorption power ratio of thermal insulation to convective heat transfer improves as the Mach number rises. The thermal insulation effect weakens with an increase in shock wave intensity. An exponential functional relationship exists between the average thermal insulation effect and the wedge angle. Under a wedge angle of 12°, the contribution of thermal insulation is less than that of the convective heat transfer in the porous medium, and the heat absorption power ratio drops to 0.52.

蒸腾冷却的原理包括多孔介质内部的对流传热和冷却剂层的外部隔热。本研究对隔热效果进行了定量分析，以深入了解蒸腾冷却的机理。在 0.8 % 的喷射比下，平均吸热功率比为 1.12，表明隔热对蒸腾冷却性能的贡献更大。喷射比的增加增强了多孔介质末端的隔热效果，在喷射比为 0.9 % 时，最大吸热功率比达到 3.65。虽然主流马赫数的变化会导致两方面吸热功率的整体变化，但隔热与对流传热的平均吸热功率比会随着马赫数的升高而提高。隔热效果随着冲击波强度的增加而减弱。平均隔热效果与楔角之间存在指数函数关系。在楔角为 12° 时，隔热的贡献小于多孔介质中对流传热的贡献，吸热功率比降至 0.52。

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引用次数: 0