Pub Date : 2024-11-05DOI: 10.1016/j.ijheatmasstransfer.2024.126327
I.M. Bugarin , T.F. Oliveira
Extending our previous investigations on the motion of a single droplet in confined natural convection flows, the present work describes the influence of droplet motion on heat transfer, considering a binary liquid confined in a square enclosure heated by the side-walls. Our model assumes an incompressible flow of two Newtonian fluids with the same dynamic viscosity, density, and thermal expansion coefficient. Additionally, we assume both fluids to have distinct thermal conductivity and heat capacity coefficients. Considering a Rayleigh number of and a Prandtl number of , we investigated the influence of the droplet position, , on the instantaneous Nusselt number, , for two possible motion patterns: the droplet orbiting within a periodic flow or trapped at the enclosure’s center. Our results indicate that the relative heat capacity of the fluids significantly influences Nusselt when compared with the relative thermal conductivity. We also observed that when trapped at the central region, the droplet causes to decrease by 5%, assuming an almost constant value regardless of both relative thermal properties. However, when orbiting in periodic motion, the droplet caused to oscillate periodically, reaching its maximum value as it moves toward the vicinity of the hot wall. While increasing the relative thermal properties resulted in an enhancement of , the average Nusselt number, , displayed modest variation, while remained the same for all cases. Furthermore, our investigations showed that increased by up to 24.4%, equivalent to doubling the Rayleigh number of the mono-phase flow. Therefore, our results highlight significant heat transfer enhancement potential, paving the way for further investigation in future work.
{"title":"The effect of a single droplet on heat transfer through a square enclosure heated by side-walls","authors":"I.M. Bugarin , T.F. Oliveira","doi":"10.1016/j.ijheatmasstransfer.2024.126327","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126327","url":null,"abstract":"<div><div>Extending our previous investigations on the motion of a single droplet in confined natural convection flows, the present work describes the influence of droplet motion on heat transfer, considering a binary liquid confined in a square enclosure heated by the side-walls. Our model assumes an incompressible flow of two Newtonian fluids with the same dynamic viscosity, density, and thermal expansion coefficient. Additionally, we assume both fluids to have distinct thermal conductivity and heat capacity coefficients. Considering a Rayleigh number of <span><math><mrow><mi>R</mi><mi>a</mi><mo>=</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>4</mn></mrow></msup></mrow></math></span> and a Prandtl number of <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>7</mn><mo>.</mo><mn>0</mn></mrow></math></span>, we investigated the influence of the droplet position, <span><math><msub><mrow><mi>x</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span>, on the instantaneous Nusselt number, <span><math><mrow><mi>N</mi><mi>u</mi></mrow></math></span>, for two possible motion patterns: the droplet orbiting within a periodic flow or trapped at the enclosure’s center. Our results indicate that the relative heat capacity of the fluids significantly influences Nusselt when compared with the relative thermal conductivity. We also observed that when trapped at the central region, the droplet causes <span><math><mrow><mi>N</mi><mi>u</mi></mrow></math></span> to decrease by 5%, assuming an almost constant value regardless of both relative thermal properties. However, when orbiting in periodic motion, the droplet caused <span><math><mrow><mi>N</mi><mi>u</mi></mrow></math></span> to oscillate periodically, reaching its maximum value <span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mtext>max</mtext></mrow></msub></mrow></math></span> as it moves toward the vicinity of the hot wall. While increasing the relative thermal properties resulted in an enhancement of <span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mtext>max</mtext></mrow></msub></mrow></math></span>, the average Nusselt number, <span><math><mover><mrow><mi>N</mi><mi>u</mi></mrow><mo>¯</mo></mover></math></span>, displayed modest variation, while <span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mtext>min</mtext></mrow></msub></mrow></math></span> remained the same for all cases. Furthermore, our investigations showed that <span><math><mrow><mi>N</mi><msub><mrow><mi>u</mi></mrow><mrow><mtext>max</mtext></mrow></msub></mrow></math></span> increased by up to 24.4%, equivalent to doubling the Rayleigh number of the mono-phase flow. Therefore, our results highlight significant heat transfer enhancement potential, paving the way for further investigation in future work.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126327"},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587454","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 : 2024-11-05DOI: 10.1016/j.ijheatmasstransfer.2024.126403
Jiateng Zhao , Haolin Gan , Yucheng Dai , Kaibao Liu , Changhui Liu
The rapid development of electronic devices necessitates reliable thermal control systems for efficient thermal management. The combination of pulsating heat pipes (PHPs) with phase change materials (PCMs) facilitates uniform and efficient thermal regulation. This study presents a novel coupled thermal control module that integrates a three-dimensional arrayed pulsating heat pipe (3D-APHP) with a dual-plane and arrayed structure and solid-solid PCM composites. The heat transfer characteristics of the 3D-APHP, the phase change characteristics of the PCM composites, and the interaction between the 3D-APHP and PCM composites under different heating powers and filling rates were experimentally investigated. The results show that the latent heat absorption properties of the PCM composites significantly reduce the temperature fluctuation range and pulsation amplitude of the 3D-APHP, enhancing the temperature uniformity and lowering the overall temperature of the 3D-APHP by approximately 3–10 °C. The efficient thermal conductivity mechanism of the 3D-APHP ensure that the axial temperature difference of the PCM composites is controlled within 10 °C and the radial temperature difference is controlled within 1.5 °C, effectively promoting uniform heat distribution and enhancing the overall temperature rise rate. Additionally, in passive operating mode, the overall temperature difference of the 3D-APHP is smaller and the heat transfer stability is enhanced; in passive/active coupling operating mode, the average temperature of the evaporation section of the 3D-APHP decreases and the thermal response speed increases. The working characteristics of these two modes can be applied to different scenarios, highlighting the innovative integration of PHPs and PCMs in advanced thermal management solutions.
{"title":"Investigation on the heat transfer characteristics of thermal control system based on phase change material coupled with three-dimensional arrayed pulsating heat pipe","authors":"Jiateng Zhao , Haolin Gan , Yucheng Dai , Kaibao Liu , Changhui Liu","doi":"10.1016/j.ijheatmasstransfer.2024.126403","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126403","url":null,"abstract":"<div><div>The rapid development of electronic devices necessitates reliable thermal control systems for efficient thermal management. The combination of pulsating heat pipes (PHPs) with phase change materials (PCMs) facilitates uniform and efficient thermal regulation. This study presents a novel coupled thermal control module that integrates a three-dimensional arrayed pulsating heat pipe (3D-APHP) with a dual-plane and arrayed structure and solid-solid PCM composites. The heat transfer characteristics of the 3D-APHP, the phase change characteristics of the PCM composites, and the interaction between the 3D-APHP and PCM composites under different heating powers and filling rates were experimentally investigated. The results show that the latent heat absorption properties of the PCM composites significantly reduce the temperature fluctuation range and pulsation amplitude of the 3D-APHP, enhancing the temperature uniformity and lowering the overall temperature of the 3D-APHP by approximately 3–10 °C. The efficient thermal conductivity mechanism of the 3D-APHP ensure that the axial temperature difference of the PCM composites is controlled within 10 °C and the radial temperature difference is controlled within 1.5 °C, effectively promoting uniform heat distribution and enhancing the overall temperature rise rate. Additionally, in passive operating mode, the overall temperature difference of the 3D-APHP is smaller and the heat transfer stability is enhanced; in passive/active coupling operating mode, the average temperature of the evaporation section of the 3D-APHP decreases and the thermal response speed increases. The working characteristics of these two modes can be applied to different scenarios, highlighting the innovative integration of PHPs and PCMs in advanced thermal management solutions.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126403"},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587451","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}
Complete analysis of the dynamic characteristics of the proton exchange membrane electrolytic cell (PEMEC) is significant for its efficient and flexible utilization. To fully reflect the dynamic process including thermo-electric interactions within PEMEC, this paper disassembles this process and simplifies it for representation through a clear diagram of dynamic power flow. On this basis, we proposed a novel combined qualitative and quantitative analytical method for the comprehensive response by defining the evaluating indexes for PEMEC's response performance. Meanwhile, we analyzed the change pattern of dynamic response behavior, response time and the influence of thermo-electric interaction under multi-scenarios, like different voltage abrupt change magnitudes, different cathode operating pressures, and different inlet water temperatures. The results show that the PEMEC has the biggest response behavior with the longest response time under the largest external voltage variation magnitude. Besides, there is the shortest response time and smallest parameters total changes after response when the cathode operating pressure is 15bar Moreover, when the inlet water temperature is 40 °C it has the characteristic of quick action time and small response magnitude. The model, analysis method, and findings in this paper provide an effective reference for the operational regulation of PEMEC's thermal and electrical parameters.
{"title":"Thermo-electric coupling dynamic modeling and response behavior analysis of PEMEC based on heat current method","authors":"Yunxi Yang, Junhong Hao, Jinglong Zhou, Xingce Wang, Yanqiang Kong, Xiaoze Du","doi":"10.1016/j.ijheatmasstransfer.2024.126395","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126395","url":null,"abstract":"<div><div>Complete analysis of the dynamic characteristics of the proton exchange membrane electrolytic cell (PEMEC) is significant for its efficient and flexible utilization. To fully reflect the dynamic process including thermo-electric interactions within PEMEC, this paper disassembles this process and simplifies it for representation through a clear diagram of dynamic power flow. On this basis, we proposed a novel combined qualitative and quantitative analytical method for the comprehensive response by defining the evaluating indexes for PEMEC's response performance. Meanwhile, we analyzed the change pattern of dynamic response behavior, response time and the influence of thermo-electric interaction under multi-scenarios, like different voltage abrupt change magnitudes, different cathode operating pressures, and different inlet water temperatures. The results show that the PEMEC has the biggest response behavior with the longest response time under the largest external voltage variation magnitude. Besides, there is the shortest response time and smallest parameters total changes after response when the cathode operating pressure is 15bar Moreover, when the inlet water temperature is 40 °C it has the characteristic of quick action time and small response magnitude. The model, analysis method, and findings in this paper provide an effective reference for the operational regulation of PEMEC's thermal and electrical parameters.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126395"},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587453","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}
A 3 mm thick loop heat pipe (LHP) charged with ammonia for the heat dissipation under low temperature environment was designed, fabricated, and evaluated experimentally. A thin and flat thermal path, which keeps the temperature of the heat source lower than -25 °C by dissipating 10 W heat load to the heat sink of -35 °C, is required for the imaging sensor for a satellite. In this study, a 3 mm thick loop heat pipe (LHP) charged with ammonia was proposed. The monolithic fabrication by additive manufacturing was utilized for the pressure resistant rib structure for high vapor pressure of ammonia. The LHP satisfying the required thermal performance and pressure resistivity was designed based on the simulation. The condenser of the fabricated LHP was connected to the cold plate, and the basic thermal performance was evaluated in the constant temperature chamber ranging the ambient temperature under the horizontal orientation. Under the ambient temperature of -35 °C, the evaporator temperature was -26.2 °C when 10 W heat load was applied; thus, the requirement was satisfied. The effective thermal conductivity of 6050–7730 W/(m·K) was shown when heat load of 5 to 15 W was applied under the ambient temperature ranging from -45 to 20 °C. The orientation dependence was also investigated under top heat and bottom heat orientation, and the similar performance as the horizontal orientation was observed. A power cycle test under horizontal orientation demonstrated the fast temperature response and hysteresis-free performance; thus, preferable characteristics as a thermal device was exhibited. The experimental results were compared with the simulation and agreed upon the simulation results.
{"title":"Thermal performance of ammonia-based thin flat loop heat pipe fabricated by additive manufacturing","authors":"Makoto Kamata , Kazuki Hayashi , Noriyuki Watanabe , Kazuhiro Nakazawa , Takeshi Tsuru , Yuki Akizuki , Hosei Nagano","doi":"10.1016/j.ijheatmasstransfer.2024.126382","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126382","url":null,"abstract":"<div><div>A 3 mm thick loop heat pipe (LHP) charged with ammonia for the heat dissipation under low temperature environment was designed, fabricated, and evaluated experimentally. A thin and flat thermal path, which keeps the temperature of the heat source lower than -25 °C by dissipating 10 W heat load to the heat sink of -35 °C, is required for the imaging sensor for a satellite. In this study, a 3 mm thick loop heat pipe (LHP) charged with ammonia was proposed. The monolithic fabrication by additive manufacturing was utilized for the pressure resistant rib structure for high vapor pressure of ammonia. The LHP satisfying the required thermal performance and pressure resistivity was designed based on the simulation. The condenser of the fabricated LHP was connected to the cold plate, and the basic thermal performance was evaluated in the constant temperature chamber ranging the ambient temperature under the horizontal orientation. Under the ambient temperature of -35 °C, the evaporator temperature was -26.2 °C when 10 W heat load was applied; thus, the requirement was satisfied. The effective thermal conductivity of 6050–7730 W/(m·K) was shown when heat load of 5 to 15 W was applied under the ambient temperature ranging from -45 to 20 °C. The orientation dependence was also investigated under top heat and bottom heat orientation, and the similar performance as the horizontal orientation was observed. A power cycle test under horizontal orientation demonstrated the fast temperature response and hysteresis-free performance; thus, preferable characteristics as a thermal device was exhibited. The experimental results were compared with the simulation and agreed upon the simulation results.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126382"},"PeriodicalIF":5.0,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142587455","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 : 2024-11-04DOI: 10.1016/j.ijheatmasstransfer.2024.126387
Bolin Hu , Qingguo Lin , Ting Li , Weifeng Li , Haifeng Liu , Fuchen Wang
In this study, the flow behavior and heat transfer characteristics of the liquid film on the hot wall by inclined jet impingement are experimentally studied in detail. The effects of jet parameters, such as jet inclination angle, impingement distance, jet Reynolds number (Rej), and nozzle diameter are explored. The liquid film flow is visualized using a high-speed camera, and the surface temperature and heat flux are obtained by solving the inverse heat conduction problem. The results indicate that the liquid film shape is strongly affected by jet inclination angle but is almost unaffected by other parameters. As the inclination angle increases, the liquid film shape changes from elliptical to fusiform. In addition, the onset, enhancement, and disappearance of boiling cause the expansion and contraction of liquid film. The splashing rate is barely affected by jet parameters and remains within the range of 80–95 % under all conditions. The propagation of wetting fronts exhibits anisotropy. Except for the impingement distance, the position of wetting fronts along y-axis direction displays a high dependence on all parameters. The Rej and nozzle diameter have a significant effect on the heat flux at the impingement point and parallel flow zone, while the jet inclination angle and impingement distance only effect the impingement point. The visualization image proves that the droplet impingement pattern is the main reason for the increase in heat flux at higher impingement distances. Optimizing jet parameters can promote the wall to enter the rapid cooling stage in advance and increase maximum heat flux, thereby improving the maximum cooling capacity of the jet. Finally, an empirical equation is proposed to predict the maximum Nusselt number.
本研究通过实验详细研究了倾斜射流撞击热壁上液膜的流动行为和传热特性。研究探讨了射流参数（如射流倾角、撞击距离、射流雷诺数 (Rej) 和喷嘴直径）的影响。使用高速摄像机对液膜流动进行了观察，并通过求解逆热传导问题获得了表面温度和热通量。结果表明，液膜形状受喷射倾角的影响很大，但几乎不受其他参数的影响。随着倾角的增大，液膜形状从椭圆形变为纺锤形。此外，沸腾的开始、增强和消失也会导致液膜的膨胀和收缩。飞溅率几乎不受喷射参数的影响，在所有条件下都保持在 80-95 % 的范围内。润湿前沿的传播呈现各向异性。除撞击距离外，润湿前沿 Y 轴方向的位置与所有参数都有很大关系。Rej 和喷嘴直径对撞击点和平行流区的热通量有显著影响，而射流倾角和撞击距离仅对撞击点有影响。可视化图像证明，液滴撞击模式是撞击距离越远热通量越高的主要原因。优化射流参数可以促进壁面提前进入快速冷却阶段，增加最大热通量，从而提高射流的最大冷却能力。最后，提出了预测最大努塞尔特数的经验方程。
{"title":"Flow behavior and heat transfer characteristics of liquid film on vertical hot surface by inclined jet impingement","authors":"Bolin Hu , Qingguo Lin , Ting Li , Weifeng Li , Haifeng Liu , Fuchen Wang","doi":"10.1016/j.ijheatmasstransfer.2024.126387","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126387","url":null,"abstract":"<div><div>In this study, the flow behavior and heat transfer characteristics of the liquid film on the hot wall by inclined jet impingement are experimentally studied in detail. The effects of jet parameters, such as jet inclination angle, impingement distance, jet Reynolds number (<em>Re</em><sub>j</sub>), and nozzle diameter are explored. The liquid film flow is visualized using a high-speed camera, and the surface temperature and heat flux are obtained by solving the inverse heat conduction problem. The results indicate that the liquid film shape is strongly affected by jet inclination angle but is almost unaffected by other parameters. As the inclination angle increases, the liquid film shape changes from elliptical to fusiform. In addition, the onset, enhancement, and disappearance of boiling cause the expansion and contraction of liquid film. The splashing rate is barely affected by jet parameters and remains within the range of 80–95 % under all conditions. The propagation of wetting fronts exhibits anisotropy. Except for the impingement distance, the position of wetting fronts along <em>y</em>-axis direction displays a high dependence on all parameters. The <em>Re</em><sub>j</sub> and nozzle diameter have a significant effect on the heat flux at the impingement point and parallel flow zone, while the jet inclination angle and impingement distance only effect the impingement point. The visualization image proves that the droplet impingement pattern is the main reason for the increase in heat flux at higher impingement distances. Optimizing jet parameters can promote the wall to enter the rapid cooling stage in advance and increase maximum heat flux, thereby improving the maximum cooling capacity of the jet. Finally, an empirical equation is proposed to predict the maximum Nusselt number.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126387"},"PeriodicalIF":5.0,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578536","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 : 2024-11-04DOI: 10.1016/j.ijheatmasstransfer.2024.126397
Li-Tao Yang , Shao-Fei Zheng , Ruo-Tong Wang , Kai Chen , Yi-Feng Wang , Yan-Ru Yang , Duu-Jong Lee , Xiao-Dong Wang
In this work, the effect of internal convection on the heat transport of condensing droplets is theoretically and numerically focused on considering two typical working scenes (pure steam and moist air). A three-dimensional transient multiphysics model is first constructed by elaborately coupling time-dependent multiple physics during the dynamic growth of condensing droplets. Considering variable surface wettability and industrially universal applications, heat transport characteristics of condensing droplets in these two scenes are comparatively analyzed over a wide range of the droplet radius (500–1000 μm), contact angle (60–120°), and subcooling (1–50 K). It is found that internal convection resulting from the thermocapillary effect and curved vapor/liquid interface plays a progressively prominent role as the contact angle and subcooling increase, accordingly dominating heat transport within droplets. In the steam scene, internal convection is activated neighboring the triple-phase contact line at which the temperature gradient exists solely. In comparison, in the air case, the external vapor diffusion promotes a non-uniform temperature profile over the droplet surface, and the temperature gradient is extended toward the whole surface with stronger internal convection and heat transport enhancement. In general, the quantitative analysis demonstrates that driven by strong internal convection, the total heat flow rate through the droplet can be increased by several times for both two scenes. Furthermore, using the fundamental dimensionless groups governing internal convection, we put forward an empirical correlation of the droplet Nusselt number in two condensing scenes over wide working conditions.
{"title":"The enhancement effects of internal convection on the heat transport of condensing droplets out of pure steam and moist air","authors":"Li-Tao Yang , Shao-Fei Zheng , Ruo-Tong Wang , Kai Chen , Yi-Feng Wang , Yan-Ru Yang , Duu-Jong Lee , Xiao-Dong Wang","doi":"10.1016/j.ijheatmasstransfer.2024.126397","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126397","url":null,"abstract":"<div><div>In this work, the effect of internal convection on the heat transport of condensing droplets is theoretically and numerically focused on considering two typical working scenes (pure steam and moist air). A three-dimensional transient multiphysics model is first constructed by elaborately coupling time-dependent multiple physics during the dynamic growth of condensing droplets. Considering variable surface wettability and industrially universal applications, heat transport characteristics of condensing droplets in these two scenes are comparatively analyzed over a wide range of the droplet radius (500–1000 μm), contact angle (60–120°), and subcooling (1–50 K). It is found that internal convection resulting from the thermocapillary effect and curved vapor/liquid interface plays a progressively prominent role as the contact angle and subcooling increase, accordingly dominating heat transport within droplets. In the steam scene, internal convection is activated neighboring the triple-phase contact line at which the temperature gradient exists solely. In comparison, in the air case, the external vapor diffusion promotes a non-uniform temperature profile over the droplet surface, and the temperature gradient is extended toward the whole surface with stronger internal convection and heat transport enhancement. In general, the quantitative analysis demonstrates that driven by strong internal convection, the total heat flow rate through the droplet can be increased by several times for both two scenes. Furthermore, using the fundamental dimensionless groups governing internal convection, we put forward an empirical correlation of the droplet Nusselt number in two condensing scenes over wide working conditions.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126397"},"PeriodicalIF":5.0,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578679","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 : 2024-11-04DOI: 10.1016/j.ijheatmasstransfer.2024.126399
Wenlong Yang , Haiyan Zhang , Junjie Yang , Jian Qu
Supercritical CO2 (sCO2) is deemed the potential working medium for thermodynamic cycles in the next generation of power machinery. In this paper, the flow and heat transfer characteristics of highly buoyant turbulent sCO2 in horizontal tubes are numerical studied under the non-uniform heating conditions. The tube with a typical internal diameter of 10 mm is selected with mass flux equaling to 300 kg/(m2·s), effective heat fluxes ranging from 20 to 60 kW/m2, and pressure equaling to 8 MPa. The results confirmed that the heat transfer of sCO2 inside the horizontal tube in the circumferential or axial non-uniform heating conditions is greatly deteriorated by 13 %-68 % compared to the uniform heating. The overall heat transfer performance of semi-circumferential axial non-uniform heating is about 2.5 % higher than that of bottom semi-circumferential uniform heating, while the axial temperature difference of the bottom surface exceeds 150 K. Screening three representative heating positions, the bottom heating has the best temperature uniformity. The corresponding turbulent streamlines featured by unique helical structures can substantially improve the circumferential and radial heat transfer over 10 %, enhancing the heat transfer performance of the smooth tube close to that of rifled tubes. Based on the numerical data, viable correlations were developed for calculating the axial local Nusselt number of forced convection heat transfer of sCO2 in horizontal tubes considering the effects of cross-sectional vorticity, secondary flow intensity, and buoyancy-natural convection, and the prediction values are in good agreement with experimental data.
{"title":"Numerical study on fluid flow and heat transfer characteristics of supercritical CO2 in horizontal tube under various non-uniform heating conditions","authors":"Wenlong Yang , Haiyan Zhang , Junjie Yang , Jian Qu","doi":"10.1016/j.ijheatmasstransfer.2024.126399","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126399","url":null,"abstract":"<div><div>Supercritical CO<sub>2</sub> (sCO<sub>2</sub>) is deemed the potential working medium for thermodynamic cycles in the next generation of power machinery. In this paper, the flow and heat transfer characteristics of highly buoyant turbulent sCO<sub>2</sub> in horizontal tubes are numerical studied under the non-uniform heating conditions. The tube with a typical internal diameter of 10 mm is selected with mass flux equaling to 300 kg/(m<sup>2</sup>·s), effective heat fluxes ranging from 20 to 60 kW/m<sup>2</sup>, and pressure equaling to 8 MPa. The results confirmed that the heat transfer of sCO<sub>2</sub> inside the horizontal tube in the circumferential or axial non-uniform heating conditions is greatly deteriorated by 13 %-68 % compared to the uniform heating. The overall heat transfer performance of semi-circumferential axial non-uniform heating is about 2.5 % higher than that of bottom semi-circumferential uniform heating, while the axial temperature difference of the bottom surface exceeds 150 K. Screening three representative heating positions, the bottom heating has the best temperature uniformity. The corresponding turbulent streamlines featured by unique helical structures can substantially improve the circumferential and radial heat transfer over 10 %, enhancing the heat transfer performance of the smooth tube close to that of rifled tubes. Based on the numerical data, viable correlations were developed for calculating the axial local Nusselt number of forced convection heat transfer of sCO<sub>2</sub> in horizontal tubes considering the effects of cross-sectional vorticity, secondary flow intensity, and buoyancy-natural convection, and the prediction values are in good agreement with experimental data.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126399"},"PeriodicalIF":5.0,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578677","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 : 2024-11-04DOI: 10.1016/j.ijheatmasstransfer.2024.126383
Zhe Huang, Xin Shen, Hua Ouyang, Zhaohui Du
During near critical operation, the non-equilibrium phase transition risk of supercritical carbon dioxide compressors usually poses significant challenges to the stability of the whole system. Analyzing the condensation characteristics in the Laval nozzle is considered an effective and feasible method for understanding condensation behavoir of supercritical carbon dioxide in rotating machinery due to the similarity and measurability of flow. In this paper, the Euler-Euler Source numerical model coupled with high-accuracy carbon dioxide real gas property table is established for transonic compressible flow in the Laval nozzle. The non-equilibrium effects of expansion and condensation during transonic flow in the nozzle are discussed and the relationships between inlet parameters, droplet distribution and nucleation rates are also analyzed. The numerical result shows that the non-equilibrium characteristic during the expansion process causes the delay of condensation in the nozzle, resulting in an overestimation of the prediction of carbon dioxide condensation region based on the homogeneous equilibrium model. Shock wave of transonic flow further amplifies the deviation of results and leads to over 12 % overestimation of liquid mass fraction. Increasing the inlet pressure and decreasing the inlet temperature can cause the forward movement of the condensation onset and the reduce of the nucleation region. For supercritical carbon dioxide in the transonic flow, the value of critical pressure ratio can be taken as 0.54∼0.55. These results provide valuable suggestions in the analysis of non-equilibrium condensing flow and designing inlet conditions for experiments.
{"title":"Analysis of non-equilibrium condensation characteristics of supercritical carbon dioxide during transcritical flow in the Laval nozzle","authors":"Zhe Huang, Xin Shen, Hua Ouyang, Zhaohui Du","doi":"10.1016/j.ijheatmasstransfer.2024.126383","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126383","url":null,"abstract":"<div><div>During near critical operation, the non-equilibrium phase transition risk of supercritical carbon dioxide compressors usually poses significant challenges to the stability of the whole system. Analyzing the condensation characteristics in the Laval nozzle is considered an effective and feasible method for understanding condensation behavoir of supercritical carbon dioxide in rotating machinery due to the similarity and measurability of flow. In this paper, the Euler-Euler Source numerical model coupled with high-accuracy carbon dioxide real gas property table is established for transonic compressible flow in the Laval nozzle. The non-equilibrium effects of expansion and condensation during transonic flow in the nozzle are discussed and the relationships between inlet parameters, droplet distribution and nucleation rates are also analyzed. The numerical result shows that the non-equilibrium characteristic during the expansion process causes the delay of condensation in the nozzle, resulting in an overestimation of the prediction of carbon dioxide condensation region based on the homogeneous equilibrium model. Shock wave of transonic flow further amplifies the deviation of results and leads to over 12 % overestimation of liquid mass fraction. Increasing the inlet pressure and decreasing the inlet temperature can cause the forward movement of the condensation onset and the reduce of the nucleation region. For supercritical carbon dioxide in the transonic flow, the value of critical pressure ratio can be taken as 0.54∼0.55. These results provide valuable suggestions in the analysis of non-equilibrium condensing flow and designing inlet conditions for experiments.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126383"},"PeriodicalIF":5.0,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578582","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 : 2024-11-04DOI: 10.1016/j.ijheatmasstransfer.2024.126362
Yu Shi, Xin-Lin Xia, Chuang Sun, Xue Chen
Accurately obtaining the radiation properties of insulating ceramic materials is essential for engineering applications. This article obtained the bidirectional transmittance and reflectance of thermal insulation ceramics, and introduced a new scattering phase function to establish a radiation transfer model based on Monte Carlo method. Combined with parallel genetic algorithm inversion, radiation properties such as extinction coefficient, scattering albedo, and scattering phase function are obtained. Firstly, the experimental optical path is simulated and analyzed, which has little effect on the measurement results due to slight deflection of strong extinction material samples and detectors. For the measurement of bidirectional transmittance, a larger spot radius and detector radius will increase the measurement bidirectional transmittance. Secondly, through parallel genetic algorithm inversion, >5 measurement points are required to obtain their radiative properties, however, the radiation properties of backscattering materials cannot be precisely obtained using bidirectional transmittance for inversion. The required inversion accuracy can be achieved when the bidirectional transmittance and reflectance ratio measurement angle step is <4 °. Finally, this study determined the radiation properties of ceramic insulating materials that show little wavelength variation, their spectral extinction coefficients are above 9000m−1, and spectral scattering albedo are greater than 0.9. It is difficult to characterize scattering features using isotropic scattering phase functions because materials have both forward and backward scattering characteristics. The scattering characteristics of insulation ceramics described using the newly proposed scattering phase function have higher accuracy.
{"title":"Acquisition and reconstruction of scattering characteristics of thermal insulation ceramics","authors":"Yu Shi, Xin-Lin Xia, Chuang Sun, Xue Chen","doi":"10.1016/j.ijheatmasstransfer.2024.126362","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126362","url":null,"abstract":"<div><div>Accurately obtaining the radiation properties of insulating ceramic materials is essential for engineering applications. This article obtained the bidirectional transmittance and reflectance of thermal insulation ceramics, and introduced a new scattering phase function to establish a radiation transfer model based on Monte Carlo method. Combined with parallel genetic algorithm inversion, radiation properties such as extinction coefficient, scattering albedo, and scattering phase function are obtained. Firstly, the experimental optical path is simulated and analyzed, which has little effect on the measurement results due to slight deflection of strong extinction material samples and detectors. For the measurement of bidirectional transmittance, a larger spot radius and detector radius will increase the measurement bidirectional transmittance. Secondly, through parallel genetic algorithm inversion, >5 measurement points are required to obtain their radiative properties, however, the radiation properties of backscattering materials cannot be precisely obtained using bidirectional transmittance for inversion. The required inversion accuracy can be achieved when the bidirectional transmittance and reflectance ratio measurement angle step is <4 °. Finally, this study determined the radiation properties of ceramic insulating materials that show little wavelength variation, their spectral extinction coefficients are above 9000m<sup>−1</sup>, and spectral scattering albedo are greater than 0.9. It is difficult to characterize scattering features using isotropic scattering phase functions because materials have both forward and backward scattering characteristics. The scattering characteristics of insulation ceramics described using the newly proposed scattering phase function have higher accuracy.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126362"},"PeriodicalIF":5.0,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578580","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 : 2024-11-04DOI: 10.1016/j.ijheatmasstransfer.2024.126402
Xin Yan , Yue Wu , Zitao Zhang , Kailu Cui , Haoteng Zhao , Kun He
The flow boiling heat transfer in the RRM (i.e. ribbed micro-channel with aligned side-wall rectangular cavities), ORM (i.e. ribbed micro-channel with offset side-wall rectangular cavities), and ORMB (i.e. ribbed micro-channel with offset side-wall and bottom rectangular cavities) were experimentally investigated at a range of heat fluxes and mass fluxes. Combined with the visualization technology, the influences of offset rectangular cavities on the heat transfer and pressure drop penalty were revealed. The results showed that the existence of offset rectangular cavities enhances the heat transfer performance of micro-channels in both single-phase and two-phase regions. The bottom rectangular cavities in the ORMB enhances the disturbance to the main stream, thus further enhancing the heat transfer performance in the single-phase region and shifting from laminar to transitional flow earlier compared to the ORM. The capillary effect provided by the bottom cavities intensifies the heat transfer in the two-phase region, resulting in a significant increase in the critical heat flux in the ORMB. Compared to the ORM, the maximum increase of critical heat flux in the ORMB reaches 22.3 % (17.57 W·cm−2). The existence of offset rectangular cavities causes alternating resistance forces to the main stream, which increases the pressure drop in the ORM by 8–32.2 % compared to the RRM. The capillary effect provided by the bottom cavities to the liquid-phase in the ORMB is beneficial for the alleviation of vapor blockage and expansion. Hence the pressure drop in the ORMB is reduced by 82.3 % at most compared to the ORM in the two-phase region.
{"title":"Experimental study of flow boiling heat transfer in rectangular ribbed micro-channels with rectangular cavities","authors":"Xin Yan , Yue Wu , Zitao Zhang , Kailu Cui , Haoteng Zhao , Kun He","doi":"10.1016/j.ijheatmasstransfer.2024.126402","DOIUrl":"10.1016/j.ijheatmasstransfer.2024.126402","url":null,"abstract":"<div><div>The flow boiling heat transfer in the RRM (i.e. ribbed micro-channel with aligned side-wall rectangular cavities), ORM (i.e. ribbed micro-channel with offset side-wall rectangular cavities), and ORMB (i.e. ribbed micro-channel with offset side-wall and bottom rectangular cavities) were experimentally investigated at a range of heat fluxes and mass fluxes. Combined with the visualization technology, the influences of offset rectangular cavities on the heat transfer and pressure drop penalty were revealed. The results showed that the existence of offset rectangular cavities enhances the heat transfer performance of micro-channels in both single-phase and two-phase regions. The bottom rectangular cavities in the ORMB enhances the disturbance to the main stream, thus further enhancing the heat transfer performance in the single-phase region and shifting from laminar to transitional flow earlier compared to the ORM. The capillary effect provided by the bottom cavities intensifies the heat transfer in the two-phase region, resulting in a significant increase in the critical heat flux in the ORMB. Compared to the ORM, the maximum increase of critical heat flux in the ORMB reaches 22.3 % (17.57 W·cm<sup>−2</sup>). The existence of offset rectangular cavities causes alternating resistance forces to the main stream, which increases the pressure drop in the ORM by 8–32.2 % compared to the RRM. The capillary effect provided by the bottom cavities to the liquid-phase in the ORMB is beneficial for the alleviation of vapor blockage and expansion. Hence the pressure drop in the ORMB is reduced by 82.3 % at most compared to the ORM in the two-phase region.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"236 ","pages":"Article 126402"},"PeriodicalIF":5.0,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578581","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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