Pub Date : 2025-01-15DOI: 10.1016/j.ijthermalsci.2025.109693
Tianyi Wang , Yuepei Cai , Lei Guo , Chuanting Wang , Yuan He , Yong He
Al/PTFE (Aluminum/Polytetrafluoroethylene) is a typical kind of reactive material, which has a variety of potential applications in weapon systems. In this paper, laser ignition experiments were carried out for a pressed and sintered mixture of Al and PTFE powder, and the parameters of Al/PTFE combustion process was measured by infrared thermometer, C-type corundum thermocouple and high-speed camera. The results show that Al particle size and Al content have a significant impact on energy release behavior. As particle size decreases, energy release increases in Al/PTFE specimens with micron-sized Al particles. However, for nano-sized particles, 500 nm particles release more energy than 50 nm particles, likely due to greater oxidation. Besides, increasing Al content enhances the reaction rate of Al/PTFE, but excess Al reduces the energy release. Moreover, in the specimens prepared with mass ratio of 26.5/73.5, self-propagating combustion can be achieved in the specimens with nano Al particles, whereas it fails to occur in the specimens with micron Al particles. And intense chemical reactions were detected in Al/PTFE specimens with smaller particle sizes, with a temperature variation of up to 1763.85 K in 1 s. The highest temperature can reach 2523.45 K. Based on the above experiments, an Al/PTFE laser ignition combustion model was established to characterize the temperature dynamics and combustion mechanisms during the reaction process.
{"title":"Energy release characteristics of Al/PTFE reactive materials under laser ignition experiment","authors":"Tianyi Wang , Yuepei Cai , Lei Guo , Chuanting Wang , Yuan He , Yong He","doi":"10.1016/j.ijthermalsci.2025.109693","DOIUrl":"10.1016/j.ijthermalsci.2025.109693","url":null,"abstract":"<div><div>Al/PTFE (Aluminum/Polytetrafluoroethylene) is a typical kind of reactive material, which has a variety of potential applications in weapon systems. In this paper, laser ignition experiments were carried out for a pressed and sintered mixture of Al and PTFE powder, and the parameters of Al/PTFE combustion process was measured by infrared thermometer, C-type corundum thermocouple and high-speed camera. The results show that Al particle size and Al content have a significant impact on energy release behavior. As particle size decreases, energy release increases in Al/PTFE specimens with micron-sized Al particles. However, for nano-sized particles, 500 nm particles release more energy than 50 nm particles, likely due to greater oxidation. Besides, increasing Al content enhances the reaction rate of Al/PTFE, but excess Al reduces the energy release. Moreover, in the specimens prepared with mass ratio of 26.5/73.5, self-propagating combustion can be achieved in the specimens with nano Al particles, whereas it fails to occur in the specimens with micron Al particles. And intense chemical reactions were detected in Al/PTFE specimens with smaller particle sizes, with a temperature variation of up to 1763.85 K in 1 s. The highest temperature can reach 2523.45 K. Based on the above experiments, an Al/PTFE laser ignition combustion model was established to characterize the temperature dynamics and combustion mechanisms during the reaction process.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109693"},"PeriodicalIF":4.9,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138068","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}
When a hypersonic vehicle is flying at a high Mach number, its leading edge is apt to suffer extremely high heat fluxes induced by aerodynamic heating. The onboard aviation kerosene RP-3 is an excellent coolant to absorb the heat from the heated leading walls. In this work, three new kinds of bionic shaped cooling structures (T-type, Y-type, and H-type channels), are designed for the active cooling of the leading edge, which are compared with traditional parallel cooling structure (P-type), regarding the pressure penalty, maximum temperature, average Nusselt number, overall performance factor, and the cooling efficiency. Meanwhile, different coolant distribution strategies (constant supply, variable supply, and segmented supply strategy) are proposed to deal with the varied aerodynamic heating flux conditions when the hypersonic vehicle undergoes actual flight missions. The results show that the bionic shaped cooling channels have better cooling performances, with the maximum temperature of leading edge reduced by 673 K for the Y-type, 651 K for the T-type, and 525 K for the H-type channels at Re = 892. In addition, the variable supply strategy presents a relatively lower temperature and a more stable temperature variation for both the solid structure and coolant fluid, and so is the most suitable coolant distribution strategy.
{"title":"Numerical analysis on the active cooling characteristics for a hypersonic vehicle leading edge and coolant distribution strategy","authors":"Tingfang Yu , Xing Guo , Jingchun Min , Yicun Tang","doi":"10.1016/j.ijthermalsci.2025.109703","DOIUrl":"10.1016/j.ijthermalsci.2025.109703","url":null,"abstract":"<div><div>When a hypersonic vehicle is flying at a high Mach number, its leading edge is apt to suffer extremely high heat fluxes induced by aerodynamic heating. The onboard aviation kerosene RP-3 is an excellent coolant to absorb the heat from the heated leading walls. In this work, three new kinds of bionic shaped cooling structures (T-type, Y-type, and H-type channels), are designed for the active cooling of the leading edge, which are compared with traditional parallel cooling structure (P-type), regarding the pressure penalty, maximum temperature, average Nusselt number, overall performance factor, and the cooling efficiency. Meanwhile, different coolant distribution strategies (constant supply, variable supply, and segmented supply strategy) are proposed to deal with the varied aerodynamic heating flux conditions when the hypersonic vehicle undergoes actual flight missions. The results show that the bionic shaped cooling channels have better cooling performances, with the maximum temperature of leading edge reduced by 673 K for the Y-type, 651 K for the T-type, and 525 K for the H-type channels at Re = 892. In addition, the variable supply strategy presents a relatively lower temperature and a more stable temperature variation for both the solid structure and coolant fluid, and so is the most suitable coolant distribution strategy.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109703"},"PeriodicalIF":4.9,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138061","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 : 2025-01-14DOI: 10.1016/j.ijthermalsci.2025.109690
Guillermo Federico Umbricht , Domingo Alberto Tarzia , Diana Rubio
In this work, a thermal energy transfer problem in a one-dimensional multilayer body is theoretically analyzed, considering diffusion, advection, internal heat generation or loss linearly dependent on temperature in each layer, as well as heat generation due to external sources. Additionally, the thermal contact resistance at the interfaces between each pair of materials is taken into account. The problem is mathematically modeled, and explicit analytical solutions are derived using Fourier techniques. A convergent finite difference scheme is also formulated to simulate specific cases. The solution is consistent with previous results. A numerical example is provided, demonstrating the coherence between the obtained results and the physical behavior of the problem. This work was recently published for a two-layer body; the generalization to -layer bodies allows for conclusions that enhance the theoretical understanding of heat transfer in multilayer materials and may contribute to improving the thermal design of multilayer engineering systems.
{"title":"Analytical and numerical study of a convection–diffusion–reaction–source problem in multilayered materials","authors":"Guillermo Federico Umbricht , Domingo Alberto Tarzia , Diana Rubio","doi":"10.1016/j.ijthermalsci.2025.109690","DOIUrl":"10.1016/j.ijthermalsci.2025.109690","url":null,"abstract":"<div><div>In this work, a thermal energy transfer problem in a one-dimensional multilayer body is theoretically analyzed, considering diffusion, advection, internal heat generation or loss linearly dependent on temperature in each layer, as well as heat generation due to external sources. Additionally, the thermal contact resistance at the interfaces between each pair of materials is taken into account. The problem is mathematically modeled, and explicit analytical solutions are derived using Fourier techniques. A convergent finite difference scheme is also formulated to simulate specific cases. The solution is consistent with previous results. A numerical example is provided, demonstrating the coherence between the obtained results and the physical behavior of the problem. This work was recently published for a two-layer body; the generalization to <span><math><mi>m</mi></math></span>-layer bodies allows for conclusions that enhance the theoretical understanding of heat transfer in multilayer materials and may contribute to improving the thermal design of multilayer engineering systems.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109690"},"PeriodicalIF":4.9,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138065","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109684
Changxin Lu , Chengzhi Lang , Jiawei Li , Chengyun Xin , Tuo Zhou , Tairan Fu
An integrally-molded double-sided spiral finned (IDSF) tube has been proposed in this paper to improve the thermal-hydraulic performance of the tubular air preheater due to the lower heat transfer efficiency, which limits its application in large units above 350 MW during the deep peaking. The physical model of IDSF tubes was established, and numerical simulations of the internal and external flow and heat transfer performance under different structural parameters were conducted. The simulation results show that adding spiral fins inside the tube will decrease the thermal-hydraulic performance inside the tube while adding spiral fins outside the tube with reasonable fin structure and arrangement parameters can increase the thermal-hydraulic performance outside the tube, and thus double-sided thermal-hydraulic performance evaluation factors have been proposed to evaluate the operation economy and compactness of air preheaters based on the Nu, j and f factors inside and outside the tube. Results show that the fin inside the tube has a significant effect on the pressure drop when the fin pitch is smaller than 12 mm, and the tubes with the fin heights of 1.5 mm and 2.0 mm exhibit excellent thermal-hydraulic performance at the fin pitch of 12 mm. The f of the tube with the fin height of 1.5 mm is lower than that of the tube with the fin height of 2.0 mm, and the f of the tube with the fin height of 2.0 mm is about 1.28 times that of the fin height of 1.5 mm. The volume of the tubular air preheater can be reduced by a maximum of 43.1 %∼46.0 %, while the power consumption increases by 14.7 %∼17.6 % compared to the smooth tube. The power consumption of the tubular air preheater can be reduced by a maximum of 19 %∼21 % and its volume reduced by 15.7 %∼16.7 %. This work provides essential theoretical guidance and technical support for the design and application of air preheaters.
{"title":"Numerical investigation on heat transfer enhancement by integrally-molded double-sided spiral finned tubes for waste heat recovery","authors":"Changxin Lu , Chengzhi Lang , Jiawei Li , Chengyun Xin , Tuo Zhou , Tairan Fu","doi":"10.1016/j.ijthermalsci.2025.109684","DOIUrl":"10.1016/j.ijthermalsci.2025.109684","url":null,"abstract":"<div><div>An integrally-molded double-sided spiral finned (IDSF) tube has been proposed in this paper to improve the thermal-hydraulic performance of the tubular air preheater due to the lower heat transfer efficiency, which limits its application in large units above 350 MW during the deep peaking. The physical model of IDSF tubes was established, and numerical simulations of the internal and external flow and heat transfer performance under different structural parameters were conducted. The simulation results show that adding spiral fins inside the tube will decrease the thermal-hydraulic performance inside the tube while adding spiral fins outside the tube with reasonable fin structure and arrangement parameters can increase the thermal-hydraulic performance outside the tube, and thus double-sided thermal-hydraulic performance evaluation factors have been proposed to evaluate the operation economy and compactness of air preheaters based on the <em>Nu</em>, <em>j</em> and <em>f</em> factors inside and outside the tube. Results show that the fin inside the tube has a significant effect on the pressure drop when the fin pitch is smaller than 12 mm, and the tubes with the fin heights of 1.5 mm and 2.0 mm exhibit excellent thermal-hydraulic performance at the fin pitch of 12 mm. The <em>f</em> of the tube with the fin height of 1.5 mm is lower than that of the tube with the fin height of 2.0 mm, and the <em>f</em> of the tube with the fin height of 2.0 mm is about 1.28 times that of the fin height of 1.5 mm. The volume of the tubular air preheater can be reduced by a maximum of 43.1 %∼46.0 %, while the power consumption increases by 14.7 %∼17.6 % compared to the smooth tube. The power consumption of the tubular air preheater can be reduced by a maximum of 19 %∼21 % and its volume reduced by 15.7 %∼16.7 %. This work provides essential theoretical guidance and technical support for the design and application of air preheaters.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109684"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138522","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109691
Yi Ru , Ali B.M. Ali , Karwan Hussein Qader , Hanaa Kadhim Abdulaali , Ramdevsinh Jhala , Saidjon Ismailov , Soheil Salahshour , Ali Mokhtarian
The accurate prediction of the rheological properties of nanofluids is critical for optimizing their application in various industrial systems. This study focuses on the dynamic viscosity prediction of MWCNT-Al2O3/water (80 %) and ethylene glycol (20 %) hybrid nanofluid using machine learning approaches. A multilayer perceptron neural network (MLPNN) was employed for viscosity prediction, and its structural and training parameters, including the number of hidden layers and neurons, learning rate, training technique, and transfer functions, were optimized using three metaheuristic algorithms: Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Marine Predators Algorithm (MPA). A dataset containing viscosity measurements influenced by nanoparticle volume fraction (VF), temperature (T), and shear rate (SR) was utilized. The optimization algorithms were evaluated over 10 and 20 runs for single-hidden-layer (1HL) and double-hidden-layer (2HL) MLPNNs, respectively. For the 1HL-MLPNN models, all three algorithms achieved nearly identical performance with high predictive accuracy (R = 0.99992, MSE = 0.00176). In contrast, for 2HL-MLPNN models, PSO outperformed MPA and GA with R = 0.99995 and MSE = 0.00105, followed by MPA (R = 0.99995, MSE = 0.00123) and GA (R = 0.99992, MSE = 0.00160). Also, sensitivity analysis revealed the VF as the most significant input parameter affecting viscosity predictions, followed by shear rate and temperature. These findings demonstrate the potential of metaheuristic-optimized MLPNNs for high-accuracy prediction of hybrid nanofluid rheological properties, facilitating improved design and application in thermal management systems.
{"title":"Accurate prediction of the rheological behavior of MWCNT-Al2O3/water-ethylene glycol nanofluid with metaheuristic-optimized machine learning models","authors":"Yi Ru , Ali B.M. Ali , Karwan Hussein Qader , Hanaa Kadhim Abdulaali , Ramdevsinh Jhala , Saidjon Ismailov , Soheil Salahshour , Ali Mokhtarian","doi":"10.1016/j.ijthermalsci.2025.109691","DOIUrl":"10.1016/j.ijthermalsci.2025.109691","url":null,"abstract":"<div><div>The accurate prediction of the rheological properties of nanofluids is critical for optimizing their application in various industrial systems. This study focuses on the dynamic viscosity prediction of MWCNT-Al<sub>2</sub>O<sub>3</sub>/water (80 %) and ethylene glycol (20 %) hybrid nanofluid using machine learning approaches. A multilayer perceptron neural network (MLPNN) was employed for viscosity prediction, and its structural and training parameters, including the number of hidden layers and neurons, learning rate, training technique, and transfer functions, were optimized using three metaheuristic algorithms: Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Marine Predators Algorithm (MPA). A dataset containing viscosity measurements influenced by nanoparticle volume fraction (VF), temperature (T), and shear rate (SR) was utilized. The optimization algorithms were evaluated over 10 and 20 runs for single-hidden-layer (1HL) and double-hidden-layer (2HL) MLPNNs, respectively. For the 1HL-MLPNN models, all three algorithms achieved nearly identical performance with high predictive accuracy (R = 0.99992, MSE = 0.00176). In contrast, for 2HL-MLPNN models, PSO outperformed MPA and GA with R = 0.99995 and MSE = 0.00105, followed by MPA (R = 0.99995, MSE = 0.00123) and GA (R = 0.99992, MSE = 0.00160). Also, sensitivity analysis revealed the VF as the most significant input parameter affecting viscosity predictions, followed by shear rate and temperature. These findings demonstrate the potential of metaheuristic-optimized MLPNNs for high-accuracy prediction of hybrid nanofluid rheological properties, facilitating improved design and application in thermal management systems.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109691"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138523","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109701
Zhaoxuan Liu, Li Shan, Wenming Li
Significantly enhanced thermal performance of mini-tubes is of vital importance to achieve high efficiency of heat exchangers. While existed studies have comprehensively investigated various inserts with an aim to enhance heat exchange performance by disrupting the core flow of mini-tube, the limitation of strong fluid mixing within the boundary layer remains unresolved. Herein, a novel chained-jet-chamber insert was proposed to generate strong jetting flow in the vertical direction of fluid flow. Therefore, fluid flow boundary layer was substantially disturbed, leading to the significant enhancement of heat exchange. Numerical investigation was conducted to characterize heat transfer characteristics of this as-designed mini-tube inserted with a chained-jet-chamber for Reynolds number (Re) changing from 200 to 1200. Numerical results show that the overall Nusselt number (Nu) is substantially improved to about 180 at a Re of 1200 with a significant enhancement of 5.5-fold compared to the tube without insert owing to the intense spatial fluid mixing induced by the strong jetting flows. To evaluate the overall effectiveness of this proposed insert, the performance evaluation criteria (PEC) was calculated. A value of 2.6 is presented at a Re of 200. In contrast, the PECs of the twisted tape and helical screw tape are 1.6 and 1.9, respectively. To conclude, this novel chained-jet-chamber insert completely outperforms the twisted tape and helical screw tape inserts by generating spatial fluid mixing. This new solution can significantly increase the efficiency of compact heat exchangers in practical applications.
{"title":"Enhanced thermal performance of mini-tube with chained-jet-chamber insert","authors":"Zhaoxuan Liu, Li Shan, Wenming Li","doi":"10.1016/j.ijthermalsci.2025.109701","DOIUrl":"10.1016/j.ijthermalsci.2025.109701","url":null,"abstract":"<div><div>Significantly enhanced thermal performance of mini-tubes is of vital importance to achieve high efficiency of heat exchangers. While existed studies have comprehensively investigated various inserts with an aim to enhance heat exchange performance by disrupting the core flow of mini-tube, the limitation of strong fluid mixing within the boundary layer remains unresolved. Herein, a novel chained-jet-chamber insert was proposed to generate strong jetting flow in the vertical direction of fluid flow. Therefore, fluid flow boundary layer was substantially disturbed, leading to the significant enhancement of heat exchange. Numerical investigation was conducted to characterize heat transfer characteristics of this as-designed mini-tube inserted with a chained-jet-chamber for Reynolds number (<em>Re</em>) changing from 200 to 1200. Numerical results show that the overall Nusselt number (<em>Nu</em>) is substantially improved to about 180 at a Re of 1200 with a significant enhancement of 5.5-fold compared to the tube without insert owing to the intense spatial fluid mixing induced by the strong jetting flows. To evaluate the overall effectiveness of this proposed insert, the performance evaluation criteria (PEC) was calculated. A value of 2.6 is presented at a Re of 200. In contrast, the PECs of the twisted tape and helical screw tape are 1.6 and 1.9, respectively. To conclude, this novel chained-jet-chamber insert completely outperforms the twisted tape and helical screw tape inserts by generating spatial fluid mixing. This new solution can significantly increase the efficiency of compact heat exchangers in practical applications.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109701"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138518","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109692
Yanhui Zhang , Rui Xu , Tiantian Zhang , Jie Yang , Yi Liu , Yingjun Liu , Jianli Wang
Thin-film materials are widely used in the field of thermal management, but the characterization of their thermophysical properties on the microscale is still challenging. In this work, the planar distribution of the cross-plane thermal diffusivity for microscale films is measured utilizing the location-variation and frequency-variation methods based on a laser spot periodic heating technique. A laser beam is focused on the film surface for periodic heating, while a thermocouple collects the temperature rise signal from the back surface. The in-plane thermal diffusivity is determined employing the phase lag spatial distribution of the temperature rise. The cross-plane thermal diffusivity is derived after correcting the frequency dependence of phase lag using the bias phase, thereby eliminating the effect of thermal contact resistance at the thermocouple junction. The accuracy of this method is verified by measuring the thermal diffusivity of standard anisotropic polyester and isotropic stainless-steel films. Finally, the planar distribution of cross-plane thermal diffusivity of microscale stainless-steel and reduced graphene oxide films are successfully measured, bridging the gap left by the infrared lock-in thermography technique.
{"title":"Planar distribution measurement of cross-plane thermal diffusivity for microscale films using laser spot periodic heating technique","authors":"Yanhui Zhang , Rui Xu , Tiantian Zhang , Jie Yang , Yi Liu , Yingjun Liu , Jianli Wang","doi":"10.1016/j.ijthermalsci.2025.109692","DOIUrl":"10.1016/j.ijthermalsci.2025.109692","url":null,"abstract":"<div><div>Thin-film materials are widely used in the field of thermal management, but the characterization of their thermophysical properties on the microscale is still challenging. In this work, the planar distribution of the cross-plane thermal diffusivity for microscale films is measured utilizing the location-variation and frequency-variation methods based on a laser spot periodic heating technique. A laser beam is focused on the film surface for periodic heating, while a thermocouple collects the temperature rise signal from the back surface. The in-plane thermal diffusivity is determined employing the phase lag spatial distribution of the temperature rise. The cross-plane thermal diffusivity is derived after correcting the frequency dependence of phase lag using the bias phase, thereby eliminating the effect of thermal contact resistance at the thermocouple junction. The accuracy of this method is verified by measuring the thermal diffusivity of standard anisotropic polyester and isotropic stainless-steel films. Finally, the planar distribution of cross-plane thermal diffusivity of microscale stainless-steel and reduced graphene oxide films are successfully measured, bridging the gap left by the infrared lock-in thermography technique.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109692"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138519","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109681
Yong Han , Yong-Gang Wu , Fan-Lin Meng , Can-Can Zhang , Yu-Ting Wu , Xue-Hong Wu , Ting-Xiang Jin
The optimization between heat transfer enhancement and flow resistance reduction of solar salt in a noncircular twisted tube heat exchanger (NCTTHX) was studied. Firstly, the effects of axis ratio (β), inlet velocity (uin,solarsalt) and pitch (Pt) on heat transfer and flow resistance of the solar salt were numerically investigated. Secondly, the mathematical model of the entropy balance for heat transfer process of the solar salt was established, where the modified heat transfer entropy generation number (HTEGN, χ) is proposed. Moreover, the modified ZS-RSM methodology was utilized for the regression of Nusselt number (Nuoval), heat transfer effectiveness (ε) and the HTEGN (χ). Finally, the integration of the NSGA-II algorithm and modified ZS-RSM methodology was utilized for the optimization of heat transfer enhancement and flow resistance reduction for solar salt in the NCTTHX. The results show that: the torsion force is the main reason that can improve the heat transfer performance, where ether the increase of β and uin,solarsalt or the decrease of Pt can strengthen the effect of the torsion force. There is a coincidence opposite variation trend between χ and ε at constant Re. χ can effectively describe the effect of changes in inlet temperature ratio tao on heat transfer performance, whereas ε cannot. The prediction by the modified ZS-RSM methodology is well aligned with the numerical results. When the minimum χ is added as the objective function, the flow resistance and heat transfer entropy generation number decreases by 6 % and 0.6 %, respectively; however, the energy efficiency ratio increases by 6.2 %.
{"title":"Multi-objective optimization study on heat transfer performance of solar salt in non-circular twisted tube heat exchanger based on entropy generation number and NSGA II","authors":"Yong Han , Yong-Gang Wu , Fan-Lin Meng , Can-Can Zhang , Yu-Ting Wu , Xue-Hong Wu , Ting-Xiang Jin","doi":"10.1016/j.ijthermalsci.2025.109681","DOIUrl":"10.1016/j.ijthermalsci.2025.109681","url":null,"abstract":"<div><div>The optimization between heat transfer enhancement and flow resistance reduction of solar salt in a noncircular twisted tube heat exchanger (NCTTHX) was studied. Firstly, the effects of axis ratio (<em>β</em>), inlet velocity (<em>u</em><sub><em>in,solar</em></sub> <sub><em>salt</em></sub>) and pitch (<em>P</em><sub><em>t</em></sub>) on heat transfer and flow resistance of the solar salt were numerically investigated. Secondly, the mathematical model of the entropy balance for heat transfer process of the solar salt was established, where the modified heat transfer entropy generation number (HTEGN, <em>χ</em>) is proposed. Moreover, the modified ZS-RSM methodology was utilized for the regression of Nusselt number (<em>Nu</em><sub><em>oval</em></sub>), heat transfer effectiveness (<em>ε</em>) and the HTEGN (<em>χ</em>). Finally, the integration of the NSGA-II algorithm and modified ZS-RSM methodology was utilized for the optimization of heat transfer enhancement and flow resistance reduction for solar salt in the NCTTHX. The results show that: the torsion force is the main reason that can improve the heat transfer performance, where ether the increase of <em>β</em> and <em>u</em><sub><em>in,solar</em></sub> <sub><em>salt</em></sub> or the decrease of <em>P</em><sub><em>t</em></sub> can strengthen the effect of the torsion force. There is a coincidence opposite variation trend between <em>χ</em> and <em>ε</em> at constant <em>Re</em>. <em>χ</em> can effectively describe the effect of changes in inlet temperature ratio <em>t</em><sub><em>ao</em></sub> on heat transfer performance, whereas <em>ε</em> cannot. The prediction by the modified ZS-RSM methodology is well aligned with the numerical results. When the minimum χ is added as the objective function, the flow resistance and heat transfer entropy generation number decreases by 6 % and 0.6 %, respectively; however, the energy efficiency ratio increases by 6.2 %.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109681"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138521","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109686
Rizos N. Krikkis
In the present study the stability, and the multiplicity features of ceramic fibers heated by microwave irradiation in a highly resonant cavity are numerically analyzed. The coupling of the electromagnetic and the temperature fields results in a reaction-diffusion nonlinear and nonlocal initial boundary value problem. The bifurcation analysis reveals a complex and interesting solution structure since the problem admits a large number of multiple solutions that have not been identified before. Up to thirteen temperature profiles have been obtained for certain values of the microwave power and the Conduction-Convection Parameter. An important finding is that the stable nonuniform and asymmetric temperature profiles that appear as the Conduction-Convection Parameter increases, featuring a low temperature on the one side of the fiber and a significantly higher one on the other side, are consistent with the localized thermal runaway that is experimentally observed when a cylindrical sample is heated in a microwave cavity and a hot temperature front is formed at the boundary and moves along the axis of the sample dramatically increasing the temperature at the far end while leaving the front end at a relatively low temperature. The mechanism triggering this localized thermal runaway is also explained on the basis of the multiple solutions obtained.
{"title":"Microwave heating of ceramic fibers. From multistability to thermal runaway","authors":"Rizos N. Krikkis","doi":"10.1016/j.ijthermalsci.2025.109686","DOIUrl":"10.1016/j.ijthermalsci.2025.109686","url":null,"abstract":"<div><div>In the present study the stability, and the multiplicity features of ceramic fibers heated by microwave irradiation in a highly resonant cavity are numerically analyzed. The coupling of the electromagnetic and the temperature fields results in a reaction-diffusion nonlinear and nonlocal initial boundary value problem. The bifurcation analysis reveals a complex and interesting solution structure since the problem admits a large number of multiple solutions that have not been identified before. Up to thirteen temperature profiles have been obtained for certain values of the microwave power and the Conduction-Convection Parameter. An important finding is that the stable nonuniform and asymmetric temperature profiles that appear as the Conduction-Convection Parameter increases, featuring a low temperature on the one side of the fiber and a significantly higher one on the other side, are consistent with the localized thermal runaway that is experimentally observed when a cylindrical sample is heated in a microwave cavity and a hot temperature front is formed at the boundary and moves along the axis of the sample dramatically increasing the temperature at the far end while leaving the front end at a relatively low temperature. The mechanism triggering this localized thermal runaway is also explained on the basis of the multiple solutions obtained.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109686"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143138524","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 : 2025-01-13DOI: 10.1016/j.ijthermalsci.2025.109705
Wei Sun , Peng Li , Tao Zhou , Yutong Li , Chongchong Li , Xiaodong Shao , Han Shen
Mini/micro-channel heat sinks with integrated impact jet offer significant potential for enhanced heat transfer performance. In this work, jet structures are integrated with four-inlet-two-outlet horizontal-flow heat sinks and the thermo-fluids performance is discussed. At first, four horizontal-flow heat sinks with diverse distributions of inlets and outlets locations are designed, using variable density topology optimization method with the minimization of average temperature and pressure drop as optimization objective. Among them, three are symmetric structures and one is asymmetric. Numerical simulations are conducted on the thermo-fluids performance of these four designs across six channel heights . The designs of MHS-A and MHS-B exhibit the highest cooling efficiency factor and best flow performance, respectively. In addition, the comprehensive performance evaluation of the asymmetric structure MHS-D is not the worst. Subsequently, a jet structure was integrated above the original horizontal flow path so that the vertically oriented fluid impinges on the horizontal flow path, forming the new cross-flow radiators IJMHS-A and IJMHS-B. Numerical results indicate that at a volume flow rate of 1152 ml/min and a jet ratio of 20 %, the average temperatures, maximum temperatures and temperature differences of IJMHS-A and IJMHS-B are reduced by 4.8 K, 6.8 K, 3.7K and 7.6 K, 10.8 K, 7.3K, respectively. A slight pressure drop loss is observed only for . The jet's gain of thermal performance decreases with increasing volume flow rate, displaying boundary effects. As the jet flow ratio rises, thermal performance initially improves, then declines, while the pressure drop increases at an accelerated rate. Optimal interval of the jet flow ratio is structure-dependent. For IJMHS-A and IJMHS-B, the best performance occurs with a jet flow ratio between 10 % and 30 %, combining benefits of both horizontal-flow topology and jet-flow structures. As the jet ratio continues to rise, the flow shifts from horizontal to jet characteristics, rapidly degrading heat transfer and flow performance. Numerical simulations are verified, aligning well with experimental results.
{"title":"Thermo-fluids performance analysis and experimental verification of topologically optimized mini-channel heat sinks integrated with impact jet","authors":"Wei Sun , Peng Li , Tao Zhou , Yutong Li , Chongchong Li , Xiaodong Shao , Han Shen","doi":"10.1016/j.ijthermalsci.2025.109705","DOIUrl":"10.1016/j.ijthermalsci.2025.109705","url":null,"abstract":"<div><div>Mini/micro-channel heat sinks with integrated impact jet offer significant potential for enhanced heat transfer performance. In this work, jet structures are integrated with four-inlet-two-outlet horizontal-flow heat sinks and the thermo-fluids performance is discussed. At first, four horizontal-flow heat sinks with diverse distributions of inlets and outlets locations are designed, using variable density topology optimization method with the minimization of average temperature and pressure drop as optimization objective. Among them, three are symmetric structures and one is asymmetric. Numerical simulations are conducted on the thermo-fluids performance of these four designs across six channel heights <span><math><mrow><msub><mi>H</mi><mi>m</mi></msub></mrow></math></span>. The designs of MHS-A and MHS-B exhibit the highest cooling efficiency factor <span><math><mrow><msub><mi>j</mi><mi>c</mi></msub></mrow></math></span> and best flow performance, respectively. In addition, the comprehensive performance evaluation of the asymmetric structure MHS-D is not the worst. Subsequently, a jet structure was integrated above the original horizontal flow path so that the vertically oriented fluid impinges on the horizontal flow path, forming the new cross-flow radiators IJMHS-A and IJMHS-B. Numerical results indicate that at a volume flow rate of 1152 ml/min and a jet ratio of 20 %, the average temperatures, maximum temperatures and temperature differences of IJMHS-A and IJMHS-B are reduced by 4.8 K, 6.8 K, 3.7K and 7.6 K, 10.8 K, 7.3K, respectively. A slight pressure drop loss is observed only for <span><math><mrow><msub><mi>H</mi><mi>m</mi></msub><mo>≥</mo><mn>3</mn><mi>m</mi><mi>m</mi></mrow></math></span>. The jet's gain of thermal performance decreases with increasing volume flow rate, displaying boundary effects. As the jet flow ratio rises, thermal performance initially improves, then declines, while the pressure drop increases at an accelerated rate. Optimal interval of the jet flow ratio is structure-dependent. For IJMHS-A and IJMHS-B, the best performance occurs with a jet flow ratio between 10 % and 30 %, combining benefits of both horizontal-flow topology and jet-flow structures. As the jet ratio continues to rise, the flow shifts from horizontal to jet characteristics, rapidly degrading heat transfer and flow performance. Numerical simulations are verified, aligning well with experimental results.</div></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":"211 ","pages":"Article 109705"},"PeriodicalIF":4.9,"publicationDate":"2025-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143137953","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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