Pub Date : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.130000
Ivan Talão Martins , Alberto Ramil Rego , Pablo Fariñas Alvariño , Luben Cabezas-Gómez
Assessment of pool boiling crisis (Critical Heat Flux - CHF - and its corresponding superheating) is of utmost importance for industrial purposes. This research pays special attention to both the temperature excursion before CHF and its corresponding uncertainty under a wide range of pressures and surface treatments. This experimental approach studies the pool boiling phenomena of saturated Novec HFE-7100 under four different pressures, namely 25, 50, 100, and 200 kPa. Six copper boiling surfaces are reported: four grinded with four different levels of sandpaper and two structured surfaces, crafted by a femtosecond laser. The roughness of the laser surfaces is within that yielded through the grinding procedure, which is interesting for comparison purposes. The yielded results show outstanding evidence: (i) The surface roughness does not modify the CHF for low pressures, which suggests the pertinence to address and determine what a plain surface is for nucleate boiling and (ii) even though both laser treatments enhance the CHF, one of the treatments yielded superheatings for CHF similar to those of the polished test section. It seems that the re-wetting mechanism promoted by the laser treatment is somehow delayed, and thus, enhances the pool boiling feasibility for a wider unexpected range of temperatures.
{"title":"Experimental study of structured and unstructured roughness impact on the CHF of HFE-7100 for different saturation pressures","authors":"Ivan Talão Martins , Alberto Ramil Rego , Pablo Fariñas Alvariño , Luben Cabezas-Gómez","doi":"10.1016/j.applthermaleng.2026.130000","DOIUrl":"10.1016/j.applthermaleng.2026.130000","url":null,"abstract":"<div><div>Assessment of pool boiling crisis (Critical Heat Flux - CHF - and its corresponding superheating) is of utmost importance for industrial purposes. This research pays special attention to both the temperature excursion before CHF and its corresponding uncertainty under a wide range of pressures and surface treatments. This experimental approach studies the pool boiling phenomena of saturated Novec HFE-7100 under four different pressures, namely 25, 50, 100, and 200 kPa. Six copper boiling surfaces are reported: four grinded with four different levels of sandpaper and two structured surfaces, crafted by a femtosecond laser. The roughness of the laser surfaces is within that yielded through the grinding procedure, which is interesting for comparison purposes. The yielded results show outstanding evidence: (i) The surface roughness does not modify the CHF for low pressures, which suggests the pertinence to address and determine what a plain surface is for nucleate boiling and (ii) even though both laser treatments enhance the CHF, one of the treatments yielded superheatings for CHF similar to those of the polished test section. It seems that the re-wetting mechanism promoted by the laser treatment is somehow delayed, and thus, enhances the pool boiling feasibility for a wider unexpected range of temperatures.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 130000"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074370","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 : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.129990
Wenwen Cui , Xiaoqiang Dong , Shiqi Chang , Xiaoqiang Li , Wuhu Huang , Jiashi Li
Low-grade near-surface heat is abundant but difficult to utilize efficiently. This study develops a field-validated, end-to-end workflow that links thermosyphon heat delivery to net electric power and provides design guidance across sites. The multiscale framework combines a three-dimensional two-phase flow-and-heat-transfer model, a steady thermal-resistance network, and a three-node transient thermal network, and couples the predicted heat delivery to a micro organic Rankine cycle using off-design efficiency maps, exergy analysis, and proportional–integral control. A physics-informed surrogate is trained with repeated cross-validation and bootstrap-based uncertainty estimation. Field measurements indicate stable thin-film operation with one-way ammonia vapor transport; the evaporator wall remains near 5 °C and the condenser near 0–1 °C, with wall heat flux exceeding 360 W m−2 in the heated section. The transient network reproduces measured heat input with a normalized root-mean-square error of 0.0086 and a mean absolute percentage error of 2.30%, while steady predictions agree with the three-dimensional results within 1–3%. The surrogate identifies condenser-side heat transfer and thermal contact resistance as dominant drivers, suggesting practical targets of at least 35 W m−2 K−1 and no more than 0.03 m2 K W−1, respectively. Multi-objective screening yields Pareto-efficient designs that reduce cost and warming impact while maintaining net power output.
低品位近地表热量丰富，但难以有效利用。本研究开发了一种现场验证的端到端工作流程，将热虹吸热量输送与净电力联系起来，并提供跨站点的设计指导。该多尺度框架结合了三维两相流动和传热模型、稳定热阻网络和三节点瞬态热网络，并使用非设计效率图、火用分析和比例积分控制将预测的热量传递耦合到微有机朗肯循环中。通过反复交叉验证和基于引导的不确定性估计来训练物理信息代理。现场测量表明，在单向氨蒸汽输送下，薄膜运行稳定；蒸发器壁面保持在5℃附近，冷凝器保持在0 ~ 1℃附近，受热段壁面热流密度大于360 W m−2。瞬态网络模拟的实测热输入的归一化均方根误差为0.0086，平均绝对百分比误差为2.30%，而稳态网络预测与三维结果的一致性在1-3%以内。该替代方法将冷凝器侧传热和热接触阻力确定为主要驱动因素，建议实际目标分别为至少35 W m−2 K−1和不超过0.03 m2 K W−1。多目标筛选产生了帕累托效率设计，在保持净功率输出的同时降低了成本和变暖影响。
{"title":"Multiscale modeling and optimization of a thermosyphon system using a field-validated CFD–thermal-network framework","authors":"Wenwen Cui , Xiaoqiang Dong , Shiqi Chang , Xiaoqiang Li , Wuhu Huang , Jiashi Li","doi":"10.1016/j.applthermaleng.2026.129990","DOIUrl":"10.1016/j.applthermaleng.2026.129990","url":null,"abstract":"<div><div>Low-grade near-surface heat is abundant but difficult to utilize efficiently. This study develops a field-validated, end-to-end workflow that links thermosyphon heat delivery to net electric power and provides design guidance across sites. The multiscale framework combines a three-dimensional two-phase flow-and-heat-transfer model, a steady thermal-resistance network, and a three-node transient thermal network, and couples the predicted heat delivery to a micro organic Rankine cycle using off-design efficiency maps, exergy analysis, and proportional–integral control. A physics-informed surrogate is trained with repeated cross-validation and bootstrap-based uncertainty estimation. Field measurements indicate stable thin-film operation with one-way ammonia vapor transport; the evaporator wall remains near 5 °C and the condenser near 0–1 °C, with wall heat flux exceeding 360 W m<sup>−2</sup> in the heated section. The transient network reproduces measured heat input with a normalized root-mean-square error of 0.0086 and a mean absolute percentage error of 2.30%, while steady predictions agree with the three-dimensional results within 1–3%. The surrogate identifies condenser-side heat transfer and thermal contact resistance as dominant drivers, suggesting practical targets of at least 35 W m<sup>−2</sup> K<sup>−1</sup> and no more than 0.03 m<sup>2</sup> K W<sup>−1</sup>, respectively. Multi-objective screening yields Pareto-efficient designs that reduce cost and warming impact while maintaining net power output.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129990"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074749","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 : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.130002
Jiawei Li , Tianyuan Yang , Yurui Mao , Xiaoguang Li , Zhengqi Li
To solve the problems of upward movement of flame center, slagging, and NOx emissions in traditional down fired boilers when burning high volatile bituminous coal, this study proposes an innovative coupling strategy based on primary air bias combustion technology (PABCT): primary air biased technology coupled with precise furnace gas port tuning (PAFPT). However, the core mechanism of how the position of the vent air position regulates the spatiotemporal evolution of the gas solid two phase of the biased primary air jet is not yet clear, and there is a lack of quantitative optimization basis. Therefore, a 1:20 cold state gas solid two phase modeling test bench was established to systematically study the flow characteristics under different vent air nozzle positions (55 mm, 95 mm, 145 mm, 195 mm), with precise measurements conducted using 3D-Phase Doppler Particle Anemometer (PDA). For the first time, this study combines main effect and interaction effect analysis to quantitatively reveal the core mechanism of vent air position. The results show that vent air position is the key to controlling the timing of gas-solid mixing and entrainment intensity: the high-position arrangement at 55 mm leads to premature mixing, which is unfavorable for stable combustion and NOx control; the low-position arrangement at 195 mm causes premature particle deflection and insufficient downward momentum. Multi-index joint optimization analysis identifies 145 mm as the global optimal operating condition. Under this condition, the peak particle volume flow rate in the cold ash hopper area reaches 1.64–2.25 times that of other conditions, and the gas-solid velocity and pulsation characteristics achieve the best synergy. This can effectively delay pulverized coal ignition, reconstruct the “W”-shaped flame, thereby improving the lower furnace utilization rate and pulverized coal burnout rate, and laying a flow field foundation for reducing NOx generation at the source. Through a data-driven optimization method, this study provides a solid theoretical basis and universal optimization strategy for the design and operation of down fire boilers, contributing to the clean and efficient utilization of coal.
{"title":"A novel high-efficiency and low-nitrogen combustion technology for down-fired boilers: Vent air position on gas-solid flow characteristics with biased primary air and control strategy","authors":"Jiawei Li , Tianyuan Yang , Yurui Mao , Xiaoguang Li , Zhengqi Li","doi":"10.1016/j.applthermaleng.2026.130002","DOIUrl":"10.1016/j.applthermaleng.2026.130002","url":null,"abstract":"<div><div>To solve the problems of upward movement of flame center, slagging, and NO<sub><em>x</em></sub> emissions in traditional down fired boilers when burning high volatile bituminous coal, this study proposes an innovative coupling strategy based on primary air bias combustion technology (PABCT): primary air biased technology coupled with precise furnace gas port tuning (PAFPT). However, the core mechanism of how the position of the vent air position regulates the spatiotemporal evolution of the gas solid two phase of the biased primary air jet is not yet clear, and there is a lack of quantitative optimization basis. Therefore, a 1:20 cold state gas solid two phase modeling test bench was established to systematically study the flow characteristics under different vent air nozzle positions (55 mm, 95 mm, 145 mm, 195 mm), with precise measurements conducted using 3D-Phase Doppler Particle Anemometer (PDA). For the first time, this study combines main effect and interaction effect analysis to quantitatively reveal the core mechanism of vent air position. The results show that vent air position is the key to controlling the timing of gas-solid mixing and entrainment intensity: the high-position arrangement at 55 mm leads to premature mixing, which is unfavorable for stable combustion and NO<sub><em>x</em></sub> control; the low-position arrangement at 195 mm causes premature particle deflection and insufficient downward momentum. Multi-index joint optimization analysis identifies 145 mm as the global optimal operating condition. Under this condition, the peak particle volume flow rate in the cold ash hopper area reaches 1.64–2.25 times that of other conditions, and the gas-solid velocity and pulsation characteristics achieve the best synergy. This can effectively delay pulverized coal ignition, reconstruct the “W”-shaped flame, thereby improving the lower furnace utilization rate and pulverized coal burnout rate, and laying a flow field foundation for reducing NO<sub><em>x</em></sub> generation at the source. Through a data-driven optimization method, this study provides a solid theoretical basis and universal optimization strategy for the design and operation of down fire boilers, contributing to the clean and efficient utilization of coal.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"290 ","pages":"Article 130002"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146096150","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 : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.129915
Yaran Wang , Shangzhou Ma , Lanxiang Yang , Jingyu Wu , Yan Jiang , Liwen Wang , Shen Wei
Multi-source district heating systems often exhibit low efficiency and high operating costs due to the strong coupling between primary heat supply and peak-shaving boilers, especially under time-varying thermal demand. This study proposes a forecast-driven, data-driven coordinated optimization framework to improve system-level operation. A stacked learning model is developed to predict hourly heating demand using historical load and meteorological data, and the forecasts are embedded into a coordinated control strategy for dynamic heat allocation between a combined heat and power supply and a peak-shaving boiler house. The framework is validated on a real multi-source district heating system in Tianjin, China. The peak-shaving boiler house consists of five gas boilers with a rated capacity of 70 MW each and three gas boilers with a rated capacity of 29 MW each, resulting in a total installed capacity of 437 MW, and the system is equipped with four plate heat exchangers. The forecasting model achieves a coefficient of determination of 0.989 and an average relative error of 2.0%. By applying a sliding-window dynamic convex optimization strategy, total gas consumption is reduced by 5.41%, boiler start–stop frequency decreases by 25%, and average boiler efficiency increases to 94.22%. By bridging load forecasting and operational optimization, the proposed framework enables stable long-horizon coordination of peak-shaving boilers and provides a reproducible and transferable solution for multi-source district heating systems.
{"title":"Data-driven optimization of multi-Source District heating systems based on load forecasting and coordinated control","authors":"Yaran Wang , Shangzhou Ma , Lanxiang Yang , Jingyu Wu , Yan Jiang , Liwen Wang , Shen Wei","doi":"10.1016/j.applthermaleng.2026.129915","DOIUrl":"10.1016/j.applthermaleng.2026.129915","url":null,"abstract":"<div><div>Multi-source district heating systems often exhibit low efficiency and high operating costs due to the strong coupling between primary heat supply and peak-shaving boilers, especially under time-varying thermal demand. This study proposes a forecast-driven, data-driven coordinated optimization framework to improve system-level operation. A stacked learning model is developed to predict hourly heating demand using historical load and meteorological data, and the forecasts are embedded into a coordinated control strategy for dynamic heat allocation between a combined heat and power supply and a peak-shaving boiler house. The framework is validated on a real multi-source district heating system in Tianjin, China. The peak-shaving boiler house consists of five gas boilers with a rated capacity of 70 MW each and three gas boilers with a rated capacity of 29 MW each, resulting in a total installed capacity of 437 MW, and the system is equipped with four plate heat exchangers. The forecasting model achieves a coefficient of determination of 0.989 and an average relative error of 2.0%. By applying a sliding-window dynamic convex optimization strategy, total gas consumption is reduced by 5.41%, boiler start–stop frequency decreases by 25%, and average boiler efficiency increases to 94.22%. By bridging load forecasting and operational optimization, the proposed framework enables stable long-horizon coordination of peak-shaving boilers and provides a reproducible and transferable solution for multi-source district heating systems.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"290 ","pages":"Article 129915"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146096132","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 : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.129934
Yuan Ma , Yingjie Tang , Junlong Zhao , Jiawei Yang , Pingjian Ming
Direct numerical simulations (DNS) of transcritical channel flow were performed to address the longstanding challenge of predicting heat transfer under high-pressure, strong property-variation conditions. Fukagata-Iwamoto-Kasagi (FIK) decomposition of the Nusselt number revealed that the contribution from the wall-parallel mean velocity is non-negligible at the channel center and can dominate the turbulent heat flux, a finding in sharp contrast to classical compressible flow behavior. Comparison with Reynolds-averaged Navier–Stokes (RANS) predictions reveals that, under the present low-Re, high-density-ratio conditions, the Nusselt number is over-estimated by 20–40% relative to DNS. Root-cause analysis shows that this discrepancy stems from the wall-normal velocity component that RANS under-resolves the density–velocity covariance term, which DNS reveals to supply up to 40% of the turbulent heat flux through coherent ejection–sweep events across the pseudo-critical density gradient, is absent in conventional closures. Capitalizing on the DNS data, a physics-based five-parameter correlation was developed that collapses the scattered Nusselt number data within ±25% error band. The work thus identifies the missing covariance term as the root cause of RANS inaccuracy in transcritical flows and provides an immediately applicable predictive tool for the thermal design of compact heat exchangers and micro-channels.
{"title":"Physics-based heat transfer correlation for transcritical channel flows and RANS evaluation in wall-normal momentum and heat flux prediction","authors":"Yuan Ma , Yingjie Tang , Junlong Zhao , Jiawei Yang , Pingjian Ming","doi":"10.1016/j.applthermaleng.2026.129934","DOIUrl":"10.1016/j.applthermaleng.2026.129934","url":null,"abstract":"<div><div>Direct numerical simulations (DNS) of transcritical channel flow were performed to address the longstanding challenge of predicting heat transfer under high-pressure, strong property-variation conditions. Fukagata-Iwamoto-Kasagi (FIK) decomposition of the Nusselt number revealed that the contribution from the wall-parallel mean velocity is non-negligible at the channel center and can dominate the turbulent heat flux, a finding in sharp contrast to classical compressible flow behavior. Comparison with Reynolds-averaged Navier–Stokes (RANS) predictions reveals that, under the present low-<em>Re</em>, high-density-ratio conditions, the Nusselt number is over-estimated by 20–40% relative to DNS. Root-cause analysis shows that this discrepancy stems from the wall-normal velocity component that RANS under-resolves the density–velocity covariance term, which DNS reveals to supply up to 40% of the turbulent heat flux through coherent ejection–sweep events across the pseudo-critical density gradient, is absent in conventional closures. Capitalizing on the DNS data, a physics-based five-parameter correlation was developed that collapses the scattered Nusselt number data within ±25% error band. The work thus identifies the missing covariance term as the root cause of RANS inaccuracy in transcritical flows and provides an immediately applicable predictive tool for the thermal design of compact heat exchangers and micro-channels.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"290 ","pages":"Article 129934"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146096191","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 : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.129878
Qingfan Liu , Guiping Zhou , Shuo Zhang , Zilong Zeng , Chenglin Fu , Baichuan He , Yu Zhou , Dengwei Jing
This study proposes an innovative photovoltaic and concentrated thermoelectric generator (PV-CTEG) hybrid system based on spectral beam splitting. The optical and thermoelectric coupling properties were investigated using TracePro and ANSYS. It was found that the hot side TEG surface achieves a uniform energy flux density distribution after solar concentration. With sun tracking error increasing from 0.0° to 0.5°, the normalized optical efficiency decreases from 94.71% to 89.01% for a north-south error and to 90.35% for an east-west error. Thermodynamic analysis indicates that at a radiation flux density of 900 W m−2, the hybrid system generates a total electrical output of 10.35 W, consisting of 10.10 W from the solar cells and 0.25 W from the TEG, yielding an overall energy conversion efficiency of 20.77%. This demonstrates that the TEG recovers part of the spectral thermal energy and enables stepwise utilization. The effects of radiation flux density, geometric concentration ratio, external load resistance, and solar cell operating temperature were also investigated. It turns out that higher radiant flux density and concentration ratio improve the system's conversion efficiency, while the maximum efficiency is obtained when the external load resistance approaches the TEG's total internal resistance. However, increasing the solar cells temperature reduces PV conversion efficiency, thereby lowering overall performance. Simulations using real-weather data from diverse climatic zones confirm the system's operational stability and superior performance in high-irradiation regions, validating its feasibility for efficient, cascaded solar energy harvesting.
本文提出了一种基于光谱分束的光伏-聚光热电发电（PV-CTEG）混合系统。利用TracePro和ANSYS对其光学和热电耦合特性进行了研究。发现热侧TEG表面在太阳集中后能量通量密度分布较为均匀。当太阳跟踪误差从0.0°增加到0.5°时，南北误差的归一化光学效率从94.71%下降到89.01%，东西误差的归一化光学效率下降到90.35%。热力学分析表明，在辐射通量密度为900 W m−2时，混合动力系统的总输出功率为10.35 W，其中太阳能电池输出功率为10.10 W， TEG输出功率为0.25 W，总能量转换效率为20.77%。这表明TEG回收了部分光谱热能，可以逐步利用。研究了辐射通量密度、几何浓度比、外负载电阻和太阳电池工作温度等因素的影响。结果表明，较高的辐射通量密度和浓度比提高了系统的转换效率，而当外部负载电阻接近TEG的总内阻时，系统的转换效率达到最大。然而，提高太阳能电池温度会降低PV转换效率，从而降低整体性能。利用来自不同气候带的真实天气数据进行模拟，证实了该系统在高辐射区域的运行稳定性和卓越性能，验证了其高效、级联太阳能收集的可行性。
{"title":"Optical and thermodynamic study of a novel photovoltaic and concentrated thermoelectric generator (PV-CTEG) hybrid system based on spectral beam splitting technology","authors":"Qingfan Liu , Guiping Zhou , Shuo Zhang , Zilong Zeng , Chenglin Fu , Baichuan He , Yu Zhou , Dengwei Jing","doi":"10.1016/j.applthermaleng.2026.129878","DOIUrl":"10.1016/j.applthermaleng.2026.129878","url":null,"abstract":"<div><div>This study proposes an innovative photovoltaic and concentrated thermoelectric generator (PV-CTEG) hybrid system based on spectral beam splitting. The optical and thermoelectric coupling properties were investigated using TracePro and ANSYS. It was found that the hot side TEG surface achieves a uniform energy flux density distribution after solar concentration. With sun tracking error increasing from 0.0° to 0.5°, the normalized optical efficiency decreases from 94.71% to 89.01% for a north-south error and to 90.35% for an east-west error. Thermodynamic analysis indicates that at a radiation flux density of 900 W m<sup>−2</sup>, the hybrid system generates a total electrical output of 10.35 W, consisting of 10.10 W from the solar cells and 0.25 W from the TEG, yielding an overall energy conversion efficiency of 20.77%. This demonstrates that the TEG recovers part of the spectral thermal energy and enables stepwise utilization. The effects of radiation flux density, geometric concentration ratio, external load resistance, and solar cell operating temperature were also investigated. It turns out that higher radiant flux density and concentration ratio improve the system's conversion efficiency, while the maximum efficiency is obtained when the external load resistance approaches the TEG's total internal resistance. However, increasing the solar cells temperature reduces PV conversion efficiency, thereby lowering overall performance. Simulations using real-weather data from diverse climatic zones confirm the system's operational stability and superior performance in high-irradiation regions, validating its feasibility for efficient, cascaded solar energy harvesting.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129878"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074823","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 : 2026-01-27DOI: 10.1016/j.applthermaleng.2026.129999
Liu Yang , Xin Gongming , Chen Yan , Song Mingda , Shen Xiaomin , Song Yunjia
In this study, a novel sintered composite wick for loop heat pipes (LHPs) was designed and fabricated, featuring a high effective thermal conductivity (ETC) nickel layer adjacent to the evaporator and a low effective thermal conductivity PTFE layer near the compensation chamber. The effective thermal conductivity difference between the two layers reaches approximately 10-fold, significantly greater than the 1.5–3.5 range reported for conventional composite wicks. The synergistic combination of nickel's rapid heat spreading and PTFE's thermal insulation, coupled with PTFE's intrinsic biporous structure, enables simultaneous enhancement of evaporation efficiency and heat leak suppression. Specifically, the LHP using the composite wick achieved a thermal resistance reduction of about 40%, and a steady-state operating temperature decrease of approximately 10–20% compared to the high-ETC nickel wick. Moreover, under low heating power (5 W), the start-up time was shortened by up to 65% compared to the low-ETC PTFE wick. These findings demonstrate that incorporating a large ETC gradient into the wick structure significantly enhances the thermal performance of LHPs, offering a promising approach for next-generation miniature and high-efficiency thermal management systems.
{"title":"Ultra-high thermal conductivity gradient composite Wick for loop heat pipes","authors":"Liu Yang , Xin Gongming , Chen Yan , Song Mingda , Shen Xiaomin , Song Yunjia","doi":"10.1016/j.applthermaleng.2026.129999","DOIUrl":"10.1016/j.applthermaleng.2026.129999","url":null,"abstract":"<div><div>In this study, a novel sintered composite wick for loop heat pipes (LHPs) was designed and fabricated, featuring a high effective thermal conductivity (ETC) nickel layer adjacent to the evaporator and a low effective thermal conductivity PTFE layer near the compensation chamber. The effective thermal conductivity difference between the two layers reaches approximately 10-fold, significantly greater than the 1.5–3.5 range reported for conventional composite wicks. The synergistic combination of nickel's rapid heat spreading and PTFE's thermal insulation, coupled with PTFE's intrinsic biporous structure, enables simultaneous enhancement of evaporation efficiency and heat leak suppression. Specifically, the LHP using the composite wick achieved a thermal resistance reduction of about 40%, and a steady-state operating temperature decrease of approximately 10–20% compared to the high-ETC nickel wick. Moreover, under low heating power (5 W), the start-up time was shortened by up to 65% compared to the low-ETC PTFE wick. These findings demonstrate that incorporating a large ETC gradient into the wick structure significantly enhances the thermal performance of LHPs, offering a promising approach for next-generation miniature and high-efficiency thermal management systems.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129999"},"PeriodicalIF":6.9,"publicationDate":"2026-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074443","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 : 2026-01-26DOI: 10.1016/j.applthermaleng.2026.129987
Armin Esmaeilzadeh , Kourosh Javaherdeh , Mohammad Naghashzadegan , Ahmed Rezk
Considering the significant share of natural gas in the world energy sources reducing the emission in distribution chain is very important and managing the boil-off gas has a substantial role in this context. A novel process for boil-off gas re-liquefaction based on an active magnetic regenerative cryocooler integrated with a cold energy storage unit is proposed and analysed. The active magnetic regenerative refrigeration section of the system consists of nine active magnetic regenerative cryocooler units, each comprising five stages and producing a 37 K temperature span using permanent magnets with a magnetic field strength of 1.5 Tesla. Propane is selected as the heat transfer fluid due to its wide availability and cost-effectiveness. The system includes a closed-loop heat sink cooled by a nitrogen-enriched vapour-compression unit operating at a maximum pressure of 12 bar. A computational one-dimensional model is applied to simulate thermodynamic and heat transfer processes in the regenerators. Key performance parameters including specific energy consumption, exergy efficiency, coefficient of performance, and liquefaction capacity are reported, and finally a comprehensive economic analysis is conducted to evaluate the costs through the proposed process. The proposed system achieves a specific energy consumption of 0.7816 kWh/kgLNG, an exergy efficiency of 0.4192, a coefficient of performance of 0.3396. An 11.7% reduction in specific energy consumption, a 44% improvement in coefficient of performance, 29% increase in exergy efficiency in comparison with currently in use systems and a liquefaction capacity of approximately 90% demonstrate the potential of the active magnetic regenerative refrigeration-based re-liquefaction system to provide an efficient and cost-effective alternative to traditional boil-off gas re-liquefaction systems. The proposed re-liquefaction system provides advantage of eliminating the need for cold boxes and multi-stream heat exchangers, thereby reducing process complexity, lowering reliance on in-port maintenance, and significantly improving scalability. Additionally, the economic analysis shows that, compared with the most widely used commercial LNG carrier re-liquefaction system, it enables noticeable downsizing, with purchased costs of the compressors, heat exchangers, and turbo expanders reduced by approximately 12.6%, 36.6%, and 12.6%, respectively.
{"title":"Conceptual design and analysis of a boil-off gas re-liquefaction process driven by a multi-stage active magnetic regenerative cryocooler","authors":"Armin Esmaeilzadeh , Kourosh Javaherdeh , Mohammad Naghashzadegan , Ahmed Rezk","doi":"10.1016/j.applthermaleng.2026.129987","DOIUrl":"10.1016/j.applthermaleng.2026.129987","url":null,"abstract":"<div><div>Considering the significant share of natural gas in the world energy sources reducing the emission in distribution chain is very important and managing the boil-off gas has a substantial role in this context. A novel process for boil-off gas re-liquefaction based on an active magnetic regenerative cryocooler integrated with a cold energy storage unit is proposed and analysed. The active magnetic regenerative refrigeration section of the system consists of nine active magnetic regenerative cryocooler units, each comprising five stages and producing a 37 K temperature span using permanent magnets with a magnetic field strength of 1.5 Tesla. Propane is selected as the heat transfer fluid due to its wide availability and cost-effectiveness. The system includes a closed-loop heat sink cooled by a nitrogen-enriched vapour-compression unit operating at a maximum pressure of 12 bar. A computational one-dimensional model is applied to simulate thermodynamic and heat transfer processes in the regenerators. Key performance parameters including specific energy consumption, exergy efficiency, coefficient of performance, and liquefaction capacity are reported, and finally a comprehensive economic analysis is conducted to evaluate the costs through the proposed process. The proposed system achieves a specific energy consumption of 0.7816 kWh/kg<sub>LNG</sub>, an exergy efficiency of 0.4192, a coefficient of performance of 0.3396. An 11.7% reduction in specific energy consumption, a 44% improvement in coefficient of performance, 29% increase in exergy efficiency in comparison with currently in use systems and a liquefaction capacity of approximately 90% demonstrate the potential of the active magnetic regenerative refrigeration-based re-liquefaction system to provide an efficient and cost-effective alternative to traditional boil-off gas re-liquefaction systems. The proposed re-liquefaction system provides advantage of eliminating the need for cold boxes and multi-stream heat exchangers, thereby reducing process complexity, lowering reliance on in-port maintenance, and significantly improving scalability. Additionally<strong>,</strong> the economic analysis shows that, compared with the most widely used commercial LNG carrier re-liquefaction system, it enables noticeable downsizing, with purchased costs of the compressors, heat exchangers, and turbo expanders reduced by approximately 12.6%, 36.6%, and 12.6%, respectively.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129987"},"PeriodicalIF":6.9,"publicationDate":"2026-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074585","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 : 2026-01-26DOI: 10.1016/j.applthermaleng.2026.129919
Yunseo Kim , Daeyoung Kong , Jeonghwan Park , Bongho Jang , Taeyeon Kim , Hyuk-Jun Kwon , Jungwan Cho , Jung Bin In , Hyoungsoon Lee
Effective thermal management in power devices is essential for energy-efficient operation. Pool boiling dissipates heat effectively through passive phase changes, eliminating the need for pumping power. However, these benefits remain unrealized in high-power-density devices owing to the risk of reaching Critical Heat Flux (CHF). The superior heat-spreading capabilities of diamond can help mitigate excessive heat flux in such devices. Consequently, pool boiling on diamond surfaces represents a promising cooling strategy for devices with high power densities. However, the inherent chemical inertness of diamond severely limits its surface modification, thereby posing significant challenges to the control of interfacial phenomena. This study investigated methods to modify Polycrystalline Diamond (PCD) surfaces to enhance their pool boiling performance. Thermal oxidation efficiently altered the PCD surface, exploiting its unique material properties. The enhanced surface enabled a 47.8% increase in the heat transfer coefficient and a 119.4% increase in the CHF. Additionally, an in-depth investigation clarified how structural and chemical modifications induced by high-temperature oxidation enhanced pool boiling performance.
{"title":"Thermally induced structural evolution of diamond surface for pool boiling enhancement","authors":"Yunseo Kim , Daeyoung Kong , Jeonghwan Park , Bongho Jang , Taeyeon Kim , Hyuk-Jun Kwon , Jungwan Cho , Jung Bin In , Hyoungsoon Lee","doi":"10.1016/j.applthermaleng.2026.129919","DOIUrl":"10.1016/j.applthermaleng.2026.129919","url":null,"abstract":"<div><div>Effective thermal management in power devices is essential for energy-efficient operation. Pool boiling dissipates heat effectively through passive phase changes, eliminating the need for pumping power. However, these benefits remain unrealized in high-power-density devices owing to the risk of reaching Critical Heat Flux (CHF). The superior heat-spreading capabilities of diamond can help mitigate excessive heat flux in such devices. Consequently, pool boiling on diamond surfaces represents a promising cooling strategy for devices with high power densities. However, the inherent chemical inertness of diamond severely limits its surface modification, thereby posing significant challenges to the control of interfacial phenomena. This study investigated methods to modify Polycrystalline Diamond (PCD) surfaces to enhance their pool boiling performance. Thermal oxidation efficiently altered the PCD surface, exploiting its unique material properties. The enhanced surface enabled a 47.8% increase in the heat transfer coefficient and a 119.4% increase in the CHF. Additionally, an in-depth investigation clarified how structural and chemical modifications induced by high-temperature oxidation enhanced pool boiling performance.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129919"},"PeriodicalIF":6.9,"publicationDate":"2026-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074759","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 : 2026-01-26DOI: 10.1016/j.applthermaleng.2026.129980
Qi-Hang Mei , Ji Chen , Jing-Yi Zhao , Xin Hou , Tian-Chun Dong , Shou-Hong Zhang , Yao-Jun Zhao , Lin Du
Two-phase closed thermosyphons (TPCTs) are widely used to stabilize permafrost subgrades, yet their long-term performance under sustained climatic warming remains poorly understood. This study leverages nearly two decades (2002−2020) of continuous field monitoring from three TPCT-reinforced subgrade sections along the Qinghai–Tibet Railway, including two sections in the Beiluhe Basin (BLH1 and BLH2) and one in the Kaixinling area (KXL), to provide robust, long-term evidence of permafrost thermal evolution and stabilization behavior under progressive degradation. The results show that TPCTs effectively improved the thermal stability of shallow permafrost, with the artificial permafrost table at the left shoulder of BLH1, BLH2, and KXL rising by 1.29 m, 0.77 m, and 1.27 m, respectively, accompanied by the cessation of ground settlement. However, deeper permafrost cooling was limited. When combined with crushed-rock revetments or insulation layers, TPCTs further improved overall thermal stability through enhanced ground–atmosphere heat exchange, demonstrating the benefits of integrated cooling measures. Nevertheless, at BLH1, the asymmetric TPCT layout reduced slope-related thermal imbalance but induced localized heat accumulation and increased cross-sectional differential deformation. At KXL, the cooling effect weakened after 2016, indicating potential limitations in the long-term sustainability of TPCT performance under a warming climate. These findings highlight the need for section-scale, site-adaptive TPCT designs that explicitly account for cross-sectional thermal interactions and potential attenuation of cooling performance under sustained climate warming. The results provide practical guidance for improving the long-term reliability of TPCT-based stabilization measures in permafrost engineering.
{"title":"Long-term cooling performance of two-phase closed thermosyphons in warming permafrost: a field case study from the Qinghai–Tibet railway","authors":"Qi-Hang Mei , Ji Chen , Jing-Yi Zhao , Xin Hou , Tian-Chun Dong , Shou-Hong Zhang , Yao-Jun Zhao , Lin Du","doi":"10.1016/j.applthermaleng.2026.129980","DOIUrl":"10.1016/j.applthermaleng.2026.129980","url":null,"abstract":"<div><div>Two-phase closed thermosyphons (TPCTs) are widely used to stabilize permafrost subgrades, yet their long-term performance under sustained climatic warming remains poorly understood. This study leverages nearly two decades (2002−2020) of continuous field monitoring from three TPCT-reinforced subgrade sections along the Qinghai–Tibet Railway, including two sections in the Beiluhe Basin (BLH1 and BLH2) and one in the Kaixinling area (KXL), to provide robust, long-term evidence of permafrost thermal evolution and stabilization behavior under progressive degradation. The results show that TPCTs effectively improved the thermal stability of shallow permafrost, with the artificial permafrost table at the left shoulder of BLH1, BLH2, and KXL rising by 1.29 m, 0.77 m, and 1.27 m, respectively, accompanied by the cessation of ground settlement. However, deeper permafrost cooling was limited. When combined with crushed-rock revetments or insulation layers, TPCTs further improved overall thermal stability through enhanced ground–atmosphere heat exchange, demonstrating the benefits of integrated cooling measures. Nevertheless, at BLH1, the asymmetric TPCT layout reduced slope-related thermal imbalance but induced localized heat accumulation and increased cross-sectional differential deformation. At KXL, the cooling effect weakened after 2016, indicating potential limitations in the long-term sustainability of TPCT performance under a warming climate. These findings highlight the need for section-scale, site-adaptive TPCT designs that explicitly account for cross-sectional thermal interactions and potential attenuation of cooling performance under sustained climate warming. The results provide practical guidance for improving the long-term reliability of TPCT-based stabilization measures in permafrost engineering.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"290 ","pages":"Article 129980"},"PeriodicalIF":6.9,"publicationDate":"2026-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146096123","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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