Microdroplets have an extremely wide range of applications in biomedical, chemical, and petroleum fields. A three-dimensional numerical model of a cross flow microchannel was developed using the OpenFOAM framework to investigate the dynamics and controlling factors of droplet generation. Four discrete flow regimes (slug, drip, jet, parallel flow) were identified within the ranges of 0 ≤ Cac ≤ 0.14 and 0 ≤ Cad ≤ 0.0014. Their formation is governed by either an extrusion or shear mechanism. Quantitative analysis revealed that elevating the continuous phase flow velocity or its dynamic viscosity significantly reduced droplet length by up to 78.86% and increased the droplet generation frequency by a factor of 11.5. Decreasing surface tension or increasing contact angle promoted droplet formation. Additionally, an increase in microchannel width was observed to cause a 113% increase in droplet length and a 17.5% reduction in generation frequency. Furthermore, a correlative model was developed to forecast the dimensionless droplet length, featuring a maximum error of ± 15%.
{"title":"Numerical investigation of droplet formation and regulation mechanisms in cross flow microchannels","authors":"Jiayi Wang, Shijia Cui, Jinlong Wang, Qiang Li, Weiwei Xu","doi":"10.1016/j.applthermaleng.2026.129863","DOIUrl":"10.1016/j.applthermaleng.2026.129863","url":null,"abstract":"<div><div>Microdroplets have an extremely wide range of applications in biomedical, chemical, and petroleum fields. A three-dimensional numerical model of a cross flow microchannel was developed using the OpenFOAM framework to investigate the dynamics and controlling factors of droplet generation. Four discrete flow regimes (slug, drip, jet, parallel flow) were identified within the ranges of 0 ≤ <em>Ca</em><sub><em>c</em></sub> ≤ 0.14 and 0 ≤ <em>Ca</em><sub><em>d</em></sub> ≤ 0.0014. Their formation is governed by either an extrusion or shear mechanism. Quantitative analysis revealed that elevating the continuous phase flow velocity or its dynamic viscosity significantly reduced droplet length by up to 78.86% and increased the droplet generation frequency by a factor of 11.5. Decreasing surface tension or increasing contact angle promoted droplet formation. Additionally, an increase in microchannel width was observed to cause a 113% increase in droplet length and a 17.5% reduction in generation frequency. Furthermore, a correlative model was developed to forecast the dimensionless droplet length, featuring a maximum error of ± 15%.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129863"},"PeriodicalIF":6.9,"publicationDate":"2026-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146024194","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 : 2026-01-21DOI: 10.1016/j.applthermaleng.2026.129885
Kangning Xiong , Qingsong Pan , Yang Liu , Yi Wang , Haijun Chen
Building energy consumption and greenhouse gas emissions are significant challenges facing the global building systems. Heat pipe technology has gained attention in energy efficiency for buildings due to its excellent heat transfer performance. Research advancements encompassed the fields of solar water heating systems, HVAC systems, and building envelopes. In solar water heating systems, optimizing thermal efficiency was a priority. In HVAC systems, improving the COP and optimizing dehumidification capabilities were important indicators. In building envelopes, heat pipes achieved energy savings through solar radiation and embedded designs. Current research shows that heat pipes can improve the system’s heat collection efficiency and COP value, and reduce building heat loss, but they face challenges such as low-temperature freezing, load fluctuation adaptation, interface thermal resistance, cost, and maintenance. The proposed strategies mainly include optimizing the working fluid, improving the structural design, and integrating intelligent control. Future efforts need to focus on low-temperature adaptation, load adjustment, and full-life-cycle reliability to promote large-scale use of heat pipes in buildings. This review aims to provide reference guidance for the application and development of heat pipe technology in the building systems.
{"title":"Advances, challenges and strategies of heat pipe application and development in building systems","authors":"Kangning Xiong , Qingsong Pan , Yang Liu , Yi Wang , Haijun Chen","doi":"10.1016/j.applthermaleng.2026.129885","DOIUrl":"10.1016/j.applthermaleng.2026.129885","url":null,"abstract":"<div><div>Building energy consumption and greenhouse gas emissions are significant challenges facing the global building systems. Heat pipe technology has gained attention in energy efficiency for buildings due to its excellent heat transfer performance. Research advancements encompassed the fields of solar water heating systems, HVAC systems, and building envelopes. In solar water heating systems, optimizing thermal efficiency was a priority. In HVAC systems, improving the COP and optimizing dehumidification capabilities were important indicators. In building envelopes, heat pipes achieved energy savings through solar radiation and embedded designs. Current research shows that heat pipes can improve the system’s heat collection efficiency and COP value, and reduce building heat loss, but they face challenges such as low-temperature freezing, load fluctuation adaptation, interface thermal resistance, cost, and maintenance. The proposed strategies mainly include optimizing the working fluid, improving the structural design, and integrating intelligent control. Future efforts need to focus on low-temperature adaptation, load adjustment, and full-life-cycle reliability to promote large-scale use of heat pipes in buildings. This review aims to provide reference guidance for the application and development of heat pipe technology in the building systems.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129885"},"PeriodicalIF":6.9,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146024095","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 : 2026-01-21DOI: 10.1016/j.applthermaleng.2026.129880
Sathyasree Nirmala , P.M. Sutheesh , B. Rohinikumar
Effective thermal management is vital for maintaining the safety, efficiency, and longevity of high-power lithium-ion battery packs in electric vehicles (EVs). This study presents comprehensive numerical investigations on a novel Fibonacci finned battery thermal management system (BTMS) integrated with phase change material (PCM) for passive thermal regulation. A three-dimensional transient model based on the enthalpy-porosity method was developed to simulate coupled heat conduction, natural convection, and phase change processes. The proposed design was benchmarked against a conventional unfinned configuration through performance metrics such as maximum temperature and temperature difference of the pack and liquid fraction trends. Results indicate that Fibonacci finned BTMS markedly reduces peak cell temperature and enhances temperature uniformity, maintaining the maximum temperature within the safe operational limit even under 5C discharge. Reduction in peak temperature of 4.69 K and improvement in temperature uniformity up to 64.6 % were achieved with finned system at 5C discharge compared to unfinned system, confirming its superior thermal performance. Detailed parametric investigations were carried out considering fin material (copper, aluminium), PCM (1-tetradecanol, n-eicosane), and ambient temperature, under various discharges (1C-5C). Between PCMs, 1-tetradecanol minimized peak temperature, while n-eicosane offered better thermal uniformity, emphasizing a trade-off between cooling strength and heat-spreading ability. At elevated ambient temperatures (312.15 K), PCM effectiveness diminished due to complete melting, reducing latent heat absorption capacity. Copper fins provided slightly better heat dissipation than aluminium but incurred a 3.27-fold increase in fin mass, making aluminium a more practical choice. Overall, the Fibonacci finned PCM based BTMS demonstrates a lightweight, passive, and efficient solution for thermal regulation in high-power Li-ion battery systems. The study delivers valuable design insights for optimizing finned geometry and PCM selection to balance thermal performance, mass, efficiency, and operational safety in EV applications.
{"title":"Numerical investigations on thermal performance and parametric investigations of lithium-ion battery pack with Fibonacci finned phase change material","authors":"Sathyasree Nirmala , P.M. Sutheesh , B. Rohinikumar","doi":"10.1016/j.applthermaleng.2026.129880","DOIUrl":"10.1016/j.applthermaleng.2026.129880","url":null,"abstract":"<div><div>Effective thermal management is vital for maintaining the safety, efficiency, and longevity of high-power lithium-ion battery packs in electric vehicles (EVs). This study presents comprehensive numerical investigations on a novel Fibonacci finned battery thermal management system (BTMS) integrated with phase change material (PCM) for passive thermal regulation. A three-dimensional transient model based on the enthalpy-porosity method was developed to simulate coupled heat conduction, natural convection, and phase change processes. The proposed design was benchmarked against a conventional unfinned configuration through performance metrics such as maximum temperature and temperature difference of the pack and liquid fraction trends. Results indicate that Fibonacci finned BTMS markedly reduces peak cell temperature and enhances temperature uniformity, maintaining the maximum temperature within the safe operational limit even under 5C discharge. Reduction in peak temperature of 4.69 K and improvement in temperature uniformity up to 64.6 % were achieved with finned system at 5C discharge compared to unfinned system, confirming its superior thermal performance. Detailed parametric investigations were carried out considering fin material (copper, aluminium), PCM (1-tetradecanol, n-eicosane), and ambient temperature, under various discharges (1C-5C). Between PCMs, 1-tetradecanol minimized peak temperature, while n-eicosane offered better thermal uniformity, emphasizing a trade-off between cooling strength and heat-spreading ability. At elevated ambient temperatures (312.15 K), PCM effectiveness diminished due to complete melting, reducing latent heat absorption capacity. Copper fins provided slightly better heat dissipation than aluminium but incurred a 3.27-fold increase in fin mass, making aluminium a more practical choice. Overall, the Fibonacci finned PCM based BTMS demonstrates a lightweight, passive, and efficient solution for thermal regulation in high-power Li-ion battery systems. The study delivers valuable design insights for optimizing finned geometry and PCM selection to balance thermal performance, mass, efficiency, and operational safety in EV applications.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129880"},"PeriodicalIF":6.9,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074437","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 : 2026-01-21DOI: 10.1016/j.applthermaleng.2026.129858
Kan Wang , Hanzhe Chen , Hao Wang , Xiaolei Liu , Rui Qiu
Thermos-hydrodynamic performance of marine fuel accidental ignition process is crucial for improving fire risk detection efficiency in ship industry. However, traditional numerical or experimental methods are computationally expensive and time inefficient. To address this, this study proposes a hybrid GWO-CNN-BiLSTM model, a novel approach for estimating initial ignition of marine fuel and real-time assessment. This model leverages grey wolf optimizer (GWO) algorithm to optimize the hyperparameters of a hybrid model that combines convolutional neural network (CNN) and bidirectional long short-term memory network (BiLSTM), enhancing multi-scale feature extraction and reducing overfitting. A ship motion-sloshing interactions-based experimental design is formulated, and thermos-hydrodynamic dataset is validated via ANSYS FLUENT simulations. The dataset concerning with marine fuel hot surface ignition is partitioned for model training and optimization within the proposed GWO-CNN-BiLSTM framework. For performance evaluation, the proposed model is quantitatively analyzed and benchmarked against two deep learning-based models: CNN-LSTM and CNN-LSTM. Results show that GWO-CNN-BiLSTM model outperforms all evaluation metrics in predicting thermal performance indicators of initial ignitions, with MAPE consistently remaining below 2.20% and MAE achieving merely 1.53 °C. The hybrid model proposed in current study exhibits superior prediction accuracy and generalization capability, demonstrating the strong potential for assessing initial ship fires in real-world applications.
{"title":"Thermo-informed hybrid deep learning model for transient indicator in marine fuel accidental ignition considering irregular ship motion","authors":"Kan Wang , Hanzhe Chen , Hao Wang , Xiaolei Liu , Rui Qiu","doi":"10.1016/j.applthermaleng.2026.129858","DOIUrl":"10.1016/j.applthermaleng.2026.129858","url":null,"abstract":"<div><div>Thermos-hydrodynamic performance of marine fuel accidental ignition process is crucial for improving fire risk detection efficiency in ship industry. However, traditional numerical or experimental methods are computationally expensive and time inefficient. To address this, this study proposes a hybrid GWO-CNN-BiLSTM model, a novel approach for estimating initial ignition of marine fuel and real-time assessment. This model leverages grey wolf optimizer (GWO) algorithm to optimize the hyperparameters of a hybrid model that combines convolutional neural network (CNN) and bidirectional long short-term memory network (BiLSTM), enhancing multi-scale feature extraction and reducing overfitting. A ship motion-sloshing interactions-based experimental design is formulated, and thermos-hydrodynamic dataset is validated via ANSYS FLUENT simulations. The dataset concerning with marine fuel hot surface ignition is partitioned for model training and optimization within the proposed GWO-CNN-BiLSTM framework. For performance evaluation, the proposed model is quantitatively analyzed and benchmarked against two deep learning-based models: CNN-LSTM and CNN-LSTM. Results show that GWO-CNN-BiLSTM model outperforms all evaluation metrics in predicting thermal performance indicators of initial ignitions, with MAPE consistently remaining below 2.20% and MAE achieving merely 1.53 °C. The hybrid model proposed in current study exhibits superior prediction accuracy and generalization capability, demonstrating the strong potential for assessing initial ship fires in real-world applications.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129858"},"PeriodicalIF":6.9,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074684","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}
Understanding the coupling between performance and heat release is crucial for the thermal management of rotating detonation engines (RDEs). This study experimentally investigates the performance and heat release characteristics of a two-phase rotating detonation combustor (RDC), focusing on the effects of the equivalence ratio (ER) and outlet area ratio (AR). Parameters such as RDW velocity (V), total pressure recovery (σ), combustion efficiency (ηc), and zonally resolved heat fluxes (qF, qB) are selected for analysis. The results demonstrate that AR is the dominant factor governing σ and the global flow structure, while ER primarily regulates the chemical energy input. During the detonation mode transition process, the changes in performance parameters such as thrust and chamber pressure show a certain degree of synchronization with the heat release characteristics. Based on the combustion structure of the internal flow of RDC, the RDC is divided into the front-end detonation section and the back-end deflagration section. It is found that the heat release at the front-end detonation section has a strong correlation with V, while the heat release at the back-end deflagration section has a closer relationship with ηc. This work provides essential data and proposes a novel zonally-resolved mechanistic model that correlates distinct heat release characteristics with specific performance parameters, offering a new framework to support the design of thermal prediction and management systems for RDEs.
{"title":"Experimental study on heat release characteristics and performance parameters of two-phase rotating detonation combustor under different equivalence ratios and outlet area ratios","authors":"Liming Liu, Jiaojiao Wang, Yun Wu, Feilong Song, Xin Chen, Jinhui Kang, Qi Chen","doi":"10.1016/j.applthermaleng.2026.129854","DOIUrl":"10.1016/j.applthermaleng.2026.129854","url":null,"abstract":"<div><div>Understanding the coupling between performance and heat release is crucial for the thermal management of rotating detonation engines (RDEs). This study experimentally investigates the performance and heat release characteristics of a two-phase rotating detonation combustor (RDC), focusing on the effects of the equivalence ratio (ER) and outlet area ratio (AR). Parameters such as RDW velocity (<em>V</em>), total pressure recovery (<em>σ</em>), combustion efficiency (<em>η</em><sub><em>c</em></sub>), and zonally resolved heat fluxes (<em>q</em><sub><em>F</em></sub>, <em>q</em><sub><em>B</em></sub>) are selected for analysis. The results demonstrate that AR is the dominant factor governing <em>σ</em> and the global flow structure, while ER primarily regulates the chemical energy input. During the detonation mode transition process, the changes in performance parameters such as thrust and chamber pressure show a certain degree of synchronization with the heat release characteristics. Based on the combustion structure of the internal flow of RDC, the RDC is divided into the front-end detonation section and the back-end deflagration section. It is found that the heat release at the front-end detonation section has a strong correlation with <em>V</em>, while the heat release at the back-end deflagration section has a closer relationship with <em>η</em><sub><em>c</em></sub>. This work provides essential data and proposes a novel zonally-resolved mechanistic model that correlates distinct heat release characteristics with specific performance parameters, offering a new framework to support the design of thermal prediction and management systems for RDEs.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129854"},"PeriodicalIF":6.9,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146024096","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 : 2026-01-21DOI: 10.1016/j.applthermaleng.2026.129846
Muyang Yu , Yiping Song , Chong Han , Musen Lin , Long Ni
Non-uniform distribution of gas-liquid refrigerant entering multi-circuit evaporators after throttling is a prevalent issue that significantly compromises efficiency. One effective solution to overcome this issue is to separate and bypass refrigerant gas to the outlet of the evaporators. Therefore, experiments were conducted to investigate the relationship between the effectiveness of gas-liquid separation, refrigerant distribution uniformity, and the performance of multi-circuit evaporators with gas bypass technology. Experimental results show that adjusting the bypass branch resistance is a key method for controlling gas separation efficiency under complete gas-liquid separation. Increasing the gas separation efficiency leads to significant improvements in the performance of multi-circuit evaporators, with maximum reductions of 70% in cooling capacity non-uniformity and 44% in evaporator pressure loss. Furthermore, the total superheat degree increases by 4.6 °C and 5.8 °C at total refrigerant flow rates of 60 kg/h and 80 kg/h, respectively, while decreasing by 0.4 °C at 40 kg/h. Without adjusting the bypass branch resistance, the difference in cooling capacity non-uniformity between gas bypass and conventional modes decreases with increasing quality at 60 kg/h and 80 kg/h. Particularly at 60 kg/h, the difference in total superheat degree between two modes initially increases before decreasing with rising quality, peaking around a quality of 0.18.
{"title":"Experimental investigation on distribution uniformity in multi-circuit evaporator with refrigerant gas separated and bypassed","authors":"Muyang Yu , Yiping Song , Chong Han , Musen Lin , Long Ni","doi":"10.1016/j.applthermaleng.2026.129846","DOIUrl":"10.1016/j.applthermaleng.2026.129846","url":null,"abstract":"<div><div>Non-uniform distribution of gas-liquid refrigerant entering multi-circuit evaporators after throttling is a prevalent issue that significantly compromises efficiency. One effective solution to overcome this issue is to separate and bypass refrigerant gas to the outlet of the evaporators. Therefore, experiments were conducted to investigate the relationship between the effectiveness of gas-liquid separation, refrigerant distribution uniformity, and the performance of multi-circuit evaporators with gas bypass technology. Experimental results show that adjusting the bypass branch resistance is a key method for controlling gas separation efficiency under complete gas-liquid separation. Increasing the gas separation efficiency leads to significant improvements in the performance of multi-circuit evaporators, with maximum reductions of 70% in cooling capacity non-uniformity and 44% in evaporator pressure loss. Furthermore, the total superheat degree increases by 4.6 °C and 5.8 °C at total refrigerant flow rates of 60 kg/h and 80 kg/h, respectively, while decreasing by 0.4 °C at 40 kg/h. Without adjusting the bypass branch resistance, the difference in cooling capacity non-uniformity between gas bypass and conventional modes decreases with increasing quality at 60 kg/h and 80 kg/h. Particularly at 60 kg/h, the difference in total superheat degree between two modes initially increases before decreasing with rising quality, peaking around a quality of 0.18.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129846"},"PeriodicalIF":6.9,"publicationDate":"2026-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146024135","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 : 2026-01-20DOI: 10.1016/j.applthermaleng.2026.129879
Yiyuan Qiao , Yifeng Hu , Yunho Hwang
When phase change materials (PCMs) are integrated with vapor compression cycle (VCC) condensers for thermal energy storage, system efficiency and reliability depend on both stable operation during the PCM phase transition and dynamic performance over the full operating cycle, as the PCM absorbs both sensible and latent heat. Although condenser subcooling strongly influences VCC performance and PCM melting behavior, systematic experimental investigations of this coupling remain limited. This study introduces the concept of a nominal subcooling degree (NSD), defined under steady-state refrigerant charge conditions, to evaluate subcooling effects in a PCM-integrated condenser. Experimental results indicate that the optimal NSD for steady-state operation is 5 K, resulting in a maximum coefficient of performance (COP) of 4.2. However, under long-duration operation, the optimal NSD shifts to 0.8 K. At NSD = 0.8 K, COP decreases by 31.3% between 0.5 h and 5.5 h, compared with a 44.2% reduction at NSD = 5 K. Higher NSDs are found to intensify non-uniform PCM melting and to accelerate performance degradation. These results reveal the dynamic coupling between refrigerant subcooling and the thermal behavior of the PCM, demonstrating that optimal subcooling depends on the operating duration. The findings provide practical guidance for subcooling management and system design, including the use of auxiliary subcoolers, to improve the efficiency and durability of PCM-integrated condenser systems.
{"title":"Optimal operation of phase change material integrated condenser under various subcooling conditions","authors":"Yiyuan Qiao , Yifeng Hu , Yunho Hwang","doi":"10.1016/j.applthermaleng.2026.129879","DOIUrl":"10.1016/j.applthermaleng.2026.129879","url":null,"abstract":"<div><div>When phase change materials (PCMs) are integrated with vapor compression cycle (VCC) condensers for thermal energy storage, system efficiency and reliability depend on both stable operation during the PCM phase transition and dynamic performance over the full operating cycle, as the PCM absorbs both sensible and latent heat. Although condenser subcooling strongly influences VCC performance and PCM melting behavior, systematic experimental investigations of this coupling remain limited. This study introduces the concept of a nominal subcooling degree (NSD), defined under steady-state refrigerant charge conditions, to evaluate subcooling effects in a PCM-integrated condenser. Experimental results indicate that the optimal NSD for steady-state operation is 5 K, resulting in a maximum coefficient of performance (COP) of 4.2. However, under long-duration operation, the optimal NSD shifts to 0.8 K. At NSD = 0.8 K, COP decreases by 31.3% between 0.5 h and 5.5 h, compared with a 44.2% reduction at NSD = 5 K. Higher NSDs are found to intensify non-uniform PCM melting and to accelerate performance degradation. These results reveal the dynamic coupling between refrigerant subcooling and the thermal behavior of the PCM, demonstrating that optimal subcooling depends on the operating duration. The findings provide practical guidance for subcooling management and system design, including the use of auxiliary subcoolers, to improve the efficiency and durability of PCM-integrated condenser systems.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129879"},"PeriodicalIF":6.9,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146024136","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 : 2026-01-20DOI: 10.1016/j.applthermaleng.2026.129873
Mohd Moiz , Amogh Shetty , Atul Srivastava
This study develops empirical correlations for bubble dynamic parameters for nucleate flow boiling. The key dynamic parameters include bubble equivalent and base diameters, upstream and downstream contact angles and aspect ratio. Unlike existing correlations that focus primarily on bubble lift-off, the correlations developed here are generalized in nature and enable the prediction of bubble dynamic parameters at any given time instant of the complete ebullition cycle (nucleation to lift-off) using high-speed imaging and advanced data processing. The experimental conditions encompass flow rate of 6–40 lph (Re = 720–4800), heat input in the range 24–47 W (heat flux: 27.4–53.7 kW/m2) and subcooling of 2–20 K, with data acquisition at normalized time intervals of 0–1. A novel approach leveraging the divergence theorem was applied to reconstruct 3D vapor bubbles obtained from 2D binary masks to estimate their volume for precise equivalent diameter measurement. Correlations were developed using five dimensionless parameters: Reynolds number (720–4800), subcooled Jakob number (6.04−61.15), boiling number (8.82E-5 – 4.45E-4), normalized time (0–1) and density ratio (5.96E-4 − 6.04E-4), thus avoiding any need of direct wall superheat measurements. Differential Evolution optimization algorithm was used to extract optimal coefficients for nonlinear empirical correlations from 4772 training data points, which were validated on 975 test samples. The correlations exhibited excellent predictive accuracy with average errors of 13.9% (equivalent diameter), 14.6% (base diameter), 9.8% (downstream contact angle), 9.6% (upstream contact angle), and 7.9% (aspect ratio). Comparison with existing correlations demonstrated superior generalization capability with significantly lower prediction errors across all parameters and better performance on independent datasets. The developed correlations provide a robust tool for predicting bubble dynamics throughout the bubble ebullition cycle, valuable for both experimental and numerical simulations in boiling heat transfer systems.
{"title":"Data-driven empirical correlation framework for full-cycle vapor bubble dynamics in nucleate flow boiling","authors":"Mohd Moiz , Amogh Shetty , Atul Srivastava","doi":"10.1016/j.applthermaleng.2026.129873","DOIUrl":"10.1016/j.applthermaleng.2026.129873","url":null,"abstract":"<div><div>This study develops empirical correlations for bubble dynamic parameters for nucleate flow boiling. The key dynamic parameters include bubble equivalent and base diameters, upstream and downstream contact angles and aspect ratio. Unlike existing correlations that focus primarily on bubble lift-off, the correlations developed here are generalized in nature and enable the prediction of bubble dynamic parameters at any given time instant of the complete ebullition cycle (nucleation to lift-off) using high-speed imaging and advanced data processing. The experimental conditions encompass flow rate of 6–40 lph (<em>Re</em> = 720–4800), heat input in the range 24–47 W (heat flux: 27.4–53.7 kW/m<sup>2</sup>) and subcooling of 2–20 K, with data acquisition at normalized time intervals of 0–1. A novel approach leveraging the divergence theorem was applied to reconstruct 3D vapor bubbles obtained from 2D binary masks to estimate their volume for precise equivalent diameter measurement. Correlations were developed using five dimensionless parameters: Reynolds number (720–4800), subcooled Jakob number (6.04−61.15), boiling number (8.82E-5 – 4.45E-4), normalized time (0–1) and density ratio (5.96E-4 − 6.04E-4), thus avoiding any need of direct wall superheat measurements. Differential Evolution optimization algorithm was used to extract optimal coefficients for nonlinear empirical correlations from 4772 training data points, which were validated on 975 test samples. The correlations exhibited excellent predictive accuracy with average errors of 13.9% (equivalent diameter), 14.6% (base diameter), 9.8% (downstream contact angle), 9.6% (upstream contact angle), and 7.9% (aspect ratio). Comparison with existing correlations demonstrated superior generalization capability with significantly lower prediction errors across all parameters and better performance on independent datasets. The developed correlations provide a robust tool for predicting bubble dynamics throughout the bubble ebullition cycle, valuable for both experimental and numerical simulations in boiling heat transfer systems.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129873"},"PeriodicalIF":6.9,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074444","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 : 2026-01-20DOI: 10.1016/j.applthermaleng.2026.129883
Helong Jin , Xiaohui Bai , Xianlong Meng , Cunliang Liu
The suction side of adjustable turbine guide vanes in variable cycle engines experiences significant aerodynamic variations under different turning angles, which strongly influence the coolant attachment behavior. However, the adverse effects induced by turning angle variation and their underlying mechanisms have not been systematically investigated. To address this issue, this study integrates pressure-sensitive paint experiments with validated simulations to systematically investigate the suction side film cooling behavior under varying turning angles, relative mass flow ratios, and density ratios, and further evaluates structural modifications. Experimental and numerical results indicate that decreasing turning angles intensifies the suction side pressure gradient and strengthens the passage vortex, thereby affecting coolant attachment and film coverage. Specifically, reducing turning angles further deteriorates performance, with surface-averaged film cooling effectiveness reduced by 5.1–6.7% and relative standard deviation increased by 8.3–14.6% compared to the design setting. Furthermore, increasing coolant mass flow enhances near-hole cooling performance but leads to more concentrated coolant coverage. A higher density ratio is found to improve front-region attachment and increases surface-averaged film cooling effectiveness by 14.1–21.7%, though at expense of downstream uniformity. Structural modifications featuring smaller holes and staggered layouts further expand the coverage area and raise surface-averaged film cooling effectiveness by 7.0–8.7%, but still cause a deterioration in uniformity. These results provide a reference for the thermal-protection design of adjustable turbine guide vanes in next-generation variable cycle engines.
{"title":"Experimental study on suction side film cooling characteristics of an adjustable turbine guide vane under different turning angles for a variable cycle engine","authors":"Helong Jin , Xiaohui Bai , Xianlong Meng , Cunliang Liu","doi":"10.1016/j.applthermaleng.2026.129883","DOIUrl":"10.1016/j.applthermaleng.2026.129883","url":null,"abstract":"<div><div>The suction side of adjustable turbine guide vanes in variable cycle engines experiences significant aerodynamic variations under different turning angles, which strongly influence the coolant attachment behavior. However, the adverse effects induced by turning angle variation and their underlying mechanisms have not been systematically investigated. To address this issue, this study integrates pressure-sensitive paint experiments with validated simulations to systematically investigate the suction side film cooling behavior under varying turning angles, relative mass flow ratios, and density ratios, and further evaluates structural modifications. Experimental and numerical results indicate that decreasing turning angles intensifies the suction side pressure gradient and strengthens the passage vortex, thereby affecting coolant attachment and film coverage. Specifically, reducing turning angles further deteriorates performance, with surface-averaged film cooling effectiveness reduced by 5.1–6.7% and relative standard deviation increased by 8.3–14.6% compared to the design setting. Furthermore, increasing coolant mass flow enhances near-hole cooling performance but leads to more concentrated coolant coverage. A higher density ratio is found to improve front-region attachment and increases surface-averaged film cooling effectiveness by 14.1–21.7%, though at expense of downstream uniformity. Structural modifications featuring smaller holes and staggered layouts further expand the coverage area and raise surface-averaged film cooling effectiveness by 7.0–8.7%, but still cause a deterioration in uniformity. These results provide a reference for the thermal-protection design of adjustable turbine guide vanes in next-generation variable cycle engines.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"290 ","pages":"Article 129883"},"PeriodicalIF":6.9,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146096152","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 : 2026-01-20DOI: 10.1016/j.applthermaleng.2026.129772
Ayaz Mehmood, Mohammad Zunaid, Ashok Kumar Madan
Cold spray (CS) has wide applications in surface engineering for the production of dense, well-bonded, and low-oxidation coatings. This study presents a multi-objective optimization (MOO) of the high-pressure cold spray (HPCS) process, which combines CFD simulations with Face-Centered Central Composite Design (FCCD), Response Surface Methodology (RSM), and the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The determination of the best compromise solutions was performed using multi-criteria decision-making (MCDM) analysis through the application of TOPSIS and VIKOR methods with hybrid AHP-EWM weighting. Key operating and design parameters considered as input variables in the optimization were gas pressure (), gas temperature (), particle diameter (), throat diameter (), and standoff distance (SoD), with particle velocity (PV), particle temperature (PT), and radial dispersion (RD) as the desired responses in copper (Cu) deposition on an aluminum (Al) substrate. The performance of the RSM models showed high predictive accuracy (R2 > 0.94), with residual values within the range of ±3.6218. The sensitivity analysis revealed that and were the most significant parameters affecting PV and PT, while had a significant effect on RD. The optimized conditions yielded higher PV, controlled PT, and reduced RD compared with the reference case, using a Rosin-Rammler particle size distribution of 2–75 μm. Such results provide a strategic framework to improve coating quality, bonding, and deposition efficiency in CS deposition.
{"title":"CFD-based multi-objective optimization of cold spray parameters for enhanced coating quality and minimized radial dispersion","authors":"Ayaz Mehmood, Mohammad Zunaid, Ashok Kumar Madan","doi":"10.1016/j.applthermaleng.2026.129772","DOIUrl":"10.1016/j.applthermaleng.2026.129772","url":null,"abstract":"<div><div>Cold spray (CS) has wide applications in surface engineering for the production of dense, well-bonded, and low-oxidation coatings. This study presents a multi-objective optimization (MOO) of the high-pressure cold spray (HPCS) process, which combines CFD simulations with Face-Centered Central Composite Design (FCCD), Response Surface Methodology (RSM), and the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The determination of the best compromise solutions was performed using multi-criteria decision-making (MCDM) analysis through the application of TOPSIS and VIKOR methods with hybrid AHP-EWM weighting. Key operating and design parameters considered as input variables in the optimization were gas pressure (<span><math><mrow><msub><mi>G</mi><mi>p</mi></msub></mrow></math></span>), gas temperature (<span><math><mrow><msub><mi>G</mi><mi>t</mi></msub></mrow></math></span>), particle diameter (<span><math><mrow><msub><mi>D</mi><mi>p</mi></msub></mrow></math></span>), throat diameter (<span><math><mrow><msub><mi>D</mi><mi>t</mi></msub></mrow></math></span>), and standoff distance (SoD), with particle velocity (PV), particle temperature (PT), and radial dispersion (RD) as the desired responses in copper (Cu) deposition on an aluminum (Al) substrate. The performance of the RSM models showed high predictive accuracy (R<sup>2</sup> > 0.94), with residual values within the range of ±3.6218. The sensitivity analysis revealed that <span><math><mrow><msub><mi>D</mi><mi>p</mi></msub></mrow></math></span> and <span><math><mrow><msub><mi>G</mi><mi>t</mi></msub></mrow></math></span> were the most significant parameters affecting PV and PT, while <span><math><mrow><msub><mi>D</mi><mi>t</mi></msub></mrow></math></span> had a significant effect on RD. The optimized conditions yielded higher PV, controlled PT, and reduced RD compared with the reference case, using a Rosin-Rammler particle size distribution of 2–75 μm. Such results provide a strategic framework to improve coating quality, bonding, and deposition efficiency in CS deposition.</div></div>","PeriodicalId":8201,"journal":{"name":"Applied Thermal Engineering","volume":"289 ","pages":"Article 129772"},"PeriodicalIF":6.9,"publicationDate":"2026-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074374","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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