International Journal of Heat and Mass Transfer最新文献

{"title":"Comparative evaluation of battery charging strategies: Thermal behavior and charging performance","authors":"Xiaoqi Zeng ,&nbsp;Taotao Li ,&nbsp;Huirou Zhang ,&nbsp;Long Chen ,&nbsp;Jingwen Weng ,&nbsp;You Lv ,&nbsp;Weixiong Wu","doi":"10.1016/j.ijheatmasstransfer.2025.127947","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127947","url":null,"abstract":"<div><div>As a core energy storage component in renewable energy systems, lithium-ion batteries face critical challenges in balancing charging performance with thermal safety. While existing studies have explored conventional charging strategies, systematic experimental comparisons under varying ambient temperatures remain limited. This study presents a comprehensive experimental investigation into the thermal-electrical coupling effects of seven advanced charging strategies, including constant current (CC), multi-stage constant current (MCC), changed multi-stage constant current (CMCC), boost charging (BC), constant power charging (CPC), positive pulse charging (PPC), and positive-negative pulse charging (PNPC), across a wide ambient temperature range (15 °C to 45 °C). The results indicated that BC demonstrated superior performance in terms of thermal uniformity and temperature fluctuation control. Compared to the other charging strategies, BC reduced the maximum temperature rise at the center of the battery surface during charging by up to 39.62 % and improved energy efficiency by as much as 3.74 %, making it particularly suitable for applications with stringent requirements on charging rate and temperature control. Moreover, it was found that the critical ambient temperature range for enhancing energy efficiency was between 25 °C and 45 °C. Additionally, the charging times of BC and CPC were highly sensitive to ambient temperature, suggesting that temperature should be carefully considered when optimizing these two charging strategies. This study provides theoretical support for tailoring charging strategies for lithium-ion batteries in various application scenarios. Moreover, it offers valuable reference for the research and optimization of fast-charging strategies.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127947"},"PeriodicalIF":5.8,"publicationDate":"2025-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145264305","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}

{"title":"Range improvement in BEV trucks using heat pump for cabin heating instead of PTC heater","authors":"Taha Erkin Tunalı,&nbsp;Elif Gözen,&nbsp;Emre Özgül","doi":"10.1016/j.ijheatmasstransfer.2025.127910","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127910","url":null,"abstract":"<div><div>The Paris Agreement (2016) and the European Green Deal (2018) have accelerated the development of zero-emission technologies in the transportation sector, particularly for heavy-duty vehicles. Battery electric vehicles (BEVs), while offering promising emission reductions, suffer from range limitations under cold ambient conditions due to the significant energy demand for cabin heating. This study investigates the performance of a heat pump system as an alternative to the conventional Positive Temperature Coefficient (PTC) heater in a heavy-duty electric truck application. A detailed one-dimensional (1D) vehicle thermal model is developed using GT-Suite to simulate the dynamic behavior of a 16-ton BEV truck equipped with a 300 kWh battery pack. The simulation is conducted under 0 °C ambient conditions using the On-Road Fuel Economy driving cycle. Compared to the PTC heater configuration, the heat pump system achieved a 31.64% reduction in auxiliary thermal energy consumption, resulting in a 1.18% improvement in overall battery energy consumption. These improvements translate into a measurable increase in driving range under cold climate scenarios. This study demonstrates the feasibility and effectiveness of integrating heat pump systems in heavy-duty electric trucks, which has not been extensively covered in previous literature focused primarily on passenger vehicles. While numerous studies have explored EV thermal management using various simulation platforms, including widely adopted tools like MATLAB/Simulink and Modelica, a comprehensive investigation specifically for heavy-duty BEV trucks, particularly focusing on the detailed 1D thermal modeling approach adopted here, remains less common.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127910"},"PeriodicalIF":5.8,"publicationDate":"2025-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145326218","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}

{"title":"Experimental Nusselt number correlations for heat transfer of a single spherical particle in turbulent flow","authors":"Huina Guo ,&nbsp;Xinde Zhang ,&nbsp;Lele Feng ,&nbsp;Yuanyi Wu ,&nbsp;Yuxin Wu","doi":"10.1016/j.ijheatmasstransfer.2025.127939","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127939","url":null,"abstract":"<div><div>Gas-solid heat transfer is crucial in industrial reactors. The classic Ranz-Marshall correlation works well under low turbulence intensity but underestimates the Nusselt number <em>Nu</em> when turbulent fluctuations match or exceed the mean flow. This study delves into the heat transfer of a single spherical particle in turbulent flows through extensive experiments and develops unified Nusselt number correlations. A custom-designed four-fan turbulent heating setup is employed to create homogeneous and isotropic turbulence region (<em>u</em>_rms ≤ 4.18 m/s, integral length scale <em>L</em> ≈ 14 mm), effectively isolating the pure turbulent effect. By conducting heating experiments on a single copper sphere at different furnace temperatures and turbulent fluctuation velocities, and employing the lumped-parameter method to measure particle temperature, the Nusselt number is inversely determined via a zero-dimensional energy balance model. The results indicate a sub-linear relationship between the Nusselt number and the particle turbulent Reynolds number <em>Re</em>_t. An improved correlation for pure turbulent environments is derived from experimental data, as <span><math><mrow><mi>N</mi><mi>u</mi><mspace></mspace><mrow><mo>=</mo><mspace></mspace><mn>2</mn><mo>+</mo><mn>0</mn></mrow><mrow><mo>.</mo><mn>6</mn></mrow><mi>R</mi><msubsup><mi>e</mi><mrow><mi>t</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msubsup><mi>P</mi><msup><mi>r</mi><mrow><mn>1</mn><mo>/</mo><mn>3</mn></mrow></msup><msup><mrow><mo>(</mo><mrow><mi>C</mi><mo>/</mo><mi>d</mi></mrow><mo>)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mn>5</mn></mrow></msup><msup><mrow><mo>(</mo><mrow><msub><mi>T</mi><mi>f</mi></msub><mo>/</mo><msub><mi>T</mi><mi>p</mi></msub></mrow><mo>)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mn>5</mn></mrow></msup></mrow></math></span>. Furthermore, a coupled correlation considering both mean flow and turbulent fluctuation is proposed, capable of seamlessly transitioning between mean flow-dominated and turbulence-dominated regimes via a nonlinear composite formulation. Comparisons with the references validates the proposed correlations with an acceptable error of 10 % over a wide Reynolds range. This research highlights the significant role of turbulent fluctuations in enhancing heat transfer under high turbulence intensity. The developed correlations provide a more accurate tool for predicting <em>Nu</em> in complex gas-solid flows, aiding in understanding and modeling heat and mass transfer processes in turbulent multiphase flows, and offering critical guidance for subsequent reaction processes in industrial combustors.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127939"},"PeriodicalIF":5.8,"publicationDate":"2025-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145322005","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}

{"title":"Mechanical behavior and properties of gas diffusion layer in proton exchange membrane fuel cells at subzero temperatures","authors":"Fei Jia ,&nbsp;Shuwei Song ,&nbsp;Guoxu Zhang ,&nbsp;Ming Chen ,&nbsp;Chengpeng Yang","doi":"10.1016/j.ijheatmasstransfer.2025.127934","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127934","url":null,"abstract":"<div><div>Ice formation in proton exchange membrane fuel cells under subfreezing conditions affects mass and heat transfer in components, causing significant degradation in cell performance and a reduction in cell durability. In this study, the X-ray CT test is conducted, and the microstructure of the gas diffusion layer (GDL) is analyzed and reconstructed. The experimental results show that the porosity distribution of gas diffusion layer is uneven through the thickness direction. Then, the three-dimensional model is established by considering heat transfer, phase change, and mechanical response. The mechanical behavior of gas diffusion layer and the critical transport parameters at subzero temperatures are investigated. The modeling results indicate that the magnitude of displacement decreases with ice content but increases with assembly pressure. At a high ice content and low clamping pressure, the displacement distribution tends to be more uniform. Moreover, with the combined effect of ice formation and clamping pressure in the gas diffusion layer, both the porosity and effective diffusion coefficient show pronounced declining variations with compression ratio, leading to higher mass transfer resistance and severe performance degradation. However, the effective thermal conductivity increases with the compression ratio, indicating the positive effect on heat transfer and more even temperature distribution in gas diffusion layer. These results reveal the profound effect of ice on the transport properties of gas diffusion layer and could be capable of providing a basis for obtaining accurate behavior of the cell.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127934"},"PeriodicalIF":5.8,"publicationDate":"2025-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145322006","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}

{"title":"Synergistic enhancement of flow boiling heat transfer by composite structure and gradient wettability","authors":"Kaiyu Tan ,&nbsp;Yurong He ,&nbsp;Yanwei Hu ,&nbsp;Jiaqi Zhu","doi":"10.1016/j.ijheatmasstransfer.2025.127888","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127888","url":null,"abstract":"<div><div>Microchannel flow boiling heat transfer has garnered significant attention in heat dissipation applications owing to its exceptional heat transfer capacity and compact configuration. However, microscale confinement effects often induce bubble blockage, leading to critical thermal issues such as localized dry-out, non-uniform wall temperature distribution, and vapor backflow, ultimately constraining improvements in heat transfer efficiency. The present work performs a systematic numerical investigation to explore two-phase flow behaviors within microchannels featuring innovative structural configurations and surface wettability modifications. We propose a composite microchannel design characterized by a radial gradient wettability, comprising an upper superhydrophobic region and a lower superhydrophilic region. Results revealed two distinct enhancement mechanisms: a cyclic rewetting mechanism induced by the superhydrophobic upper region, substantially improving thermal performance within the bubbly flow region by promoting liquid replenishment; and a vapor radial extraction mechanism resulting from synergistic structural and wettability interactions, effectively mitigating bubble blockage in the lower region. This dual mechanism notably suppressed localized dry-out and enhanced overall heat transfer performance. Comparative analyses against homogeneous wettability microchannels demonstrated that the gradient wettability composite structure achieved a maximum enhancement of 166.3 % in the Performance Evaluation Criterion, along with reductions of 64.2 % and 45.1 % in the average and exit bottom wall superheat, respectively, alongside improved temperature uniformity. These findings substantiate the significant potential of synergistic structural and wettability modifications for enhancing two-phase flow boiling performance, offering essential insights for advancing microchannel heat dissipation technologies.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127888"},"PeriodicalIF":5.8,"publicationDate":"2025-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145322009","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}

{"title":"An analytical/numerical evaporation model for an oscillating spheroidal droplet in a potential flow","authors":"Y. Hu,&nbsp;S. Tonini,&nbsp;G.E. Cossali","doi":"10.1016/j.ijheatmasstransfer.2025.127925","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127925","url":null,"abstract":"<div><div>An analytical/numerical model for the evaporation of an oscillating droplet is proposed, by solving the species conservation equation in the gas phase in a generalized spheroidal coordinate system. The quasi-steady assumption is released, and the effect of the moving interface on the droplet evaporation is discussed. The evaporation characteristic of an oscillating droplet differs from that under quasi-steady conditions. The differences in evaporation flux vary <span><math><mrow><mo>−</mo><mn>12</mn><mo>.</mo><mn>5</mn><mtext>%</mtext><mo>∼</mo><mn>12</mn><mo>.</mo><mn>7</mn><mtext>%</mtext></mrow></math></span> at the poles, and <span><math><mrow><mo>−</mo><mn>6</mn><mo>.</mo><mn>0</mn><mtext>%</mtext><mo>∼</mo><mn>6</mn><mo>.</mo><mn>6</mn><mtext>%</mtext></mrow></math></span> at the equator for an initial aspect ratio of 1.2. This difference leads to the evaporation rate and oscillation being out of phase, although having the same frequency. The amplitude of the evaporation rate depends on the initial droplet deformation, whether the droplet shape is prolate or oblate. The mass loss of the droplet within one period rises, as the initial droplet deformation increases. Different evaporating conditions have a slight effect on the evaporation characteristic.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127925"},"PeriodicalIF":5.8,"publicationDate":"2025-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145264375","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}

{"title":"Experimental and theoretical analysis of a spontaneous Leidenfrost transitioning phenomenon","authors":"H. Yang ,&nbsp;P. Valluri ,&nbsp;K. Sefiane","doi":"10.1016/j.ijheatmasstransfer.2025.127941","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127941","url":null,"abstract":"<div><div>This study offers a thorough experimental and theoretical analysis of a unique droplet behavior known as spontaneous Leidenfrost transitioning (SLT). This phenomenon occurs between stable transitional boiling and Leidenfrost rebound. By creating a novel experimental platform that allows for spatial observations of hydrodynamic and thermodynamic behaviors, we uncover significant insights into SLT. Our experimental observations indicate that the occurrence of SLT is independent of the Bond number. However, a higher temperature is necessary to trigger SLT as the Bond number increases. Initially, SLT expands but narrows with rising Weber number, with larger Bond numbers exhibiting earlier narrowing due to intensified thermal-induced instability. Furthermore, enhanced surface smoothness and hydrophilicity are unfavorable for SLT initiation. We identify three distinct phases of SLT: intensive boiling, consecutive levitation, and stable Leidenfrost rebound. By analyzing three hydrodynamic parameters during the second phase, we propose a mechanism describing the evolution of SLT at increasing temperatures. Our investigations into phase transitions reveal that rapid retraction and the formation of a central lift force drive the transition from intensive boiling to consecutive levitation. We also establish a theoretical model to describe the subsequent transition into stable Leidenfrost rebound, which validates the case-sensitive nature of the proposed mechanism while successfully linking it to droplet deformation and heat transfer behavior. These findings provide valuable insights into the underexplored droplet behaviors between two well-known regimes, enhancing the understanding of transitional boiling instability and the transition from stable transitional boiling to Leidenfrost rebound.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127941"},"PeriodicalIF":5.8,"publicationDate":"2025-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145322008","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}

{"title":"Multi-scale modelling on the dynamic microstructure evolution and solute segregation behavior for the adjustable-ring-mode (ARM) laser welding on Al-Mg-Si alloy","authors":"Xiaoying Liu ,&nbsp;Chendong Shao ,&nbsp;Xiaojian Xu ,&nbsp;Yaqi Wang ,&nbsp;Yunfei Meng ,&nbsp;Fenggui Lu","doi":"10.1016/j.ijheatmasstransfer.2025.127913","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127913","url":null,"abstract":"<div><div>To address the issue of how the special energy field affects solidification microstructure evolution and solute segregation for the novel ARM laser welding on Al-Mg-Si alloy, a macro-micro coupling multi-scale numerical model was built in this paper. As comparison, under the condition of pure core laser welding, the fundamental reason for formation of coarse columnar crystals with 586.37 μm width was that high and rapidly changing temperature gradient <em>G</em> and pulling velocity <em>R</em> inhibited the undercooling zone expansion, resulting in insufficient driving force for grain nucleation and then the promotion of rapid columnar crystal growth. A small average primary dendritic arm spacing (PDAS) of 4.1 μm was generated. However, under the condition of ARM laser welding, the significant reduction of nearly 50 % in <em>G</em> and <em>R</em> and their gently changing trends allowed the undercooling zone to expand, promoting the grain nucleation, inhibiting the columnar crystal growth by about 19.7 %, and increasing the average PDAS by 21.9 %. Further, adopting the ring beam weakened the solute micro-segregation and regional segregation. The slower cooling rate and thicker undercooling layer made the solute have more time and space for sufficient diffusion, reducing enrichment concentration from approximately 6 % to 4 %. And the uniform energy distribution in the molten pool ensured that solute diffusion behavior did not change significantly during the solidification process, with the average solute concentration variation shifting from an increase of 0.9 % to 1.4 % to a slight fluctuation around 1 %.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127913"},"PeriodicalIF":5.8,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145264304","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}

{"title":"Enhanced pool boiling of HFE7100 on gallium-based liquid metal surfaces: Role of flexibility and nanoparticle modification","authors":"Lu Liu ,&nbsp;Kai Bi ,&nbsp;Xilin Wang ,&nbsp;Teng Wang ,&nbsp;Xinyu Dong","doi":"10.1016/j.ijheatmasstransfer.2025.127929","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127929","url":null,"abstract":"<div><div>This study experimentally investigates pool boiling heat transfer of HFE7100 on gallium-based liquid metal surfaces, including: pure liquid gallium, Ga-In-Sn alloy, and nanoparticle-modified Ga-In-Sn alloy. Employing a visualization setup, the effects of surface flexibility, roughness, and wettability on pool boiling and bubble dynamics were analyzed. Results show that liquid metals significantly reduce wall superheat at the onset of nucleate boiling (ONB). Pure liquid gallium exhibits the lowest superheat (3.51 K), achieving a 61.25 % reduction compared to copper. High-speed imaging reveals that capillary-driven flexible deformation generates dynamic wrinkles and cavity-bridging phenomena, accelerating bubble departure. Pure liquid gallium exhibits superior bubble departure frequency and higher heat transfer coefficient relative to Ga-In-Sn alloy, due to the fact that the surface of pure liquid gallium is more prone to fluctuations. Nanoparticle-modified Ga-In-Sn alloy achieves the highest critical heat flux (CHF) which is 67.71 % higher than copper, because nanoparticle modification enhances hydrophilicity and increases roughness, inhibiting the formation of vapor film. This work demonstrates the potential of liquid metals in thermal management and provides an innovative approach to utilizing surface flexibility to promote pool boiling.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127929"},"PeriodicalIF":5.8,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145264377","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}

{"title":"Experimental and numerical studies on the forced and mixed convections of water in eccentric micro annular channels","authors":"Yang Yang ,&nbsp;Xiaofeng Yuan ,&nbsp;Zhijun Li","doi":"10.1016/j.ijheatmasstransfer.2025.127931","DOIUrl":"10.1016/j.ijheatmasstransfer.2025.127931","url":null,"abstract":"<div><div>Microchannels are frequently employed to enhance heat transfer in the compact and highly efficient heat transfer devices. However, studies on the smooth eccentric micro annular channel remain scarce. The flow and heat transfer performance of horizontal eccentric micro annular channels with a hydraulic diameter of 6.0 mm and an eccentricity of 0.5–1.5 mm subjected to constant heat flux are investigated using experimental and numerical methods. For laminar and turbulent flows, the laminar model and the realizable k-ε model with the Menter-Lechner near-wall treatment in Fluent are adopted, respectively. Results indicate that the critical Reynolds number for laminar-to-turbulent transition is 992. The friction factor, Nusselt number and entropy generation are significantly influenced by the operational and structure parameters. The Nusselt number under forced laminar flow conditions exhibits turbulent-like characteristics. The critical buoyancy number for forced-to-mixed convection transition decreases with increasing the eccentricity: for laminar flow, the values are 0.0107, 0.0082, and 0.0035 at the eccentricities of 0.5 mm, 1.0 mm, and 1.5 mm, respectively; for turbulent flow, the values are 0.0099, 0.0092, and 0.0026 at the same eccentricities. Compared to the forced convection, the buoyancy force enhances the Nusselt number and reduces the entropy generation, while the friction factor remains independent of the buoyancy force. Finally, the correlations for the friction factor and Nusselt number under both the laminar and turbulent flow regimes are proposed.</div></div>","PeriodicalId":336,"journal":{"name":"International Journal of Heat and Mass Transfer","volume":"256 ","pages":"Article 127931"},"PeriodicalIF":5.8,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145264301","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}