International Journal of Heat and Mass Transfer最新文献_第10页

Investigation of thermoacoustic heat dissipation characteristics with various gases in a self-excited travelling-standing wave acoustic field 自激行驻波声场中不同气体的热声散热特性研究

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128132

Mingyang Sun , Siqin Hou , Cheng Zhang , Lei Jiang , Guoqing Shen , Haisheng Chen

Thermoacoustic technology is environmentally friendly, reliable and flexible. The generation of thermoacoustic effect is accompanied by thermoacoustic oscillatory convection which is significantly different from the conventional heat transfer method. It provides a new idea for thermal management and thermal energy application: thermoacoustic heat dissipation. In this study, combining experimental data and artificial neural network, the heat transfer enhancement power of thermoacoustic oscillatory convection is obtained with self-excited travelling-standing wave acoustic field. The highest enhancement power of helium, nitrogen and argon are 1945 W, 885 W and 808 W, respectively. Meanwhile, the pressure is shown to be directly proportional to the enhancement of the heat transfer effect of the thermoacoustic oscillation. For investigating the main factor affecting the heat transfer enhancement, the pressure amplitude, volumetric flow rate amplitude and impedance phase are analyzed in combination with experiments and simulations. It is found that the volumetric flow rate amplitude is the main factor affecting the heat transfer effect with various average pressures. The higher volumetric flow rate amplitude makes the gas parcels in the regenerator obtain a larger displacement amplitude, which means the gas experiences a higher wall temperature gradient during the movement. It also enhances the convective heat transfer coefficient in the heat exchanger and strengthens the effect of oscillatory heat transfer. In contrast, the pressure amplitude and impedance phase have a relatively small effect.

热声技术环保、可靠、灵活。热声效应的产生伴随着热声振荡对流，这与传统的换热方法有很大的不同。它为热管理和热能应用提供了新的思路：热声散热。本研究将实验数据与人工神经网络相结合，得到了自激行驻波声场下热声振荡对流的换热增强功率。氦气、氮气和氩气的最大增强功率分别为1945 W、885 W和808 W。同时，压力与热声振荡传热效果的增强成正比。为了研究影响传热强化的主要因素，结合实验和仿真分析了压力幅值、体积流量幅值和阻抗相位。研究发现，在不同平均压力下，体积流量幅值是影响换热效果的主要因素。体积流速幅值越大，蓄热器内气包的位移幅值越大，这意味着气体在运动过程中经历了较大的壁面温度梯度。它还提高了换热器内的对流换热系数，加强了振荡换热效果。相反，压力幅值和阻抗相位的影响相对较小。

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引用次数: 0

Modeling of gas transport in liquid water filled PEMFC gas diffusion layer facilitated by X-ray CT imaging 基于x射线CT成像的液态水填充PEMFC气体扩散层气体输运模拟

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128149

Hang Liu , Xuecheng Lv , Heng Huang , Yang Li , Zhifu Zhou , Wei-Tao Wu , Lei Wei , Jizu Lyu , Yubai Li , Yongchen Song

Mass transport polarization induced by water blockage within the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs) constitutes a critical bottleneck limiting high-current-density performance. This study establishes a model of water invasion under compression and thickness changes, facilitated by in-situ X-ray computed tomography (X-CT) imaging and finite element modeling based on realistic geometric structures. Subsequently, it investigates the gas transport under liquid saturation. Extraction of the pore network model (PNM) reveals that both compression and water flooding significantly reduce the mean pore diameter, while exerting minimal impact on the coordination number. The results indicate that liquid water transport pathways exhibit scale-dependent characteristics. Furthermore, the effective diffusion coefficient (EDC) and permeability (K) vary linearly with thickness. Notably, 40 % compression causes an 80 % reduction in permeability, while significantly mitigating the pressure drop phenomenon. This work provides multiscale insights into mass transport limitations across various porous media.

质子交换膜燃料电池（pemfc）气体扩散层（GDL）内水堵塞引起的质量输运极化是制约其高电流密度性能的关键瓶颈。本研究利用X-CT原位成像技术和基于真实几何结构的有限元建模技术，建立了压缩和厚度变化条件下的水侵模型。然后，研究了液体饱和条件下的气体输运。孔隙网络模型（PNM）的提取表明，压缩和水驱均能显著减小平均孔径，而对配位数的影响最小。结果表明，液态水输运路径具有尺度依赖特征。有效扩散系数（EDC）和渗透率(K)随厚度呈线性变化。值得注意的是，40%的压缩导致渗透率降低80%，同时显著缓解了压降现象。这项工作提供了跨各种多孔介质的质量传输限制的多尺度见解。

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引用次数: 0

Co-enhancement on heat conduction and specific surface area of copper benzene-1,3,5-tricarboxylate (Cu-BTC) MOF with addition of graphene oxide 氧化石墨烯对苯-1,3,5-三羧酸铜（Cu-BTC） MOF热传导和比表面积的共增强作用

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128147

Wantong Wang , Shun Liu , Jiayi Li , Yimei Zhang , Xiaoze Du

The classical metal-organic framework (MOF) Cu-BTC exhibits low thermal conductivity, which causes extreme temperature distribution inhomogeneity and limits its application as a support for methanol and steam reforming (MSR) thermocatalysts. A series of GO+Cu-BTC composites were synthesized via a one-pot hydrothermal method by combining Cu-BTC with graphene oxide (GO). The effects of GO with different oxidation degrees and mass fractions on the thermal conductivity from room temperature to 200 °C and the specific surface area of the composites were analyzed comprehensively, as well as the influence mechanism of GO addition on the thermal conductivity. The results indicated that the GO-induced changes in crystals characteristics, the formation of thermal conduction pathways through GO coverage and the new spaces between GO and Cu-BTC collectively achieve the co-enhancement on thermal conductivity and specific surface area and of the composites. For the composite with the same GO mass fraction, the thermal conductivity decreased with the increasing oxidation degree of GO and for the composite with the same GO oxidation degree, the thermal conductivity firstly decreased and then increased with the increasing mass fraction of GO. The specific surface area decreases with the increasing oxidation degree of GO and the optimum oxidation degree was 0.3. GO shows a significant enhancement in specific surface area at low mass fraction but caused a sharp decrease in specific surface area with the excessive GO mass fraction. Among all the composites, the optimal 0.1 wt.%GO-0.3+Cu-BTC exhibited the highest BET and Langmuir specific surface areas of 1394.55 m²/g and 1939.67 m²/g, which were 44 % and 43 % higher than those of pure Cu-BTC and its thermal conductivity at 25 °C, 100 °C and 200 °C achieved 0.31 W/(m· °C), 0.27 W/(m· °C) and 0.31 W/(m· °C), which were 211 %, 200 % and 53 % higher than that of pure Cu-BTC, respectively. It providing novel design strategies and experimental supports for the optimization of the heat transfer performance of MOFs developed as carriers for thermal catalytic systems.

经典金属有机骨架（MOF） Cu-BTC具有较低的导热系数，导致温度分布极不均匀，限制了其作为甲醇和蒸汽重整（MSR）热催化剂载体的应用。将Cu-BTC与氧化石墨烯（GO）结合，采用一锅水热法制备了一系列GO+Cu-BTC复合材料。综合分析了不同氧化程度和质量分数的氧化石墨烯对室温~ 200℃范围内复合材料导热系数和比表面积的影响，以及氧化石墨烯添加量对导热系数的影响机理。结果表明，氧化石墨烯引起的晶体特性变化、氧化石墨烯覆盖形成的热传导通道以及氧化石墨烯与Cu-BTC之间的新空间共同实现了复合材料导热系数和比表面积的增强。对于相同氧化石墨烯质量分数的复合材料，其导热系数随氧化石墨烯氧化程度的增加而降低；对于相同氧化石墨烯氧化程度的复合材料，其导热系数随氧化石墨烯质量分数的增加先降低后升高。氧化石墨烯的比表面积随着氧化程度的增加而减小，最佳氧化程度为0.3。在低质量分数下，氧化石墨烯的比表面积显著增强，但随着氧化石墨烯质量分数的增加，比表面积急剧下降。在所有复合材料中，0.1 wt.%GO-0.3+Cu-BTC的BET和Langmuir比表面积最高，分别为1394.55 m2/g和1939.67 m2/g，分别比纯Cu-BTC高44%和43%；其在25°C、100°C和200°C时的导热系数分别为0.31 W/（m·°C）、0.27 W/（m·°C）和0.31 W/(m·°C)，分别比纯Cu-BTC高211%、200%和53%。它为mof作为热催化系统载体的传热性能优化提供了新的设计策略和实验支持。

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引用次数: 0

Thermal behavior, fluid dynamics, and solidification characteristics within molten pool during pulse waveform shaping laser directed energy deposition 脉冲波形整形激光定向能沉积过程中熔池内的热行为、流体动力学和凝固特性

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128137

Zhenggang Chen , Jiazhu Wu , Gui Wang , Zuguo Liu , Min Hu , Hongwei Zhang , Jie Xiao

A three-dimensional thermo-fluid-metallurgical integrated model was developed for pulse waveform shaping laser directed energy deposition (PWS-LDED) under atmospheric conditions, incorporating the effects of surface-active elements (oxygen and sulfur) on molten pool surface tension. The model was employed to systematically investigate the influence of rectangular, ramp, triangular, and sinusoidal waves on thermal behavior, fluid dynamics, and solidification characteristics during deposition. The results show that all four pulse waveforms periodically modulate the temperature field and Marangoni convection through temporal energy distribution. The rectangular wave induces the most intense temperature fluctuations, with heat transfer alternating between convection-dominated and conduction-dominated regimes. In contrast, the sinusoidal wave exhibits minimal temperature oscillations but achieves the highest peak temperature due to significant heat accumulation. Under the combined influence of oxygen and sulfur, a positive surface tension gradient drives inward Marangoni flow across all waveforms. The sinusoidal wave generates the maximum peak flow velocity, while the rectangular wave shows the most pronounced velocity fluctuations. Regarding solidification behavior, the rectangular wave's stepwise heat input triggers the most significant columnar-to-equiaxed transition (CET) and produces the finest grains during laser-off periods. The ramp wave's linearly increasing heat input suppresses CET, resulting in progressive grain coarsening within single-pulse cycles. Both triangular and sinusoidal waves, with their symmetric rising/falling thermal profiles, inhibit CET during heating stages but promote CET during cooling stages, leading to graded microstructures with finer grains at pulse initiation/termination and coarser grains in intermediate regions. Among all waveforms, the sinusoidal wave yields the smallest fluctuation in grain size.

考虑表面活性元素（氧和硫）对熔池表面张力的影响，建立了大气条件下脉冲波形成形激光定向能沉积（PWS-LDED）的三维热流-冶金一体化模型。利用该模型系统地研究了矩形波、斜波、三角形波和正弦波对沉积过程中热行为、流体动力学和凝固特性的影响。结果表明，四种脉冲波形均通过时间能量分布周期性地调制温度场和马兰戈尼对流。矩形波引起最强烈的温度波动，传热在对流主导和传导主导之间交替进行。相反，正弦波表现出最小的温度振荡，但由于显着的热量积累而达到最高的峰值温度。在氧和硫的共同作用下，正表面张力梯度驱动所有波形的马兰戈尼流向内流动。正弦波产生的流速峰值最大，而矩形波的流速波动最明显。在凝固行为方面，矩形波的逐步热输入触发了最显著的柱向等轴转变（CET），并在激光关闭期间产生了最细的晶粒。斜坡波线性增加的热输入抑制了CET，导致单脉冲周期内晶粒逐渐粗化。三角波和正弦波都具有对称的上升/下降热分布，在加热阶段抑制热激振荡，但在冷却阶段促进热激振荡，导致脉冲起始/终止时晶粒更细，中间区域晶粒更粗的梯度组织。在所有波形中，正弦波产生的晶粒尺寸波动最小。

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引用次数: 0

Slug flow condensation identification with acoustic signatures 基于声学特征的段塞流冷凝识别

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128144

Lida Yan , Dylan Wallen , Ahmed Allam , Han Hu , Kishan Bellur , Ying Sun

Flow condensation offers efficient heat transfer but may suffer from performance degradation due to flow regime transitions. These transitions are difficult to characterize in real-world applications, particularly in internal flow condensation due to limited thermofluidic measurements and lack of direct visualization. This study introduces a non-destructive approach for slug flow condensation regime identification using acoustic emission (AE) signals. Experiments were conducted using a vertical downflow condensation setup with normal perfluorohexane (npfh) as working fluid and water as cooling fluid. The AE sensor is mounted on the outer enclosure. A parametric study was conducted over target inlet vapor qualities of 0.6–1.15 and vapor mass velocities of 116–419 kg/m²s, and the resulting acoustic signals were analyzed in both frequency and time domains. Results show a strong positive correlation between acoustic power and vapor mass velocity, with Pearson correlation coefficients of 0.71–0.91. There also exists a weak positive correlation between acoustic power and inlet vapor quality, with the coefficients of 0.02–0.22 across the frequency range. In addition, a novel method for identifying slug flow condensation is developed based on the probability density function (PDF) of acoustic absolute energy (E_Abs) using a two-component Gaussian Mixture Model (GMM). Slug flow was found to occur when there is bimodal distribution in the PDF of E_Abs, due to the strong periodicity in the E_Abs. The significant difference in the Bayesian Information Criterion (BIC) between the one- and two-component GMMs confirms that the model is not overfitted, demonstrating the robustness of the identified bimodal distribution. This method was verified by the pressure drop and acoustic wave propagation analysis based on two accelerometers. The results show that the PDF of E_Abs provides a robust, non-destructive, and non-optical approach for identifying slug flow condensation in acoustic-based flow regime characterization.

流动冷凝提供了有效的传热，但可能遭受性能下降，由于流动状态的转变。这些转变在实际应用中很难表征，特别是在内部流动冷凝中，由于有限的热流体测量和缺乏直接可视化。本文介绍了一种利用声发射（AE）信号进行段塞流凝聚态识别的非破坏性方法。实验采用垂直下流冷凝装置，以正常全氟己烷（npfh）为工质，水为冷却液。声发射传感器安装在外壳上。在目标入口蒸汽质量为0.6 ~ 1.15、蒸汽质量速度为116 ~ 419 kg/m²s的条件下进行了参数化研究，并对得到的声信号进行了频域和时域分析。结果表明，声功率与水汽质量速度呈正相关，Pearson相关系数为0.71 ~ 0.91。声功率与进口蒸汽质量之间也存在微弱的正相关关系，在整个频率范围内的系数为0.02 ~ 0.22。此外，利用双分量高斯混合模型（GMM），基于声绝对能（EAbs）的概率密度函数（PDF），提出了一种识别段塞流凝聚的新方法。由于EAbs具有很强的周期性，当EAbs的PDF呈双峰分布时，会产生段塞流。单分量和双分量GMMs之间贝叶斯信息准则（BIC）的显著差异证实了模型没有过拟合，证明了识别的双峰分布的鲁棒性。基于两个加速度计的压降和声波传播分析验证了该方法的有效性。结果表明，在基于声学的流态表征中，EAbs的PDF提供了一种鲁棒性、非破坏性和非光学的方法来识别段塞流凝结。

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引用次数: 0

Aerothermal performance of impinging jets onto concave effusion wall of rotating channels without and with crossed elliptical pedestal 无交叉椭圆基座和带交叉椭圆基座旋转通道凹壁面射流冲击的气动热性能

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128139

Shyy Woei Chang , Po Ning Huang

The heat transfer, pressure-drop, and aerothermal performances of three impinging jet-rows onto the concave effusion wall in two rotating channels without and with the crossed elliptical pedestals (CEPs) at an orientation angle of 20° are assessed by comparing their full-field Nusselt number (Nu) distributions, Fanning friction factors (f), and aerothermal performance indices (API). The channel Reynolds numbers (Re), rotation numbers (Ro), density ratios (Δρ/ρ), and buoyancy numbers (Bu) fall in the ranges of 7500–18,000, 0–0.75, 0.44–0.58, and 0.0441–1.51 respectively. Cooling attributes to CEPs promote overall heat transfer rates by maximum 34 % from the smooth-walled references in most rotating test conditions. As Ro increases, the Coriolis force-effect decoupled from the buoyancy- and inertial-force effects keeps raising the Nusselt number on trailing wall (TE); but causes an initial heat transfer elevation on leading wall (LE), which is following by a subsequent decline. Given the variety of Ro-driven heat transfer variations reported to date, the present study verifies that the density ratio and Reynolds number are the primary factors attributing to the dissimilar varying patterns. With the adverse buoyancy effect to deteriorate heat transfer performance in both rotating channels, the modified near-wall flows in the presence of Coriolis and inertial forces have led to the interdependency of Bu effect on Ro and Re, unveiling weakened buoyancy effect by increasing Ro and, or, Re. The underling flow mechanisms pertinent to impinging jets, effusion, and, or, CEPs significantly improve the aerothermal performances from the Dittus-Boelter and Blasius referenced scenarios, raising API to 1.66–2.83 and 1.9–2.89 for the rotating channels without and with CEPs respectively. Operating conditions with high Ro and large Δρ/ρ leverage the aerothermal improvements caused by CEPs, which upraise API by 30 % from those without CEP.

通过比较两种旋转通道内的努塞尔数（Nu）分布、范宁摩擦系数(f)和气动性能指数（API），对两种旋转通道内不带交叉椭圆基座（cep）和带交叉椭圆基座（cep）的三列射流在凹型积液壁上的传热、压降和气动热性能进行了评价。通道雷诺数Re、旋转数Ro、密度比Δρ/ρ和浮力数Bu分别为7500 ~ 18000、0 ~ 0.75、0.44 ~ 0.58和0.0441 ~ 1.51。在大多数旋转测试条件下，cep的冷却特性使整体换热率比光滑壁基准最高提高34%。随着Ro的增大，与浮力和惯性力效应解耦的科里奥利力效应使后壁面上的努塞尔数（TE）不断增大；但在导壁上引起初始传热标高（LE），随后下降。考虑到迄今为止报道的各种不同的ro驱动传热变化，本研究验证了密度比和雷诺数是导致不同变化模式的主要因素。由于不利的浮力效应会恶化两个旋转通道的传热性能，在科氏力和惯性力的作用下，改进的近壁流动导致了Bu效应对Ro和Re的相互依赖，通过增加Ro和Re来揭示浮力效应的减弱。与撞击射流、积液和cceps相关的潜在流动机制显著改善了Dittus-Boelter和Blasius参考情景的气动热性能。无cep旋转通道和有cep旋转通道的API分别提高到1.66-2.83和1.9-2.89。高Ro和大Δρ/ρ的操作条件利用CEP引起的空气热改善，使API比没有CEP的情况提高30%。

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引用次数: 0

Concept of a simple conductive thermal transistor based on an oxide phase change material 基于氧化物相变材料的简单导电热晶体管的概念

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128085

Cagatay Haratoka, Karl Joulain, Younès Ezzahri

We theoretically investigate the behaviors of the main features of a simple conductive thermal transistor (CTT) concept. The two operating modes, amplification and switching, of the CTT are achieved using a solid oxide phase change material (PCM) that shows a metal–insulator transition and examined in detail by individually changing various parameters. We model the CTT by exploiting the properties of one of the promising PCMs, which is

{VO}_{2}

. We found that the ratio of the thermal conductances between the states of the PCM and the stiffness of the phase transition greatly affect the amplification. Modifying the stiffness of the phase transition also allows modifying the operating temperature range of the amplification mode to some extent. Besides, we observed that depending on the temperatures of the collector, the emitter and the phase transition temperature of the PCM, a bistability regime occurs and this allows the CTT to operate in the switch mode. Therefore, the CTT can operate in both amplification and switch modes depending on the temperatures of its three elements (collector, base and emitter). The CTT provides the highest amplification before it transitions to the switch mode. Conversely, its switching efficiency decreases to the lowest value before it transitions to the amplification mode. Moreover, we derived analytical expressions, which are generally applicable to a CTT similar to the one we investigate in this study and its base element consists of solid-oxide PCMs showing similar phase transition characteristics with

{VO}_{2}

, to determine the base temperature resulting in the highest amplification factor and calculate the maximum amplification factor. We analytically demonstrate that the base temperature that induces the highest amplification factor is always less than the phase transition temperature, but lies in its vicinity.

我们从理论上研究了简单导电热晶体管（CTT）概念的主要特征的行为。CTT的放大和开关两种工作模式是使用固体氧化物相变材料（PCM）实现的，该材料显示金属-绝缘体转变，并通过单独改变各种参数来详细检查。我们通过利用一种有前途的pcm的特性来建模CTT，即VO2。我们发现相变材料状态之间的热导比和相变刚度对放大有很大的影响。修改相变的刚度也允许在一定程度上修改放大模式的工作温度范围。此外，我们观察到，根据集电极、发射极和PCM相变温度的不同，会出现双稳定状态，这使得CTT可以在开关模式下工作。因此，CTT可以在放大和开关模式下工作，这取决于它的三个元件（集电极、基极和发射极）的温度。CTT在转换到开关模式之前提供最高的放大。相反，在转换到放大模式之前，其开关效率下降到最低值。此外，我们推导出了一般适用于与本研究相似的CTT的解析表达式，该CTT的基元由与VO2具有相似相变特性的固体氧化物PCMs组成，用于确定导致最高放大因子的基温并计算最大放大因子。分析表明，引起最大放大系数的基温总是小于相变温度，但在其附近。

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引用次数: 0

Motion and rupture properties of droplets on inclined surfaces under ultrasonic excitation 超声激励下倾斜表面液滴的运动和破裂特性

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128108

Xin Wu, Jianying Gong, Yutao Wang, Xiangyu Li, Xiaolong Yang

In this paper, an active anti-frosting method based on ultrasonic driving droplets is proposed. The dynamic behaviors of droplets, including asymmetric spreading, directional motion and rupture, are systematically examined on inclined surfaces under 35 kHz ultrasonic excitation, with controlled variations in droplet volume, vibration velocity, and surface inclination angle. The results reveal that droplets exhibit pronounced asymmetric deformation and directional motion toward the pressure antinode, eventually stopping due to the resistance effect of the reversed acoustic radiation force. A dual-peak evolution in contact angle hysteresis is observed, where the first peak transitions from negative to positive with increasing surface inclination, highlighting the competing influences of gravity and ultrasonic wave on morphological control. Furthermore, the acoustic radiation force is quantitatively characterized through both Newton's second law and the acoustic radiation pressure integration model. Theoretical and experimental results exhibit good agreement in the overall trend, while their deviation attributed to droplet asymmetry, is found to correlate linearly with a proposed composite dimensionless number. Additionally, the formation of satellite droplets is captured and classified into four stages: stretching, necking, rupture, and retraction. Satellite droplets typically emerge within a narrow dimensionless time of 0.6∼0.8 and account for <0.5 % of the main droplet volume. A zonal rupture map is established based on the proposed dimensionless number, which enables effective classification of satellite-free droplet, critical satellite droplet, and satellite droplet regions. This work can provide data basis and technical support for optimizing active anti-frosting technologies by controllable liquid transport.

提出了一种基于超声驱动液滴的主动防霜方法。在35 kHz超声激励下，控制液滴体积、振动速度和表面倾角的变化，系统地研究了液滴在倾斜表面上的不对称扩散、定向运动和破裂等动力学行为。结果表明，液滴表现出明显的不对称变形和定向运动，最终由于反向声辐射力的阻力作用而停止。观察到接触角迟滞的双峰演化，其中第一个峰随着表面倾角的增加从负向正转变，突出了重力和超声波对形态控制的竞争影响。此外，通过牛顿第二定律和声辐射压力积分模型对声辐射力进行了定量表征。理论和实验结果在总体趋势上表现出良好的一致性，而由于液滴不对称引起的偏差与所提出的复合无因次数呈线性相关。此外，卫星液滴的形成被捕获并分为四个阶段：拉伸、颈缩、破裂和收缩。卫星液滴通常在0.6 ~ 0.8的无量纲时间内出现，占主要液滴体积的0.5%。基于所提出的无量纲数，建立了区域破裂图，实现了无卫星液滴、关键卫星液滴和卫星液滴区域的有效分类。本研究可为优化可控液体输送主动防霜技术提供数据依据和技术支持。

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引用次数: 0

How internal fins enhance the thermohydraulic performance of geothermal pipes: A direct numerical simulation study 内翅片如何增强地热管道的热水力性能：直接数值模拟研究

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128114

Niklas Hidman , Daniel Almgren , Kim Johansson , Eskil Nilsson

Geothermal heat exchanger systems provide stable, efficient, and sustainable heating and cooling solutions. Their performance can be enhanced by achieving more effective convective heat transfer in the collector pipes without causing excessive pressure drop. This study investigates the use of internal fins in pipes as a means to improve the thermohydraulic performance under operating conditions typical of geothermal applications (Reynolds numbers

1300 \leq Re \leq 3300

and Prandtl numbers

20 \leq \Pr \leq 75

). Direct numerical simulations are employed to examine three fin configurations: straight axial fins, continuous helical fins, and fins with alternating helical orientations along the pipe axis. The alternating helical fin design is shown to trigger an unsteady flow at significantly lower

Re

than the other designs. Using the alternating design, we analyse the influence of the fin height, number of fins and fin twist rate on the thermohydraulic performance. The results demonstrate that the proposed alternating helical configuration triggers unsteady flow down to

1700 < Re < 1800

while maintaining nearly the same friction factor as a smooth pipe at both

Re \leq 1700

and

Re \geq 2300

. The augmented flow gives 3–6 times higher heat transfer compared to a smooth pipe in the interval

1700 < Re < 2300

. The findings highlight a promising fin design strategy for geothermal systems where minimizing pressure losses is essential, and they facilitate general guidelines for developing efficient fin-enhanced heat exchanger pipes in related applications operating under similar conditions.

地热换热器系统提供稳定、高效、可持续的供暖和制冷解决方案。通过在集热器管道中实现更有效的对流换热而不会造成过大的压降，可以提高集热器的性能。本研究探讨了在地热应用的典型工况（雷诺数1300≤Re≤3300，普朗特数20≤Pr≤75）下，管道内翅片作为改善热工性能的一种手段。采用直接数值模拟的方法对三种翅片构型进行了研究：直线型轴向翅片、连续螺旋翅片和沿管轴方向螺旋方向交替的翅片。结果表明，与其他设计相比，交替螺旋翅片设计在显著降低Re时触发非定常流动。采用交替设计，分析了翅片高度、翅片数量和翅片捻度对热工性能的影响。结果表明，在Re≤1700和Re≥2300时，交替螺旋结构触发非定常流动至1700<；Re<1800，同时保持与光滑管道几乎相同的摩擦因数。在1700<；Re<；2300区间内，与光滑管道相比，增强流的换热量增加了3-6倍。这一发现强调了地热系统中翅片设计策略的前景，在地热系统中，最大限度地减少压力损失是必不可少的，它们为在类似条件下运行的相关应用中开发高效的翅片增强型热交换器管道提供了一般指导。

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引用次数: 0

Heat flux reconstruction in droplet impact experiments using infrared thermography through sapphire 利用蓝宝石红外热像仪重建液滴撞击实验中的热流密度

IF 5.8 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2025-11-24 DOI: 10.1016/j.ijheatmasstransfer.2025.128069

T. Potaufeux , O. Caballina , T. Czerwiec , G. Castanet

Accurate reconstruction of heat flux during droplet impact is achieved using infrared thermography through a sapphire substrate coated with a thin emissive layer. This requires accounting for the sapphire’s intrinsic thermal emission and radiative absorption, particularly below 300 °C, as filtering wavelengths above 3.5 µm significantly reduces the signal available for high-resolution surface temperature measurements. Simple strategies, such as subtracting the signal of a bare sapphire or estimating the sapphire and coating emission after multiple internal reflections, can partially improve accuracy. However, their effectiveness depends on the coating’s emissivity and can lead to overestimation of sapphire emission for long droplet residence times. A more reliable approach couples heat conduction with a radiative model, efficiently implemented via the thermal quadrupole method combined with a sine-mode decomposition. With minimal iterations and few discretization points, the proposed method accurately reconstructs surface temperature and heat flux, rigorously correcting for sapphire self-emission and absorption, while remaining computationally efficient and straightforward to implement. A substantial improvement in accuracy, by several tens of percent, is observed for the reconstructed heat flux.

利用红外热成像技术，通过涂有薄发射层的蓝宝石衬底，实现了液滴撞击过程中热通量的精确重建。这需要考虑蓝宝石的固有热发射和辐射吸收，特别是在300°C以下，因为过滤波长高于3.5µm会显著降低高分辨率表面温度测量的信号。简单的策略，如减去裸蓝宝石的信号或估计多次内部反射后的蓝宝石和涂层发射，可以部分提高精度。然而，它们的有效性取决于涂层的发射率，并且可能导致对长液滴停留时间的蓝宝石发射的高估。一种更可靠的方法是将热传导与辐射模型相结合，通过结合正弦模式分解的热四极杆方法有效地实现。该方法迭代次数少，离散点少，能准确地重建表面温度和热通量，严格校正蓝宝石的自发射和吸收，同时计算效率高，易于实现。重建热通量的精度有了大幅度的提高，提高了几十个百分点。

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引用次数: 0