International Journal of Heat and Mass Transfer最新文献_第3页

Thermoelastic damping in moderately thick microplate resonators based on the fractional heat conduction model 基于分数热传导模型的中等厚度微板谐振器中的热弹性阻尼

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-12 DOI: 10.1016/j.ijheatmasstransfer.2024.126394

Ya-Wei Wang, Xue-Yang Zhang, Xian-Fang Li

Thermoelastic damping is a fundamental mechanism for intrinsic energy loss in resonators operating at room temperature. Accurate prediction of thermoelastic damping is of paramount importance for the design and manufacture of high-performance micro-resonators. In this study, thermoelastic dissipation in relatively thick micro-plate resonators is investigated. A new first-order shear deformation plate theory, or the simplified Mindlin plate theory (SMPT), and fractional-order Fourier heat conduction are utilized to establish an analytical model for thermoelastic micro-plates. By employing the complex frequency approach (CFA) and energy ratio approach (ERA), an analytical expression for the inverse quality factor

Q^{- 1}

of rectangular micro-plates is derived. To validate the present model, the numerical results for fully clamped thin plates and SMPT are compared, and those for fully simply supported thick plates using CFA and ERA are also compared. Emphasis is focused on analyzing the effects of shear deformation and rotary inertia of the section, subdiffusion, normal diffusion, and superdiffusion on thermoelastic damping in moderately thick micro-plate resonators. The effect of geometry, vibration modes, boundary constraints, and ambient temperatures on thermoelastic dissipation is also discussed. The numerical results indicate that shear deformation should be considered while the rotary inertia may be neglected in the analysis of thermoelastic damping in vibrating relatively thick plates for the fundamental mode.

热弹性阻尼是共振器在室温下工作时产生内在能量损失的基本机制。准确预测热弹性阻尼对于设计和制造高性能微型谐振器至关重要。本研究对相对较厚的微板谐振器中的热弹性耗散进行了研究。利用新的一阶剪切变形板理论（或简化明德林板理论（SMPT））和分数阶傅里叶热传导建立了热弹性微板的分析模型。通过采用复频方法（CFA）和能量比方法（ERA），得出了矩形微板反品质因数 Q-1 的分析表达式。为了验证本模型，比较了完全夹紧薄板和 SMPT 的数值结果，还比较了使用 CFA 和 ERA 的完全简支撑厚板的数值结果。重点分析了剪切变形和截面旋转惯性、次扩散、法向扩散和超扩散对中等厚度微板谐振器热弹性阻尼的影响。此外，还讨论了几何形状、振动模式、边界约束和环境温度对热弹性耗散的影响。数值结果表明，在分析振动相对较厚的板的基本模式的热弹性阻尼时，应考虑剪切变形，同时可忽略旋转惯性。

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引用次数: 0

Numerical investigation on aerothermal performances of film cooled high pressure turbine vane under inlet non-uniformities 入口不均匀条件下薄膜冷却高压涡轮叶片气热性能的数值研究

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-12 DOI: 10.1016/j.ijheatmasstransfer.2024.126398

Shenghui Zhang , Shuiting Ding , Tian Qiu , Chuangkai Liu , Chenyu Gan

Lean-premixed combustion technologies have been widely adopted in advanced civil turbofan engine to reduce NOx emission. There exist hot streak (HS) and swirl simultaneously at the exit of lean-premixed combustor. Current paper presents a numerical investigation on the aerothermal performances of film cooled high pressure turbine (HPT) nozzle guide vane (NGV) subjected to HS and swirl. Current investigation was carried on the stage one film cooled NGV of GE-E3 HPT, which took into consideration the realistic clocking position of HPT NGV relative to the fuel injector in combustor. The effects of swirl orientations on the migration of HS and film coolant and the aerothermal performances on NGV surface were examined. Results demonstrates that, swirl and its induced incidence angle effect turn over some film coolant from pressure side (PS) to suction side (SS), or vice versa. Such effects also dominate the radial migration of film coolant. The redistributions of film coolant show significant effect on the film cooling effectiveness on NGV surface. Compared with no-swirl case, the greater film cooling effectiveness appears at the region where film coolant accumulates, and as expected, the smaller film cooling effectiveness arises at the region covered by less film coolant. As for heat transfer coefficient (HTC), swirl affects HTC on NGV surface mainly through redistributing film coolant and the hot fluid from HS. The migrations of film coolant and hot fluid keep step with each other on the NGV surfaces directly impinged by inlet HS and swirl, so that the HTC distributions on these surfaces are not significantly affected by swirl. The radial momentum of film coolant endowed by the film hole with radial incidence angle can partly offset the swirl's induced incidence angle effect, which reduces the variations in film cooling effectiveness and heat transfer coefficient due to swirl.

为减少氮氧化物的排放，先进的民用涡扇发动机广泛采用了贫油预混燃烧技术。贫油预混燃烧器出口处同时存在热条纹（HS）和漩涡。本文对薄膜冷却高压涡轮（HPT）喷嘴导叶（NGV）在热条纹和漩涡作用下的气动热性能进行了数值研究。本次研究针对 GE-E3 HPT 的一级薄膜冷却 NGV，考虑了 HPT NGV 相对于燃烧器中燃料喷射器的实际时钟位置。研究了漩涡方向对 HS 和薄膜冷却剂迁移的影响以及 NGV 表面的气热性能。结果表明，漩涡及其诱导的入射角效应会使一些薄膜冷却剂从压力侧（PS）转向吸气侧（SS），反之亦然。这种效应还主导着冷却液薄膜的径向迁移。薄膜冷却剂的重新分布对 NGV 表面的薄膜冷却效果有显著影响。与无漩涡情况相比，在薄膜冷却剂聚集的区域，薄膜冷却效果较强，而在薄膜冷却剂覆盖较少的区域，薄膜冷却效果较弱。至于传热系数（HTC），漩涡主要通过重新分配膜冷却剂和来自 HS 的热流体来影响 NGV 表面的 HTC。在直接受到入口热交换器和漩涡冲击的 NGV 表面上，膜冷却剂和热流体的迁移保持同步，因此这些表面上的 HTC 分布不会受到漩涡的明显影响。具有径向入射角的膜孔赋予膜冷却剂的径向动量可以部分抵消漩涡的诱导入射角效应，从而减小漩涡对膜冷却效果和传热系数的影响。

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引用次数: 0

Thermo-hydrodynamic performance and geyser boiling flows of a novel co-axial condensing heat pipe (CCHP) for low-grade green energy exploitations 用于低品位绿色能源开发的新型同轴冷凝热管 (CCHP) 的热流体力学性能和喷泉沸腾流

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-12 DOI: 10.1016/j.ijheatmasstransfer.2024.126391

Yong-Juan Song , Bin Li , Jun-Hao Chen , Wei-Wei Wang , Fu-Yun Zhao , Jiang-Hua Guo

Due to their excellent heat transfer efficiency, two-phase closed thermosiphons (TPCTs) are essential for solar applications and the cooling of electronics. In this research, a novel coaxial condensing heat pipe (CCHP) was proposed, which has a more compact structure compared to traditional heat pipe, given the same volume and heat transfer area. Numerical modeling and experimental investigation were fully utilized to examine the influences of heat inputs, inclination angles, liquid filling ratios, and working mediums on the heat transmission properties of CCHP. The vapor-liquid flow phenomenon along with the thermal and mass transmission mechanism of CCHP under various operating conditions were explored. Our findings demonstrated that CCHP exhibited optimal thermal transmission performance at the tilt angle of 60° when the filling rate is 50 % and the input power is 100 W, the minimum thermal resistance of CCHP is 0.284K/W. At the tilt angle of 60° and input power of 100 W, CCHP has the lowest thermal resistance of 0.267K/W. Besides, the utilization of ethanol as a working medium could simultaneously reduce the evaporator temperature and enhance the thermal properties of CCHP. Inside CCHP, "geyser boiling" phenomena was further observed. Our experimental findings and numerical ones agreed well for each other. This innovative heat pipe could be confident and robust applied in the solar energy collection and relevant heat transfer enhancement fields.

由于具有出色的传热效率，两相封闭热虹吸管（TPCT）对于太阳能应用和电子设备冷却至关重要。本研究提出了一种新型同轴冷凝热管（CCHP），与传统热管相比，在相同体积和传热面积的情况下，其结构更为紧凑。研究充分利用数值建模和实验研究，考察了热输入、倾斜角、液体填充率和工作介质对 CCHP 传热性能的影响。研究还探讨了 CCHP 在不同工作条件下的汽液流动现象以及热传导和质量传输机制。研究结果表明，当填充率为 50%、输入功率为 100 W 时，CCHP 在倾斜角度为 60° 时具有最佳的热传导性能，其最小热阻为 0.284K/W。在倾斜角度为 60°、输入功率为 100 W 时，CCHP 的热阻最小，为 0.267K/W。此外，使用乙醇作为工作介质可同时降低蒸发器温度和提高 CCHP 的热性能。在 CCHP 内部还进一步观察到了 "喷泉沸腾 "现象。我们的实验结果与数值结果相互吻合。这种创新的热管可以在太阳能收集和相关传热增强领域得到可靠和稳健的应用。

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引用次数: 0

Microchannel heat sinks for hotspot thermal management: achieving minimal pressure drop and maximal thermal performance 用于热点热管理的微通道散热器：实现最小压降和最大热性能

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-09 DOI: 10.1016/j.ijheatmasstransfer.2024.126411

Biqi Cao , Zan Wu

In hotspot regions, where heat flux can reach several orders of magnitude higher than in surrounding area, managing hotspot temperatures becomes a prominent issue. This study introduces three innovative heat sink designs that effectively manage high temperatures in hotspot regions while minimizing power consumption. The hydraulic and thermal performances of these designs were evaluated numerically and compared with those of the conventional straight parallel microchannel (SPMC) heat sink and previous designs from the literature. By integrating pin-fins in hotspot regions and positioning the fluid inlet above the hotspot to leverage jet impingement, these designs significantly improved the heat transfer coefficient in hotspot areas. The MMC structure, featuring a manifold configuration, achieved an 81.4 % reduction in pressure drop compared to the SPMC design. The RMC structure demonstrated superior temperature uniformity. Additionally, the impact of the jet inlet angle on the hydraulic-thermal performance of the RMC heat sink was investigated. The AMC structure, which integrates the benefits of both RMC and MMC, achieved an impressive 87.9 % reduction in pressure drop compared to the SPMC design, underscoring its advanced performance.

在热点区域，热通量可能比周围区域高出几个数量级，因此管理热点区域的温度成为一个突出问题。本研究介绍了三种创新的散热片设计，可有效控制热点区域的高温，同时最大限度地降低功耗。我们对这些设计的水力和热力性能进行了数值评估，并将其与传统的直平行微通道（SPMC）散热器和以往文献中的设计进行了比较。通过在热点区域集成针状鳍片，并将流体入口置于热点上方以充分利用射流冲击，这些设计显著提高了热点区域的传热系数。与 SPMC 设计相比，采用歧管配置的 MMC 结构的压降降低了 81.4%。RMC 结构的温度均匀性更好。此外，还研究了射流入口角度对 RMC 散热器水热性能的影响。AMC 结构集成了 RMC 和 MMC 的优点，与 SPMC 设计相比，压降降低了 87.9%，令人印象深刻，彰显了其先进的性能。

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引用次数: 0

Experimental investigation of the performance of a phase change material thermal management module under vacuum and atmospheric pressure conditions 真空和大气压条件下相变材料热管理模块性能的实验研究

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-08 DOI: 10.1016/j.ijheatmasstransfer.2024.126384

Laryssa Sueza Raffa , Matt Ryall , Nick S. Bennett , Lee Clemon

High computational power and miniaturisation of modern electronics lead to high heat generation, compounded by the decreased available area for heat dissipation. This challenge is exacerbated in space environments due to the lack of convection. Phase change materials (PCM) are a strong option for the passive thermal management of satellites. However, their behaviour in vacuum is unclear. This study experimentally investigates and compares the performance of non-PCM and PCM-based thermal control modules under atmospheric pressure and vacuum conditions. A stainless steel heat sink with internal planar fins was tested using a printed circuit board (PCB) to produce three input power levels, simulating the heat dissipated by satellite electronics. Paraffin wax was used as the PCM. The thermal performance is reported and analysed for both pressure conditions. A reduced-order numerical model was established to predict performance with low required computational effort. This work finds that electronics operating in vacuum displayed temperatures as much as 32.8% higher compared to those in atmosphere due to decreased heat dissipation resulting from the lack of convective heat transfer. In addition, PCM had a greater impact in reducing the electronics temperature in vacuum than at atmospheric pressure. The presence of 6 g of PCM lowered the electronics temperatures by up to 18.0 °C in vacuum, and by up to 12.3 °C in atmospheric pressure. That amount of PCM doubled the electronics operating time under both pressure conditions at high power. The findings of this work contribute to understanding the performance variances of non-PCM and PCM-based heat sinks under different pressure conditions to further improve the design of thermal management modules for satellites.

现代电子设备的高计算能力和微型化导致了高发热量，而可用的散热面积减少又加剧了这一问题。由于缺乏对流，这一挑战在太空环境中更加严峻。相变材料（PCM）是卫星被动热管理的一个有力选择。然而，它们在真空中的表现尚不明确。本研究通过实验研究并比较了非 PCM 和 PCM 热控制模块在大气压和真空条件下的性能。使用印刷电路板（PCB）对带有内部平面散热片的不锈钢散热器进行了测试，以产生三个输入功率级别，模拟卫星电子设备的散热情况。石蜡被用作 PCM。报告和分析了两种压力条件下的热性能。建立了一个低阶数值模型，以较低的所需计算量预测性能。这项研究发现，在真空中工作的电子元件的温度比在大气中工作的电子元件的温度高出 32.8%，这是由于缺乏对流传热导致散热减少。此外，与大气压相比，PCM 对降低真空中电子元件温度的影响更大。6 克 PCM 可使真空中的电子元件温度降低 18.0 °C，使大气压下的电子元件温度降低 12.3 °C。在这两种压力条件下，PCM 的用量使电子元件在高功率下的工作时间延长了一倍。这项研究成果有助于了解非 PCM 和 PCM 散热器在不同压力条件下的性能差异，从而进一步改进卫星热管理模块的设计。

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引用次数: 0

Multi-objective optimization of active cooling and compressive load-bearing performance of truss-cored sandwich panel using genetic algorithm 利用遗传算法对三层夹芯板的主动冷却和抗压承重性能进行多目标优化

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-08 DOI: 10.1016/j.ijheatmasstransfer.2024.126404

Shibin Peng , Yinglong Sheng , Jiaxin Ren , Feng Jin , Shangsheng Feng

Sandwich panels with truss cores offer versatile capabilities, such as heat dissipation and load-bearing, making them promising options for multifunctional applications. However, optimizing thermal and mechanical performance often requires different structural parameters for the sandwich cores. Therefore, it is necessary to balance thermal and mechanical performance during structural design. In this study, a pyramid lattice-cored sandwich panel was evaluated under simultaneous thermal and pressure loads. The multifunctional design of the sandwich panel was optimized using the NSGA-II algorithm to enhance active cooling efficiency, load-bearing capacity, and lightweight index. The design variables included core parameters such as strut diameter, inclination angle, and core height. The active cooling performance of the sandwich panel was assessed using CFD simulation with the k-ω SST turbulence model. Meanwhile, the compressive load-bearing capacity and lightweight index were evaluated using theoretical relations. To validate the optimization results, forced convection experiments and quasi-static out-of-plane compression tests were conducted. From the Pareto solutions predicted by the NSGA-II algorithm, the optimal design point was identified. The predicted heat transfer coefficient and collapse strength of the optimal design were within 15 % and 6.3 %., respectively, of the experimental data. Compared to the initial design, the optimal design increased the heat transfer coefficient by 79.1 % and the collapse strength by 40.6 %, while maintaining nearly the same relative density.

带有桁架芯材的夹芯板具有散热和承重等多种功能，是多功能应用的理想选择。然而，要优化热性能和机械性能，往往需要对夹芯采用不同的结构参数。因此，有必要在结构设计时平衡热性能和机械性能。本研究对一种金字塔格状夹芯板进行了热负荷和压力负荷同时作用下的评估。采用 NSGA-II 算法对夹芯板的多功能设计进行了优化，以提高主动冷却效率、承载能力和轻质指数。设计变量包括芯材参数，如支柱直径、倾斜角度和芯材高度。利用 k-ω SST 湍流模型进行 CFD 模拟，评估了夹芯板的主动冷却性能。同时，利用理论关系评估了抗压承载能力和轻质指数。为了验证优化结果，还进行了强制对流实验和准静态平面外压缩试验。根据 NSGA-II 算法预测的帕累托方案，确定了最佳设计点。优化设计所预测的传热系数和坍塌强度分别在实验数据的 15% 和 6.3% 以内。与初始设计相比，最优设计将传热系数提高了 79.1%，塌陷强度提高了 40.6%，同时保持了几乎相同的相对密度。

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引用次数: 0

Heat transfer enhancement for electro-thermo-convection of FENE-P viscoelastic fluid in a square cavity 方形空腔中 FENE-P 粘弹性流体电热对流的传热增强效应

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-08 DOI: 10.1016/j.ijheatmasstransfer.2024.126390

Bo Guo , Rong Liu , Xinhui Si

This study numerically investigates the heat transfer enhancement for viscoelastic electro-thermo-convection in a two-dimensional differentially heated cavity with injection from below. The flow motion is assumed to be incompressible, which is driven by the Coulomb force and the thermal buoyant force. The polymers are described by the FENE-P model which exhibits typical shear-thinning and elastic properties. Based on the extensibility parameter (

L

), the cases are divided into several scenarios, corresponding to weak elasticity with strong shear-thinning, moderate elasticity with moderate shear-thinning, and strong elasticity with weak shear-thinning, respectively. We find that the competition between the shear-thinning and elasticity dominates the flow state and heat transport. The shear-thinning effect tends to facilitate heat transfer, while its elastic properties tend to decrease it. In the scenario of weak elasticity with strong shear-thinning (

L^{2} = 10

), the polymer additives significantly improve the heat transfer enhancement (HTE) of the electric field as the polymer viscosity ratio (

β

) decreases or Weissenberg number (

W i

) increases, where the maximum HTE reaches around 92.1%. The amount of HTE first increases rapidly with

W i

but then remains almost constant once a critical

W i

is exceeded. However, the HTE significantly decreases in the scenario of strong elasticity with weak shear-thinning (

300 \leq L \leq 1000

) since the elasticity dominates over the shear-thinning. These heat transfer performances are then corroborated with the boundary layer and kinetic energy budget analysis.

本研究以数值方法研究了粘弹性电热对流在自下而上注入的二维差热空腔中的传热增强问题。假设流动运动不可压缩，由库仑力和热浮力驱动。聚合物由 FENE-P 模型描述，该模型具有典型的剪切稀化和弹性特性。根据延伸性参数 (L)，情况被分为几种，分别对应于弱弹性与强剪切稀化、中等弹性与中等剪切稀化以及强弹性与弱剪切稀化。我们发现，剪切稀化和弹性之间的竞争主导了流动状态和热量传输。剪切稀化效应倾向于促进热传递，而其弹性特性则倾向于降低热传递。在弹性弱、剪切稀化强（L2=10）的情况下，随着聚合物粘度比（β）的降低或魏森伯格数（Wi）的增加，聚合物添加剂可显著改善电场的传热增强（HTE），其中最大 HTE 约为 92.1%。HTE 量先是随着 Wi 的增加而迅速增加，但一旦超过临界 Wi，HTE 量就几乎保持不变。然而，在强弹性和弱剪切稀化（300≤L≤1000）的情况下，由于弹性比剪切稀化占优势，因此 HTE 明显降低。边界层和动能预算分析证实了这些传热性能。

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引用次数: 0

The Coupling Effect of Surface Vibration and Micro-structure on Spray Cooling Heat Transfer 表面振动和微观结构对喷雾冷却传热的耦合效应

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-08 DOI: 10.1016/j.ijheatmasstransfer.2024.126409

Xinwen Chen , Aimin Du , Meng Zhang , Zhaohua Li , Kun Liang , Yuqi Qian

Although existing studies have emphasized the effects of micro-structured surfaces and vibration conditions on spray cooling efficiency. However, there is a research gap on how the coupling effect of these two factors affects spray cooling heat transfer. Therefore, in this study, the heat dissipation capacity of spray cooling under different vibration and microstructure size conditions is investigated experimentally using commercial HFE-649 as the coolant. The coolant is an electronic fluid with a global warming potential of only 1. Its low boiling point (49°C), which facilitates the early realisation of the phase change process, has a high potential for application in thermal management systems. The study reveals that both vibration and micro-structured surfaces significantly enhance the heat flux and heat transfer coefficient (HTC) in spray cooling. The combined effect of vibration and microstructures results in a more pronounced enhancement of cooling capacity, with the HTC increasing by 44% compared to a static smooth surface. As the vibration frequency and the side length (

w

) of the square fins on the micro-structured surface increase, the heat flux, HTC, critical heat flux (CHF), cooling efficiency, and heat transfer enhancement ratio (HTER) all show an increasing trend. However, at high vibration Reynolds numbers (

R e_{v}

) (15708) and the

w

of the square fins of 0.8mm and 1.0mm, there is a notable decline in spray cooling capacity due to the excessively high

R e_{v}

enhances the reciprocating motion of the liquid film, causing the film to inadequately spread and continuously accumulate around the edges. A correlation for heat dissipation capability of spray cooling under the coupled effects of vibration and micro-structured surfaces was derived and fitted, with the error in CHF within 12%.

尽管现有研究强调了微结构表面和振动条件对喷雾冷却效率的影响。然而，关于这两个因素的耦合效应如何影响喷雾冷却传热的研究还存在空白。因此，本研究使用商用 HFE-649 作为冷却剂，通过实验研究了不同振动和微结构尺寸条件下喷雾冷却的散热能力。该冷却剂是一种全球变暖潜能值仅为 1 的电子液体，其沸点较低（49°C），有利于尽早实现相变过程，在热管理系统中具有很大的应用潜力。研究表明，振动和微结构表面都能显著提高喷雾冷却中的热通量和传热系数（HTC）。在振动和微结构的共同作用下，冷却能力得到了更明显的提高，与静态光滑表面相比，热传导系数提高了 44%。随着振动频率和微结构表面上方形翅片边长（w）的增加，热通量、HTC、临界热通量（CHF）、冷却效率和传热增强比（HTER）都呈上升趋势。然而，在高振动雷诺数（Rev）（15708）和 0.8 毫米和 1.0 毫米的方形翅片宽度条件下，由于过高的 Rev 会增强液膜的往复运动，导致液膜无法充分扩散并在边缘不断积聚，因此喷雾冷却能力明显下降。推导并拟合了振动和微结构表面耦合效应下喷雾冷却散热能力的相关性，CHF 误差在 12% 以内。

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引用次数: 0

Investigation of bubble interaction in a temporal and spatial heat flux partitioning model for subcooled flow boiling 过冷流沸腾时空热通量分配模型中的气泡相互作用研究

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-08 DOI: 10.1016/j.ijheatmasstransfer.2024.126389

Shihao Yang , Bo Ren , Lixin Yang , Chong Chen , Qi Lu , Zonglan Wei , Jian Deng

CFD methodology for subcooled flow boiling is significantly affected by the heat flux partitioning model, which plays a crucial role in predicting the mass source term generated by wall boiling of the liquid phase. Although numerous models have been proposed, most research efforts have focused on the spatial dimensions of boiling heat transfer mechanisms, neglecting the temporal aspect. This study presents a heat flux partitioning model for subcooled flow boiling that considers both temporal and spatial dimensions. The model accounts for the contribution of heat flux from the superheated liquid layer during the bubble growth stage, liquid convection during the bubble wait stage within the bubble influence area in the temporal dimension, and heat flux from the overlapping area of bubble influence in the spatial dimension. An approach was developed to determine the bubble influence area by considering the bubble interaction based on the stochastic nature of nucleation sites on the heated wall, verified by the Monte Carlo method. The bubble dynamics parameters were experimentally derived to reduce the uncertainty associated with the boiling sub-models on the calculation. A comparative analysis of boiling curves and wall heat flux partitioning was conducted between the present model and the RPI model under various flow conditions. The results indicate that both models could reasonably predict the boiling curve. However, the RPI model tends to over-predict the proportion of evaporative heat flux, which is considered a weakness. Based on physical principles, the present model accurately captures the fundamental trend of wall heat flux partitioning. This research enhances the understanding of subcooled flow boiling and increases confidence in multiphase CFD methodology predictions.

过冷流沸腾的 CFD 方法受热流分区模型的影响很大，该模型在预测液相壁面沸腾产生的质量源项方面起着至关重要的作用。虽然已经提出了许多模型，但大多数研究工作都侧重于沸腾传热机制的空间维度，而忽略了时间方面。本研究提出了一种同时考虑时间和空间维度的过冷流动沸腾热通量分配模型。该模型在时间维度上考虑了气泡生长阶段过热液层的热通量贡献，气泡等待阶段气泡影响区域内的液体对流，以及空间维度上气泡影响重叠区域的热通量。根据加热壁上成核点的随机性，开发了一种考虑气泡相互作用的方法来确定气泡影响区域，并通过蒙特卡罗方法进行了验证。气泡动力学参数通过实验得出，以减少沸腾子模型在计算中的不确定性。对本模型和 RPI 模型在各种流动条件下的沸腾曲线和壁面热通量分配进行了比较分析。结果表明，两种模型都能合理预测沸腾曲线。然而，RPI 模型倾向于过度预测蒸发热通量的比例，这被认为是一个弱点。本模型基于物理原理，准确捕捉了壁面热通量分配的基本趋势。这项研究加深了人们对过冷流动沸腾的理解，增强了对多相 CFD 方法预测的信心。

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引用次数: 0

Strain-driven anisotropic enhancement in the thermal conductivity of KCaBi: the role of optical phonons 应变驱动的 KCaBi 热导率各向异性增强：光学声子的作用

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-08 DOI: 10.1016/j.ijheatmasstransfer.2024.126364

Xue-Kun Chen , Yue Zhang , Qing-Qing Luo , Pin-Zhen Jia , Wu-Xing Zhou

Acoustic phonons have long been believed to dominate the lattice thermal conductivity (

κ_{l}

) and the contribution of optical phonons can be neglected in crystal structures. KCaBi, as a high-throughput screening semiconductor with ultralow

κ_{l}

[J. Am. Chem. Soc. 144, 4448 (2022)], has been demonstrated that the contribution of optical phonons plays an important role in thermal transport. In this work, by solving the Boltzmann transport equation, it is found that the

κ_{l}

of KCaBi is 2.2 at 300K, with acoustic phonons dominating the z-direction

κ_{l}

and optical phonons contributing around 50% to the x-direction

κ_{l}

under the four-phonon picture. The uncommon contribution of optical phonons also manifests the possibility of tuning the

κ_{l}

anisotropy based on optical phonons. Following this line of thinking, it is found that applying tensile strain can cause a more pronounced decrease of acoustic phonon contribution than that of optical counterpart due to the highly dispersive optical branches, thus enhancing the anisotropic ratio of

κ_{l}

. Moreover, the microscopic mechanism is elucidated by analyzing the phonon dispersion relation, phonon mode-wise contribution and phonon scattering rates. Our study could provide appealing alternatives for the regulation of phonon transport from the viewpoint of optical phonons.

长期以来，人们一直认为声子在晶格热导率（κl）中占主导地位，在晶体结构中可以忽略光学声子的贡献。KCaBi 作为一种具有超低 κl 的高通量筛选半导体[J. Am. Chem. Soc. 144, 4448 (2022)]，已被证明光学声子的贡献在热传输中起着重要作用。在这项研究中，通过求解波尔兹曼输运方程，发现 KCaBi 在 300K 时的κl 为 2.2，在四声子图景下，声子在 z 方向的κl 中占主导地位，而光学声子对 x 方向的κl 的贡献约为 50%。光声子的贡献并不常见，这也体现了根据光声子调整 κl 各向异性的可能性。按照这一思路，研究发现，由于光学分支的高度色散性，施加拉伸应变会导致声子贡献比光学声子贡献更明显地减少，从而提高κl 的各向异性比。此外，通过分析声子色散关系、声子模式贡献和声子散射率，我们还阐明了微观机制。我们的研究可以从光学声子的角度为声子传输的调节提供有吸引力的替代方案。

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引用次数: 0