International Journal of Heat and Mass Transfer最新文献_第6页

Theoretical analysis of effective thermal conductivity for clayey hydrate-bearing sediments during hydrate dissociation and reformation processes 粘土质含水沉积物在水合物解离和重整过程中的有效导热性理论分析

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-04 DOI: 10.1016/j.ijheatmasstransfer.2024.126386

Jiadi Tang , Gang Lei , Yihan Shang

In general, apart from hydrate dissociation, the hydrate reformation phenomenon may occur during the natural gas hydrate (NGH) exploitations, which increases the risk of blockage accidents and should be further understood and controlled. Since the effective thermal conductivity (ETC) of the hydrate-bearing sediment (HBS) is a critical parameter controlling the heat transfer process and significantly affecting hydrate dissociation and reformation processes, it should be precisely predicted for enhancing the safe, efficient, and stable NGH exploitations. Thus, in this work, a novel analytical ETC model of HBS is proposed not only to quantitatively characterize various mechanisms during hydrate dissociation and reformation processes, but also to accurately determine ETC under effective stress conditions. The ETC predictions of the proposed model are validated against available experimental ETC data under various conditions, enhancing the reasonability of this model. And effects of several crucial parameters on ETC are deeply investigated. Results show that, with the increasing effective stress (axial stress and radial stress), ETC of HBS increases. And ETC increases in the early stage of hydrate dissociation, however, as the hydrate dissociation continues, the ETC of HBS decreases. Additionally, during hydrate reformation process, ETC of HBS shows a negative relation with the hydrate saturation under excess water condition and shows a positive relation under excess gas condition. Notably, the proposed model can offer insights into heat transfer characteristics under various NGH exploitation conditions, helping optimize the extraction plans.

一般来说，在天然气水合物（NGH）开采过程中，除了水合物解离外，还可能出现水合物重整现象，这增加了堵塞事故的风险，应进一步了解和控制。由于含水合物沉积物（HBS）的有效热导率（ETC）是控制传热过程的关键参数，对水合物解离和重整过程有重要影响，因此应精确预测其有效热导率，以提高天然气水合物开采的安全性、高效性和稳定性。因此，本研究提出了一种新的 HBS ETC 分析模型，不仅可以定量分析水合物解离和重整过程中的各种机理，还可以准确确定有效应力条件下的 ETC。所提模型的 ETC 预测值与各种条件下的现有实验 ETC 数据进行了验证，增强了该模型的合理性。此外，还深入研究了几个关键参数对 ETC 的影响。结果表明，随着有效应力（轴向应力和径向应力）的增加，HBS 的 ETC 也随之增加。在水合物解离的早期阶段，ETC 会增加，但随着水合物解离的继续，HBS 的 ETC 会减小。此外，在水合物重整过程中，HBS 的 ETC 与过量水条件下的水合物饱和度呈负相关，而与过量气体条件下的水合物饱和度呈正相关。值得注意的是，所提出的模型可以帮助人们深入了解各种 NGH 开采条件下的传热特性，有助于优化开采计划。

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引用次数: 0

Experimental investigation of the heat transfer characteristics of CO2 at supercritical pressures flowing in heated vertical pipes 超临界压力下二氧化碳在加热垂直管道中流动的传热特性实验研究

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-04 DOI: 10.1016/j.ijheatmasstransfer.2024.126367

Konstantinos Theologou, Rainer Mertz, Jörg Starflinger

Supercritical CO₂ shows great potential as a working fluid in power plant cycles due to its moderate critical pressure of 7.38 MPa and critical temperature of 30.98 °C, closely matching typical heat sink temperatures. Understanding the heat transfer characteristics of sCO₂ is crucial for designing cycle components. This publication presents a systematic analysis of sCO₂ heat transfer in two heated vertical pipes with 4 and 8 mm inner diameters, with both upward and downward flow at pressures of approximately 7.75, 8.00, and 9.50 MPa, and flow inlet temperatures between 5 and 40 °C, based on 196 experiments. The study investigates a range of mass fluxes from 400 to 2000 kg/m²s and heat fluxes from 10 to 195 kW/m², resulting in a heat to mass flux ratio of 6 to 275 J/kg. The findings reveal enhanced, normal, and deteriorated heat transfer within the experimental dataset. Buoyancy effects are identified as the main cause of deteriorated heat transfer in the investigated parameter range, with flow acceleration showing no significant influence on heat transfer. A new proposed dimensional criterion categorises 36 out of 119 experiments with upward flow in the deteriorated heat transfer regime, accompanied by temperature peaks rising to 47 K. Thermal inflow lengths range from 0 to 480 inner pipe diameters, with some experiments not achieving a thermally fully developed flow over the entire pipe length. Based on a comparison with approximately 8950 experimental data points, two Nusselt correlations are found, capable of reproducing the experimental results with a mean absolute deviation of around 30 %. This publication provides valuable data for validating numerical models and developing correlations to predict the heat transfer of supercritical fluids.

超临界二氧化碳的临界压力为 7.38 兆帕，临界温度为 30.98 °C，与典型的散热器温度非常接近，因此在发电厂循环中用作工作流体具有巨大潜力。了解 sCO2 的传热特性对于设计循环组件至关重要。本出版物基于 196 次实验，对两个内径分别为 4 毫米和 8 毫米的加热垂直管道中的 sCO2 传热进行了系统分析，这两个管道在压力约为 7.75、8.00 和 9.50 兆帕、流量入口温度介于 5 和 40 °C之间的条件下，均向上和向下流动。研究调查了 400 至 2000 kg/m2s 的质量流量范围和 10 至 195 kW/m2 的热流量范围，得出热量与质量流量比为 6 至 275 J/kg。研究结果表明，在实验数据集中，热传递有增强、正常和恶化三种情况。在所研究的参数范围内，浮力效应是导致传热恶化的主要原因，而流动加速度对传热没有显著影响。新提出的尺寸标准将 119 次实验中的 36 次实验归类为传热机制恶化的向上流动实验，伴随着温度峰值上升到 47 K。在与大约 8950 个实验数据点进行比较的基础上，发现了两种努塞尔特相关性，能够再现实验结果，平均绝对偏差约为 30%。该出版物为验证数值模型和开发相关数据以预测超临界流体的传热提供了宝贵的数据。

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引用次数: 0

Particle transport and turbulence modification in unstably stratified mixed convection within a horizontal channel 水平通道内非稳定分层混合对流中的粒子输送和湍流修正

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-04 DOI: 10.1016/j.ijheatmasstransfer.2024.126377

Ming Pan , Lian Shen , Quan Zhou , Yuhong Dong

Particle transport and turbulence modification in an unstably stratified, particle-laden turbulent flow within a horizontal channel is studied via direct numerical simulations combined with Lagrangian point‒particle tracking techniques. Two-way coupling in momentum and energy is considered in dilute gas‒solid flows under mixed convection (synergistic effects of shear and buoyancy). For comparison, simulations of neutral turbulence are also conducted with equivalent parameters. The study reveals that large-scale longitudinal vortical structures induce significant spatial heterogeneity in the spanwise distribution of inertial particles. This heterogeneity is characterized by an increase in the particle concentration on the side of the cold plume and a corresponding decrease on the side of the hot plume. In the context of unstably stratified turbulence, particles reduce the fluid streamwise velocity and promote its profile toward symmetry. This phenomenon contrasts with that observed in neutral flows, where particles induce velocity asymmetry by dragging the upper flow and accelerating the lower flow. A quantitative analysis of the heat flux indicates that particles absorb heat as they settle, thereby reducing the average temperature of the flow. Buoyancy effects slow the settling and reinjection of particles, which in turn diminishes thermal energy absorption. Particles with higher inertia preferentially settle on the cooler plume side, minimizing their participation in heat exchange due to prolonged durations of repeated wall collisions.

通过直接数值模拟结合拉格朗日点粒子跟踪技术，研究了水平通道内不稳定分层、富含粒子的湍流中的粒子传输和湍流修正。在混合对流（剪切力和浮力的协同效应）下的稀释气固流中，考虑了动量和能量的双向耦合。为了进行比较，还使用等效参数对中性湍流进行了模拟。研究表明，大尺度纵向涡旋结构会导致惯性粒子的跨度分布出现显著的空间异质性。这种异质性的特点是冷羽流一侧的粒子浓度增加，而热羽流一侧的粒子浓度相应减少。在不稳定分层湍流的情况下，颗粒会降低流体的流向速度，并使其轮廓趋于对称。这种现象与在中性流中观察到的现象截然不同，在中性流中，粒子通过拖曳上层流体和加速下层流体，导致速度不对称。对热通量的定量分析表明，颗粒在沉降时会吸收热量，从而降低气流的平均温度。浮力效应减缓了颗粒的沉降和再喷射，进而减少了热能吸收。惯性较大的颗粒优先沉降在温度较低的羽流一侧，由于壁面反复碰撞的持续时间较长，它们参与热交换的程度降到了最低。

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引用次数: 0

Adaptive fractional physics-informed neural networks for solving forward and inverse problems of anomalous heat conduction in functionally graded materials 用于解决功能分级材料异常热传导正演和反演问题的自适应分数物理信息神经网络

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-03 DOI: 10.1016/j.ijheatmasstransfer.2024.126393

Xingdan Ma , Lin Qiu , Benrong Zhang , Guozheng Wu , Fajie Wang

In this paper, adaptive fractional physics-informed neural networks (PINNs) are employed to solve the forward and inverse problems of anomalous heat conduction in three-dimensional functionally graded materials. In adaptive fractional PINNs, the finite difference L1 scheme is employed to discretize the time fractional derivatives in anomalous heat conduction problems. By combining the finite difference L1 scheme with automatic differentiation technique, adaptive fractional PINNs minimize a loss function constructed based on the governing equation, initial and boundary conditions to obtain solutions to heat conduction problems. To avoid competition among various loss terms during the training process, an adaptive loss balancing algorithm is adopted to balance the interactions among different terms of the loss functions. In addition, polynomial basis functions are used to expand unknown functions characterizing material parameters or heat sources, aiming to enhance the performance of adaptive fractional PINNs in resolving inverse problems. Five numerical examples involving forward, inverse, and nonlinear problems related to anomalous heat conduction are carried out to demonstrate the feasibility and effectiveness of adaptive fractional PINNs.

本文采用自适应分数物理信息神经网络（PINNs）来解决三维功能分级材料中的反常热传导正演和反演问题。在自适应分数 PINNs 中，采用有限差分 L1 方案来离散异常热传导问题中的时间分数导数。通过将有限差分 L1 方案与自动微分技术相结合，自适应分数 PINN 最大限度地减小了根据控制方程、初始条件和边界条件构建的损失函数，从而获得热传导问题的解决方案。为避免训练过程中各种损失项之间的竞争，采用了自适应损失平衡算法来平衡损失函数不同项之间的相互作用。此外，还使用多项式基函数来扩展表征材料参数或热源的未知函数，旨在提高自适应分数 PINN 在解决逆问题时的性能。本文通过五个涉及反常热传导的正向、反向和非线性问题的数值示例，证明了自适应分数 PINN 的可行性和有效性。

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引用次数: 0

Kinetic Monte Carlo modeling of heterogeneous catalysis on silica thermal protective materials based on reactive molecular dynamics simulation 基于反应分子动力学模拟的二氧化硅热保护材料异相催化动力学蒙特卡罗模型

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-02 DOI: 10.1016/j.ijheatmasstransfer.2024.126378

Qin Li , Xiaofeng Yang , Wei Dong , Yanxia Du

Heterogeneous catalytic recombination of chemically dissociated atoms occurring on thermal protective materials significantly increases the thermal load borne by high-speed aircraft, but the intricate nature of microscopic reaction dynamics poses a formidable challenge in its analysis within the context of macroscopic heat and mass transfer calculations. Reactive molecular dynamics (RMD) method is helpful in simulating the complicated chemical mechanisms of the gas-surface interaction, while the high computational cost limits its application to larger spatial and temporal scales. To quickly obtain the time evolution of surface catalysis of dissociated atoms on thermal protective materials and provide reactive boundary conditions for numerical simulation of the high-speed flow field, a kinetic Monte Carlo (KMC) algorithm specified for this phenomenon was developed. Rate parameters of the elementary reaction steps were extracted from ReaxFF-based molecular dynamics simulation using proper post-processing method. Elementary reaction steps and active site configuration were integrated into the RMD-based KMC algorithm to cater to the characteristics of catalysis on silica thermal protective materials. The RMD-based KMC modeling method was proved to be accurate and efficient in predicting the recombination coefficients and surface configuration, with an error of less than 15 %. Compared to RMD simulations, the KMC modeling significantly reduces the computational cost of surface reaction dynamics by approximately 2 × 10⁵ times. RMD-based KMC method can contribute to the cross-scale coupling between molecular-level research and continuum computation.

热防护材料上发生的化学解离原子的异相催化重组大大增加了高速飞机所承受的热负荷，但微观反应动力学的复杂性给在宏观传热和传质计算的背景下对其进行分析带来了巨大挑战。反应分子动力学（RMD）方法有助于模拟气体与表面相互作用的复杂化学机制，但高昂的计算成本限制了其在较大时空尺度上的应用。为了快速获得热防护材料表面离解原子催化的时间演化，并为高速流场的数值模拟提供反应边界条件，我们开发了一种针对这一现象的动力学蒙特卡洛（KMC）算法。利用适当的后处理方法，从基于 ReaxFF 的分子动力学模拟中提取了基本反应步骤的速率参数。基本反应步骤和活性位点构型被整合到基于 RMD 的 KMC 算法中，以适应硅热保护材料催化反应的特点。事实证明，基于 RMD 的 KMC 建模方法在预测重组系数和表面构型方面准确高效，误差小于 15%。与 RMD 模拟相比，KMC 建模大大降低了表面反应动力学的计算成本，降低了约 2 × 105 倍。基于 RMD 的 KMC 方法有助于分子水平研究与连续计算之间的跨尺度耦合。

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引用次数: 0

Flow and heat transfer characteristics of supercritical CO2 in serpentine tubes under semi-circumferential heating conditions 半环流加热条件下蛇形管中超临界二氧化碳的流动和传热特性

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-02 DOI: 10.1016/j.ijheatmasstransfer.2024.126304

Kun Wang , Xiang Zhang , Zhan-Peng Zhang , Zhen-Dong Zhang , Yuan-Hong Fan , Chun-Hua Min , Zhong-Hao Rao

The tubular solar receiver is one of the most promising candidates for direct supercritical carbon dioxide (S-CO₂) solar receivers, which can improve the pressure-bearing performance by increasing the wall thickness of the tube. However, increasing wall thickness induces larger conductive thermal resistance, leading to higher wall temperature and lower thermal efficiency of the receiver. The serpentine tube can enhance the convective heat transfer, mitigating the negative impacts of the increased wall thickness. Nonetheless, the flow and heat transfer characteristics of S-CO₂ in serpentine tubes under semi-circumferential heating conditions require further investigation. In this work, the flow and heat transfer characteristics of S-CO₂ in a serpentine tube under semi-circumferential heating conditions were numerically investigated. The results showed that in high Reynolds number flows, the radial resultant buoyancy force, dominated by centrifugal buoyancy, induces secondary flow in the tube, improving the field synergy of the cross-section inside the tube. Under the influence of secondary flow, the high-temperature S-CO₂ accumulates on the heated side of the concave area and on the insulated side of the convex area, causing local heat transfer deterioration in such areas, but the secondary flow enhances the overall heat transfer performance of the serpentine tube. Compared to circumferential heating, the heat transfer coefficient with semi-circumferential heating is enhanced in the concave areas while deteriorated in the convex areas.

管式太阳能接收器是最有前途的直接超临界二氧化碳（S-CO2）太阳能接收器之一，它可以通过增加管壁厚度来提高承压性能。然而，增加管壁厚度会产生较大的传导热阻，导致管壁温度升高，降低接收器的热效率。蛇形管可以增强对流传热，减轻壁厚增加带来的负面影响。然而，蛇形管中 S-CO2 在半环流加热条件下的流动和传热特性还需要进一步研究。在这项工作中，对半圆形加热条件下 S-CO2 在蛇形管中的流动和传热特性进行了数值研究。结果表明，在高雷诺数流动中，以离心浮力为主的径向结果浮力在管内引起二次流动，改善了管内横截面的场协同作用。在二次流动的影响下，高温 S-CO2 聚集在凹面区域的加热侧和凸面区域的隔热侧，导致这些区域的局部传热恶化，但二次流动提高了蛇形管的整体传热性能。与圆周加热相比，半圆周加热的传热系数在凹面区域有所提高，而在凸面区域则有所降低。

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引用次数: 0

Numerical and experimental investigations on the effect of skeleton shapes and heat transfer directions on water freezing in porous media 骨架形状和传热方向对多孔介质中水冻结影响的数值和实验研究

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-02 DOI: 10.1016/j.ijheatmasstransfer.2024.126392

Qingyu Yang , Tao Yang , Yingying Yang , Jun Shen

Incorporating porous skeletons into PCMs is an effective strategy for enhancing their thermal properties. However, this approach increases the complexity of the heat transfer process and poses a challenge to accurate modeling. This study investigates the water freezing process in porous skeletons with various shapes and heat transfer directions through experiments and numerical simulations. The model employs the hybrid finite element method with mesh adaptation to optimize numerical solutions. The experimental and simulation results are in good agreement, which validates the accuracy of this model. The study aims to reveal the evolution mechanisms of the phase interface, temperature field, and freezing rate of water in various porous skeletons, enhancing the theoretical foundation and offering insights for practical applications. Results show that the square steel skeleton exhibits the highest freezing rate among the tested skeleton shapes, while the rhombus resin skeleton demonstrates the slowest. Furthermore, the square skeleton shows the smallest interface deflection before and after the pores, while the rhombus skeleton presents the largest. Additionally, vertical heat transfer from bottom to top increases the freezing rate by 38.97% compared to horizontal heat transfer from left to right.

在 PCM 中加入多孔骨架是增强其热学特性的有效策略。然而，这种方法增加了传热过程的复杂性，给精确建模带来了挑战。本研究通过实验和数值模拟研究了水在不同形状和传热方向的多孔骨架中的冻结过程。模型采用了网格自适应的混合有限元法来优化数值解。实验和模拟结果吻合良好，验证了该模型的准确性。该研究旨在揭示各种多孔骨架中水的相界面、温度场和冻结率的演变机理，增强理论基础，并为实际应用提供启示。结果表明，在所测试的骨架形状中，方形钢骨架的冻结速率最高，而菱形树脂骨架的冻结速率最慢。此外，方形骨架在孔隙前后的界面挠度最小，而菱形骨架的界面挠度最大。此外，与从左到右的水平热传递相比，从下到上的垂直热传递使冻结率提高了 38.97%。

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引用次数: 0

Enhancing nanoscale phase-change heat transfer by collaborative roles of surface functionalization and external electric field 通过表面功能化和外加电场的协同作用加强纳米级相变传热

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-01 DOI: 10.1016/j.ijheatmasstransfer.2024.126363

Wenxiang Liu , Yixin Xu , Zhigang Li , Fei Duan , Yanguang Zhou

Understanding the mechanism behind phase-change heat transfer and designing new strategies to improve the heat transfer coefficient is crucial for numerous applications, such as heat engines, cooling, and steam generators. Here, we demonstrate the heat transfer coefficient at the Au surface can be improved by 113 % utmost via applying an external electric field (EEF) and modifying the surface with functional groups (FGs). This enhancement is found to be resulting from the fast vapor-liquid transition and high thermal conductance across the solid-liquid interface. On the one hand, the EEF decreases water-vapor phase transition activation energy and therefore increases the evaporation rate. On the other hand, introducing the FGs at the Au surface increases the interfacial adhesion and bridges the interfacial inter-medium vibrational couplings, leading to an increasing thermal conductance of Au/water interfaces. The vibrational coupling between water and the FGs is further increased by the EEF which complements the decreased influence of EFF on the water-vapor phase transition activation energy at high temperatures. Our work here provides a collaborative strategy to enhance phase-change heat transfer on surfaces which could be beneficial to its related applications.

了解相变传热背后的机理并设计出提高传热系数的新策略对于热机、冷却和蒸汽发生器等众多应用至关重要。在这里，我们证明了通过施加外部电场（EEF）和用官能团（FGs）修饰金表面，可将金表面的传热系数最大提高 113%。这种提高源于固液界面的快速汽液转换和高热导率。一方面，EEF 降低了水汽相变活化能，从而提高了蒸发率。另一方面，在金表面引入 FGs 增加了界面粘附力，桥接了界面介质间的振动耦合，从而提高了金/水界面的热导率。EEF 进一步提高了水与 FGs 之间的振动耦合，补充了 EFF 对高温下水汽相变活化能影响的降低。我们的工作为增强表面的相变传热提供了一种合作策略，这将有利于其相关应用。

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引用次数: 0

Enhancing the energy storage/release performance of a triple-tube phase change storage unit with novel claw-shaped fins 利用新型爪形鳍片提高三管相变储能装置的能量存储/释放性能

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-01 DOI: 10.1016/j.ijheatmasstransfer.2024.126368

Hao Guo, Maocheng Tian

A novel claw-shaped fin has been developed to address the heat-transfer differences between the melting and solidification processes to enhance the efficiency of the melting/solidification cycles. The enthalpy-porous medium model simulated the phase change material's (PCM) melting and solidification process. The impact of branch number, length ratio (L), branch angle (α), and fin material on the PCM phase change process was analyzed utilizing liquid fraction/temperature contours, liquid fraction curves, and Nusselt numbers. Results indicate that the improvement in melting performance due to adding branches is primarily attributed to enhanced heat conduction and coordinates the radial solidification rate by improving the radial temperature response. For a fixed fin volume, increasing L and decreasing α are beneficial for reducing the PCM's melting and solidification times. Materials with lower thermal conductivity can weaken the ability of heat to transfer quickly from the fin base to the branches, thereby reducing the effectiveness of direct heat transfer to the PCM. Based on RSM, the L significantly impacts melting/solidification performance more than the α; the optimized four-branch fins (L = 1.7, α = 21.6°) reduce the melting/solidification time by 47.8 % compared to V-shaped fins. Further increasing branches does not significantly enhance heat-transfer performance.

为解决熔化和凝固过程中的传热差异，提高熔化/凝固循环的效率，开发了一种新型爪形鳍片。焓-多孔介质模型模拟了相变材料（PCM）的熔化和凝固过程。利用液体分数/温度等值线、液体分数曲线和努塞尔特数分析了支管数量、长度比 (L)、支管角度 (α)和鳍片材料对 PCM 相变过程的影响。结果表明，增加支管可改善熔化性能，这主要归因于增强了热传导，并通过改善径向温度响应来协调径向凝固速率。在翅片体积固定的情况下，增大 L 和减小 α 有利于缩短 PCM 的熔化和凝固时间。导热率较低的材料会削弱热量从鳍片基部快速传递到支部的能力，从而降低直接向 PCM 传热的效果。根据 RSM，L 比 α 对熔化/凝固性能的影响更大；与 V 形翅片相比，优化的四分支翅片（L = 1.7，α = 21.6°）可将熔化/凝固时间缩短 47.8%。进一步增加分支并不能明显提高传热性能。

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引用次数: 0

Flow boiling of saturated liquid nitrogen in a horizontal macro-tube under negative gauge pressure 水平宏管中饱和液氮在负表压下的流动沸腾

IF 5 2区工程技术 Q1 ENGINEERING, MECHANICAL

International Journal of Heat and Mass Transfer

Pub Date : 2024-11-01 DOI: 10.1016/j.ijheatmasstransfer.2024.126369

Yuan Gao , Yulong Li , Zuoxia Wang , Enze Ma , Heng Yu

This study explores the flow boiling of saturated liquid nitrogen within a 10 mm inner diameter horizontal macro-tube, focusing on the impact of negative gauge pressure. The experiments cover a range of inlet pressure from -79.9 to -50.2 kPa, mass flux from 29.7 to 108.8 kg/(m²·s), and heat flux from 0 to 28.64 kW/m². The investigation examines two-phase flow patterns, flow boiling instabilities, and heat transfer characteristics. Heat transfer coefficient (HTC) data are compared with predictions from four existing correlations, and a novel correlation is proposed. A uniform temperature distribution across the top and bottom walls suggests a prevalence of annular flow. Decreased pressure supports the formation of stable annular flow due to increased velocity difference between vapor and liquid phases resulting from the heightened liquid-vapor density ratio. Thermal oscillations are observed in the unstable annular flow near the inlet and in the intermittent dry-out region where the annular flow transitions to mist and vapor flow. Both pressure reduction and mass flux increase reduce thermal oscillations by minimizing gravitational effects and enhancing flow inertia. A decrease in pressure results in a reduced dry-out type critical heat flux (CHF) due to increased droplet entrainment flow rate. Convective evaporation is identified as the primary heat transfer mechanism, with nucleate boiling becoming apparent at high mass flux conditions. Decrease in pressure and the increase in mass flux both facilitate flow boiling heat transfer by suppressing thermal oscillations and enhancing evaporation at the liquid-vapor interface. Among the selected correlations, the Shah correlation demonstrates the highest prediction accuracy with a mean relative error (MRE) of 28.87 %. The newly proposed enhancement factor type model correlation shows even higher prediction accuracy with an MRE of 14.18 %.

本研究探讨了饱和液氮在内径为 10 毫米的水平宏管内的流动沸腾，重点是负表压的影响。实验的入口压力范围为 -79.9 至 -50.2 kPa，质量通量范围为 29.7 至 108.8 kg/（m2-s），热通量范围为 0 至 28.64 kW/m2。调查研究了两相流动模式、流动沸腾不稳定性和传热特性。将传热系数（HTC）数据与现有的四种相关性预测进行了比较，并提出了一种新的相关性。顶壁和底壁的温度分布均匀，表明环形流动普遍存在。由于液-汽密度比升高导致汽相和液相之间的速度差增大，压力降低支持形成稳定的环形流动。在入口附近的不稳定环形流以及环形流过渡到雾气和蒸汽流的间歇性干燥区，可以观察到热振荡。降低压力和增加质量通量都能最大限度地减少重力效应和提高流动惯性，从而减少热振荡。由于液滴夹带流速增加，压力降低会导致干燥型临界热通量（CHF）降低。对流蒸发被认为是主要的传热机制，在高质量通量条件下，核沸腾变得明显。压力的降低和质量通量的增加都能通过抑制热振荡和增强液汽界面的蒸发来促进流动沸腾传热。在选定的相关性中，Shah 相关性的预测精度最高，平均相对误差为 28.87%。新提出的增强因子类型模型相关性显示出更高的预测精度，平均相对误差为 14.18%。

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引用次数: 0