多孔表面新型复杂结构优化沸腾传热的实验研究

报道了R11在烧结多孔表面开槽时沸腾传热的实验研究，实验发现，与普通槽道和双空隙层多孔表面相比，沸腾换热增强，沸腾表现为液体灌注、槽道起泡、底部蒸干三个区，对特定的多孔层，开槽可获得更好的换热效果。带槽道的多孔表面实验件与均匀多孔表面相比，在相同壁面过热度（θ）条件下，热流密度（q）提高2－10倍，临界热流密度提高2－4倍。     

内表面烧结型多孔管的流动沸腾换热

采用流动沸腾传热试验平台,研究了2 m长铁基烧结型内表面多孔管竖直管内流动沸腾传热特性,利用流动沸腾传热学基本原理及公式计算了传热过程中的热通量、沸腾传热系数及相关参数,并考察了过热度和流速对多孔管流动沸腾传热性能的影响.结果表明:烧结型表面多孔管的流动沸腾传热能力优于同条件下的光滑管,内表面沸腾传热系数是同尺寸光滑管...     

多壁碳纳米管纳米流体的大容积沸腾

通过在直径为12 mm的沸腾表面进行的多壁碳纳米管阿拉伯树胶水溶液的大容积沸腾实验,研究其沸腾传热特性。纳米流体的沸腾传热效果弱于阿拉伯树胶水溶液,烧毁点的过热度增加而临界热流密度减小,同时,阿拉伯树胶水溶液的传热效果劣于水。纳米颗粒在沸腾加热表面富集、结垢引起液体密度、沸腾表面上活化核心数目的变化,随传热时间的延长,垢层结构包括毛细孔直径、空隙率、垢层厚度不断发生变化,进而引起蒸汽在毛细孔中的流动阻力不断增加、加热表面和垢层间热阻增加,沸腾表面的活化核心数目减小,阿拉伯树胶在蒸发表面的局部富集、黏度大大增加,最终导致沸腾传热恶化。     

平板滞止区内饱和液体喷流沸腾的临界热流密度

对高温平板滞止区内饱和液体的圆形喷流冲击沸腾的临界热流密度进行了系统的稳态实验研究。考察了不同液体、流速和喷流直径等系统条件对喷流沸腾临界热流密度的影响。建立了一个预示临界热流密度的半理论半经验型方程，其基本形式采用过去的研究结果，方程系数由本研究的实验数据拟合得到。研究结果证明，饱和液体喷流冲击沸腾的临界热流密度取决于液体物性、滞止冲击速度和喷流直径。本研究得到的半理论半经验公式在广泛的实验范围内能很好的预示喷流沸腾的临界热流密度。     

表面强化管外池沸腾传热特性研究

为实现节能降耗,开发了多种强化沸腾传热的高效换热管。以水为工质,在0.1MPa下对垂直光管、烧结多孔管和T槽管进行了池沸腾传热实验研究,并分析了沿管子轴向的温度分布。实验结果表明,烧结多孔管与T槽管能显著降低起始沸腾过热度、强化沸腾传热:烧结多孔管和T槽管的起始沸腾过热度比光管的低1.5K左右;烧结多孔管和T槽管的核态沸腾传热系数分别为光管的2.4～3.2倍和1.6～2.0倍。此外,烧结多孔管和T槽管能降低相同热流密度下的壁面温度,且有利于降低管子轴向的温差。     

泡沫陶瓷多孔介质内流体流动及表面传热模拟

气隙扩散蒸馏脱盐技术利用具有大比表面积的多孔介质作为蒸发器，海水在多孔介质内部流动并在表面蒸发，多孔介质起到了强化液体蒸发的作用;但由于多孔介质结构极其复杂，很难使用传统的实验技术从微观水平观测到多孔介质孔隙通道内流体的流动状态以及传热现象。针对此问题采用计算机数值模拟方法，拍摄实际碳化硅泡沫陶瓷CT图片，构建三维模型进行有限元模拟分析。结果表明，多孔介质内流体会优先通过较大孔隙通道。流体在多孔介质表面向环境空气的散热量随孔隙密度增大而增大，孔隙密度从10提高至30 PPI，散热量提高约1.43倍。进口热流体与环境空气温差越大，向环境的散热量越大，孔隙密度在30 PPI条件下，进口热流体温度从49.38增加至68.67 ℃，散热量提高近2.07倍。     

微纳结构铜表面低液位池沸腾实验研究

采用两步电镀法,在改变电流密度的情况下制备出具有不同微纳结构和润湿特性的A、B两个表面,并应用于低液位饱和池沸腾的实验研究中。通过与铜表面对比,发现两个表面在低热流密度情况下,传热系数要高于铜表面,但液位降低时传热系数提升幅度较小,原因在于铜表面沸腾气泡较大,液位降低气泡脱离有很大影响,而表面A、B沸腾气泡较小,液位降低主要对气泡扰动产生影响;当热流密度增大后,两个微纳结构表面气泡聚合严重,传热系数要低于铜表面,而且三个表面在高热流密度下,液位降低提升传热系数的幅度都有所降低。     

3×3棒束通道内低速流动沸腾传热特性的实验研究

以去离子水为实验介质,在入口温度为80~100℃、质量流速为0~100kg/(m2·s)、入口压力为0.1 MPa的参数范围内,对棒束通道内流动沸腾传热特性进行了实验研究,分析了质量流速和热流密度对流动沸腾传热系数的影响,考察不同子通道内的传热特性.根据实验工况选取了Liu-Winterton关系式、Kandlikar关系式、Gungor-Winterton关系式和Chen关系式对棒束通道内的流动沸腾传热系数进行预测,将实验结果与预测结果进行比较,并对4个关系式的预测结果进行统计评估.结果表明:Liu-Winterton关系式、Kandlikar关系式和Chen关系式的预测结果偏小,其中Chen关系式的预测结果误差最大,Gungor-Winterton关系式的预测结果更加准确.     

两相闭式热虹吸管传热特性研究

本文通过实验研究在不同热流密度下,两相闭式热虹吸管传热特性,并通过计算比较了三个较为常用的换热准则系统,同时提出了改进意见,为热管换热器的设计提供了较为可靠的依据。     

垂直矩形窄缝内的过冷流动沸腾换热性能

用高速摄像等方法研究了有压模化介质在单一垂直矩形窄缝流道内的气泡形态和传热情况 ,发现窄缝流动沸腾换热强化的原因在于流道尺寸较小 ,气泡的形状发生变化 ,增加了界面体积浓度 ,并强化了对加热面附近的扰动 ,使换热有所强化。通过与实际测量的壁温数据进行比较 ,发现用于计算大流道和池过冷沸腾换热的 Rohsenow关系式预测窄流道内高热流密度下的过冷流动沸腾换热的误差不大 ,但对于较低热流密度下的过冷流动沸腾时误差较大 ;通过最小二乘法对 Rohsenow关系式进行修正后 ,误差低于± 2 5 %。     

Experiment Analysis of Pool Boiling Heat Transfer in Bead Packed Porous Layers

The heat transfer of pool boiling in bead packed porous layers was experimentally investigated to analyze the effects of the bead material, bead diameter and the layer number of the porous bed on the transport of flux and the heat transfer coefficients. The glass and copper bead, the bead sizes of 4 mm and 6 mm as well as the bead packed porous structures ranging from one to three layers were chosen in the experiments. The pool boiling heat transfer in the bead packed porous structures and that on the plain surface were compared to analyze the enhancement of pool boiling heat transfer while the bead packed porous layers were employed. The maximum relative error between the collected experimental data of the pure water on a plain surface and the theoretical prediction of pool boiling using the Rohsenow correlation was less than 12%. Besides, the boiling bubble generation, integration and departure have a great effect on the pool boiling and were recorded with a camera in the bead stacked porous structures of the different layers and materials at different heat flux. All these results should be taken into account for the promotion and application of bead packed porous structures in pool boiling to enhance the heat transfer.     

Augmentation of boiling heat transfer from horizontal cylinder to liquid by movable particles

This paper presents a series of experimental results on a passive augmentation technique of boiling heat transfer by supplying solid particles in liquid. A cylindrical heater 0.88 mm in diameter is placed in saturated water, in which a lot of mobile particles exist, and the nucleate and film boiling heat transfer characteristics are measured. Particle materials used were alumina, glass, and porous alumina, and the diameter ranged from 0.3 mm to 2.5 mm. Particles are fluidized by the occurrence of boiling without any additive power, and the heat transfer is augmented. The maximum augmentation ratio obtained in this experiment reaches about ten times the heat transfer coefficient obtained in liquid alone. The augmentation ratio is mainly affected by the particle material, diameter, and the height of the particle bed set at no boiling condition. The augmentation mechanism is discussed on the basis of the experimental results. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 28–41, 2002     

Investigation of Enhanced Boiling Heat Transfer from Porous Surfaces

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强润湿性液体池沸腾传热的实验研究和机理分析

对强润湿性液体的池沸腾传热实验而言，本文提出了行之有效的实验程序，并严格按照实验程序进行了R113池沸腾传热的实验研究，具体研究了表现老化和液体过冷度对池沸腾传热曲线及起沸点的影响，实验中观察到了三个反常现象，最后，从强润湿性液体的沸腾传热机理的角度对其给出了相应的解释。     

水平窄空间沸腾传热的实验研究

通过对五种尺寸的窄空间试验元件分别以水和乙醇做工质进行实验。研究了窄空间间距、窄空间尺寸、不同工质及不同热流密度对窄空间沸腾性能的影响。结果表明：当窄空间尺寸与热流通等因素组合恰当时。其换热系数可比大空间池沸腾提高3～6倍；临界热流密度有所降低。     

Zero‐flux zone model analysis of a single bubble in boiling liquid

We start from a bubble, the basic unit of boiling, to explore liquid boiling. Research indicates that the heat and mass transfer between liquid and vapor is the determinant factor of boiling heat transfer. We have analyzed interfacial vaporization and condensation of a single bubble in boiling liquid based on a zero‐flux zone model. We have deduced the expression of zero‐flux angle and discussed the relationship between zero‐flux zone and the other parameters in order to comprehend the mechanism of boiling heat transfer. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 249–256, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10026     

Behavioral study of alumina nanoparticles in pool boiling heat transfer on a vertical surface

Experiments were carried out to investigate the pool boiling of alumina‐water nanofluid at 0.1 g/l to 0.5 g/l of distilled water, and the nucleate pool boiling heat transfer of pure water and nanofluid at different mass concentrations were compared at and above the atmospheric pressure. At atmospheric pressure, different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer. The effect of pressure and concentration of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. The heat transfer coefficient of 0.5 g/l alumina‐water nanofluid was compared with pure water and clearly indicates deterioration. At all pressures the heat transfer coefficients of the nanofluid were lower than those of pure water. Experimental observation revealed particles coating over the heater surface and subsequent SEM inspection of the heater surface showed nanoparticles coating on the surface forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, investigation was done by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, surface roughness of the heater surface confirmed it. Based on the experimental investigations it can be concluded that an optimum thickness of nanoparticles coating favors an increase in heat flux. Higher surface temperature due to the presence of nanoparticles coating results in the deterioration of boiling heat transfer. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20365     

水平窄空间沸腾换热的数理模型研究

窄空间只有在间距小于汽泡脱离直径时，对沸腾传热强化才有比较显的效果。窄空间沸腾强化传热的机理在于较大的泡底微层加速了蒸发传热和窄空间中被加热的液体周期性地与池液进行容积交换。水平圆盘窄空间中的汽泡生长分为性质完全不同的自由生长期和抑制长大期；在一个周期内，加热面的总传热量等于壁面传导给窄空间液体的热量与通过合体泡底微层蒸发潜热之和。在对圆形水平窄空间的沸腾传热的现象和机理进行分析的基础上，提出了窄空间的沸腾换热过程的数理模型；进而对窄空间沸腾的本质规律在理论上进行了初步探索，并得到分析解。理论计算结果与实验数据比较表明，该分析解适合于中低壁面过热度的情形。由于问题的复杂性，该模型仍需不断完善。