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文中对颗粒烧结多孔表面和泡沫金属多孔表面上的液氮池沸腾换热特性进行了实验研究,并与光滑铜表面的试验结果进行了比较。结果表明,多孔表面成核条件更好,使得沸腾起始点相对于光滑表面提早;随着热流密度逐渐增大,气泡增多,且在多孔层内部连成一片,加热表面气泡离开受到多孔层的限制,热阻增加,换热系数大幅降低,整个沸腾进入表面沸腾阶段;多孔结构所产生的毛细抽力不断补充冷却流体,使表面沸腾能够持续较长时间,实验中未观测到临界热流密度现象。在实验基础上,文中描述了多孔表面不同池沸腾换热阶段的主要换热机理,并分析了流体工质、多孔层厚度、渗透系数、孔隙率等参数对多孔表面池沸腾换热的影响。 相似文献
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本文将“米”字形放射状槽道强化面积大、气泡脱离阻力小与毛细芯成核位点多等优点相结合,设计加工出一系列铜基放射状槽道与烧结毛细芯耦合散热表面,在10 K、20 K和30 K三个不同过冷度下进行了HFE-7100池沸腾换热实验,得到不同表面在不同过冷度条件下的沸腾换热性能。结果表明,槽深对换热影响较大,耦合毛细芯的铜基散热结构可以进一步提高临界热流密度和换热系数。最大临界热流密度和换热系数分别可达130.1 W/cm2和0.94 W/(cm2·K),并对实验过程中的气泡动力学行为进行了分析。 相似文献
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利用宽视场体视显微镜、高速摄影仪以及CCD摄像系统对纯蒸发和沸腾换热情形下竖直矩形毛细微槽内液体的特殊干涸行为进行了观察,对液体沿微槽槽道方向的润湿高度进行了观察测量,并对液体沿微槽槽道方向的相变换热特性进行了实验研究.实验结果表明:竖直矩形毛细微槽群是一种高性能的相变换热强化表面,微槽中液体的蒸发与沸腾对干涸点高度的变化有着复杂的影响,热流密度和相变换热系数沿槽道方向的分布不均匀. 相似文献
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表面活性剂对池沸腾换热的影响 总被引:1,自引:0,他引:1
本文以SDS(十二烷基硫酸钠)为表面活性剂,研究了在不同过冷度下SDS浓度对池沸腾换热的影响.结果表明在低SDS浓度下,沸腾换热在一定热流密度范围内得到显著强化.在不同过冷度下.均存在相应的最佳SDS浓度值,最大换热系数可达纯水的2~4倍.在饱和沸腾状态下,临界热流密度(CHF)随SDS浓度的增加而减小,沸腾曲线呈现三类分歧,且存在"S"型沸腾曲线及较明显的沸腾滞后现象. 相似文献
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本实验提出了复合方柱微结构的亲疏水强化换热表面,并对其在FC-72工质中的池沸腾换热进行研究。实验采用光滑芯片和方柱微结构高效换热PF30-60芯片作为对比组,通过使用装有显微镜头的高速摄像机对微细化沸腾现象进行捕捉。实验及分析结果表明:亲疏水表面芯片可有效提高沸腾的临界热流密度,降低沸腾起始点对应的壁面过热度,同时在相同热流密度下其壁面温度较PF30-60降低6~9 K;由于微结构区域提供数目可观的汽化核心,不断生长滑移的汽泡被困在光滑亲水通道,在亲水面及两侧微结构作用下加速汽泡的生长合并与脱离,因此沸腾换热效果得到显著提高。 相似文献
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微槽道中纳米流体沸腾换热特性研究 总被引:2,自引:0,他引:2
为研究纳米流体在微槽道中的沸腾换热特性及规律,分别以去离子水和体积浓度为0.2%、0.5%的水基Al2O3纳米流体为工质进行试验,研究质量流速、热流密度、进口过冷度、槽道尺寸等因素对沸腾传热系数的影响及其两相摩擦压降与出口干度的关联分析和沸腾换热关联式对比拟合.试验结果表明:在一定热流密度和质量流速下,传热系数随槽道尺... 相似文献
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A. N. Pavlenko V. P. Koverda A. V. Reshetnikov A. S. Surtaev A. N. Tsoi N. A. Mazheiko K. A. Busov V. N. Skokov 《Journal of Engineering Thermophysics》2013,22(3):174-193
This paper represents results on investigating the dynamics of boiling and disintegration of superheated liquid films and jets. The first part deals with experimental study of boiling liquid outflow through short cylindrical and slit channels. Evolution of disintegration of a hot water jet flow is observed both at low and moderate superheating and at high and limit superheating, and also for vaporization mechanisms corresponding to these superheatings. Peculiarities of disintegration of jets through slit and cylindrical channels are noticed. Results on measuring the reactive thrust of the jet through a slit channel under different geometrical conditions behind the channel outlet are represented. The 1/f fluctuations in transient regimes of superheated liquid boiling and in transient regimes of behavior of the jet shape are found. The second part of this article represents results on experimental investigation of nonsteady heat transfer and dynamics of the development of crisis phenomena at boiling of a falling subcooled liquid film in the conditions of stepwise heat release. The experimental data were obtained using synchronized high-speed infrared thermography and video. It is shown that with growth and condensation of vapor bubbles, on the liquid film interface appear large-amplitude waves that lead to considerably increasing local intensity of heat transfer. New data on the boiling incipience temperature in a subcooled liquid film, depending on the heat flux density, are obtained. It is found that the development of boiling crisis is a result of appearance of local dry patches and their subsequent growth by the mechanism of longitudinal thermal conductivity in the heat transfer wall as the equilibrium heat flux density is exceeded. 相似文献
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1引言微小空间内的沸腾在电子器件冷却、航天热控、微型换热器以及核反应堆的冷却等领域中有着广泛的应用,因此对其沸腾机理的研究具有重要的意义。过去微小空间内的沸腾研究主要是针对光滑表面[‘-‘1,已证明在微小空间里,沸腾换热受空间尺寸的影响要比大空间大。对于多孔表面在微小空间内的沸腾研究则相对较少。本文对矩形槽道表面和烧结型多孔表面在微小空间里的沸腾进行了实验研究。2实验装置实验装置如图1,实验段是3O0mm长的紫铜管(包括矩形槽道管和烧结型的多孔管),内插不同外径的不绣钢管,形成不同间隙的环形小空间。在内… 相似文献
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The article presents the results of experimental investigation of boiling heat transfer of refrigerant R-21 in upward flow in a vertical plate-fin heat exchanger with transverse size of the channels that is smaller than the capillary constant. The heat transfer coefficients obtained in ranges of small mass velocities and low heat fluxes, which are typical of the industry, have been poorly studied yet. The characteristic patterns of the upward liquid-vapor flow in the heat exchanger channels and the regions of their existence are detected. The obtained data show a weak dependence of heat transfer coefficient on equilibrium vapor quality, mass flow rate, and heat flux density and do not correspond to calculations by the known heat transfer models. A possible reason for this behavior is a decisive influence of evaporation of thin liquid films on the heat transfer at low heat flux. 相似文献
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FC-72在竖直壁面上及微小三角型通道内的沸腾传热 总被引:1,自引:0,他引:1
本文对浸在FC-72液池中的竖直壁面及两个微小三角形通道进行了沸腾实验研究,考虑了管道尺寸对沸腾传热特性的影响。两个微小三角形通道的边长分别为1.5和2.5 mm,水力直径分别为0.87和1.44 mm,长度50 mm,采用铜块上开V型沟槽,再覆盖上透明的玻璃片构成。热流密度由贴在铜块背后的膜状加热器提供。实验得到了沸腾曲线和传热系数,并用DV摄影机拍摄到了沸腾状况。实验结果显示,管道尺寸对沸腾传热特性有显著的影响,CHF值随通道尺寸的减小而减小,小通道在低热流密度时传热系数较大。 相似文献
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The flow boiling heat transfer of water in a microchannel heat sink with variable initial vapor quality at the inlet is investigated.
The stainless steel microchannel heat sink contains ten 640 × 2050 μm channels with a length of 120 mm; the wall roughness
is 10 μm. The data on the local heat-transfer coefficient distribution in heat sink length are obtained in the range of mass
fluxes from 30 to 90 kg/m2s, heat fluxes from 40 to 170 kW/m2, and vapor qualities from 0 to 1. The heat transfer instability associated with dry spots resulting from insufficient wetting
of channel walls introduces substantial contribution to the heat transfer mechanism and leads to decreasing heat transfer
in heat sink length downward the flow. The developed method for calculating the flow boiling heat transfer of water in a microchannel
heat sink allows more accurate prediction of heat transfer drop than available methods. 相似文献
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在前文[1]实验研究的基础上,利用带液池的多孔壁微热虹吸蒸发段模型,对颗粒多孔薄层在真空状态下的沸腾两相流与传热进行了分析,综合实验数据,建立了传热关联式。 相似文献
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An experimental investigation was carried out on the boiling heat transfer characteristics of water and R-11 on the outside of a horizontal heated tube in narrow spaces. Two kinds of heat transfer surfaces (roll-worked and smooth surfaces) were tested. The test section consisted of a narrow annular space formed by enclosing the heated tube in an isolated concentric outer tube with two horizontal slats on the top and bottom. The nucleate boiling heat transfer characteristics were investigated experimentally at atmospheric pressure. The experimental results indicated that a single roll-worked tube in bulk liquid showed better boiling heat transfer than a single smooth tube. In the narrow spaces, the boiling heat transfer coefficients for the smooth tube were considerably enhanced when the gap size was so selected as to take an optimum value. There was no clear optimum gap size for heat transfer enhancement for the roll-worked tube in the narrow spaces. Enhancement of boiling heat transfer in the narrow spaces for the roll-worked tube was not clearly observed in this experiment. Finally, the critical heat flux (CHF) for boiling heat transfer in narrow spaces can be predicted by using a proposed CHF correlation. 相似文献