共查询到20条相似文献,搜索用时 125 毫秒
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
采用耦合电场模型的相变格子Boltzmann模型,数值研究了电场作用下锥翅结构表面的饱和池沸腾换热.为了定量分析电场对锥翅结构表面沸腾换热影响的机理,首先在无电场作用下对比调查了平滑表面和锥翅表面的沸腾换热现象.发现锥翅结构在核态沸腾阶段有更多的成核点,沸腾换热性能增强,临界热流密度(critical heat flux,CHF)提高.而在过渡沸腾阶段以及膜态沸腾阶段,由于锥翅结构增加了锥翅表面流体的流动阻力,阻碍了气液交换,换热性能低于平滑表面.基于以上发现,通过对锥翅表面池沸腾过程施加电场,进一步强化了锥翅表面沸腾换热.结果表明,在起始核态沸腾阶段,电场的存在稍微延后了气泡开始成核时间,气泡尺寸减小,沸腾轻微被抑制;充分核态沸腾阶段,由于电场力的作用以及电场与锥翅结构协同表现出的尖端效应,阻止了加热表面干斑的扩散和蔓延,促进沸腾换热;过渡沸腾以及膜态沸腾阶段,尖端效应更加明显,逐渐增大的电场强度使沸腾在更高过热度下处于核态沸腾状态,沸腾换热性能大幅度提高,且CHF逐渐提高. 相似文献
11.
12.
This study presents new data on nucleate boiling heat transfer obtained in compact horizontal tube bundles with small tube gaps. The experiment investigates the heat transfer enhancement effects by the restricted spaces comprising the compact tube bundles and the enhanced heat transfer tubes for nucleate boiling heat transfer of R-11 at atmospheric pressure. A roll-worked tube was used as a new type of enhanced heat transfer tube. The experimental results show that the small tube gaps can greatly enhance boiling heat transfer in a smooth tube bundle, while enhancement effects of small gaps were not quite significant for the enhanced tube bundle. There is a compound effect from the enhanced surface and the restricted space only for the enhanced tube bundle with the tube gap of 0.5 mm. The effects of the tube positions within both compact tube bundles on the boiling heat transfer were minor. 相似文献
13.
Experimental research is performed on two-phase flow boiling heat transfer in micro-channels. FC-72 is used as the working fluid. In order to analyze the heat transfer mechanism during two-phase flow boiling, the dimensionless parameters, e.g., boiling number and convection number, are used, and the effect of these parameters on the heat transfer can be confirmed during flow boiling in the micro-channel. In addition, the transition criterion from bubbly/slug flow to annular flow is proposed from the modified Weber number. Based on the boiling heat transfer mechanism obtained from the experiments, a new correlation is proposed to predict the heat transfer coefficient. The new correlation predicts well the experimental results within a mean absolute error of 5.2%. 相似文献
14.
15.
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
16.
In this article, an experimental investigation is performed to measure the boiling heat transfer coefficient of water flow in a microchannel with a hydraulic diameter of 500 μm. Experimental tests are conducted with heat fluxes ranging from 100 to 400 kW/m2, vapor quality from 0 to 0.2, and mass fluxes of 200, 400, and 600 kg/m2s. Also, this study has modified the liquid Froude number to present a flow pattern transition toward an annular flow. Experimental results show that the flow boiling heat transfer coefficient is not dependent on mass flux and vapor quality but on heat flux to a certain degree. The measured heat transfer coefficient is compared with a few available correlations proposed for macroscales, and it is found that previous correlations have overestimated the flow boiling heat transfer coefficient for the test conditions considered in this work. This article proposes a new correlation model regarding the boiling heat transfer coefficient in mini- and microchannels using boiling number, Reynolds number, and modified Froude number. 相似文献
17.
18.
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
19.