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Prediction of Heat Transfer Coefficient for Flow Boiling in Horizontal Tubes

水平管内流动沸腾传热系数的预测

基本信息

批准号：
61550163
负责人：
YOSHIDA Suguru
金额：
$ 1.41万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

At low mass velocity or low quality in horizontal evaporator-tubes, the heat transfer coefficient is not uniform but varies extermely along the tube perimeter, due to the phase separation with the liquid flowing in the lower part of the tube and the vapor in the upper part. Experimental data of the local heat transfer coefficient along the perimenter of horizontal tubes for boiling R22 were obtained under the conditions of different tube diameters, pressures, mass velocities and heat fluxes in the whole quality region. The separation angle, that is, the angle measured from the bottom point of the horizontal tube to the point of separation between the wet part and the dry part of the inside perimeter, was estimated from the heat transfer data. This angle increased with an increase in mass velocity, increased or decreased with increasing quality depending on the mass velocity, and increased with a decrease in tube diameter or pressure. The characteristics of the circumferentially averaged heat transfer coefficient were explained mainly by the behavior of the separation angle. The correlation proposed previously by the authors for the heat transfer in the annular two-phase flow regime was found to be applicable to the prediction of the averaged heat transfer coefficient over the wet perimeter of the horizontal evaporator-tube, while a well-known heat transfer correlation for singlephase fluid flow was to be applicable to the averaged heat transfer coefficient over the dry perimeter. The circumferentially averaged heat transfer rate in horizontal evaporator-tubes could be predicted by using these correlations of heat transfer coefficients and the measured value of the separation angle.

在低质量流速或低干度条件下，水平蒸发管的传热系数沿管周沿着变化很大，这是由于液体在管的下部流动，而蒸汽在管的上部流动时发生了相分离。在不同管径、不同压力、不同质量流速和不同热流密度条件下，获得了R22水平管沸腾沿周向沿着局部换热系数的实验数据。分离角，即从水平管的底部点到内周的湿部分和干部分之间的分离点测量的角度，从传热数据估计。该角度随着质量速度的增加而增加，随着质量速度的增加而增加或减少，并且随着管直径或压力的减小而增加。周向平均换热系数的特性主要由分离角的行为来解释。作者以前提出的环形两相流传热关联式适用于水平蒸发管湿周平均传热系数的预测，而众所周知的单相流体传热关联式适用于干周平均传热系数的预测。利用这些关联式和分离角的测量值，可以预测水平蒸发管的周向平均传热量。