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Prediction of Heat Transfer Coefficients for Flow Boiling of Refrigerant-Oil Mixtures in Horizontal Evaporator Tubes

水平蒸发管内冷冻油混合物流动沸腾传热系数的预测

基本信息

批准号：
63550167
负责人：
YOSHIDA Suguru
金额：
$ 1.34万
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：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

1. Experiments and theoretical analyses were carried out on the heat transfer to Refrigerant-22 with 0 to 6 percent by mass of oil contained, flowing in horizontal smooth evaporator tubes. Following results were obtained. (1) The addition of oil produced an increase in heat transfer coefficient over a wide range of quality at low mass velocities and in the low quality region at high mass velocities because of an intensive foaming action. (2) The heat transfer coefficient decreased in the high quality region at high mass velocities, where an annular flow prevailed. This reduction of the heat transfer coefficient was attributed to a deterioration in local heat transfer near the tube top due to the formation of oil-rich and thereby highly viscous liquid film. (3) When the heat flux is low at a high mass velocity, the circumferentially averaged heat transfer coefficient for refrigerant-oil mixtures can be evaluated from a correlation equation for pure refrigerants by using the liquid properties of the mixtures. At a low mass velocity or at a high heat flux and high mass velocity, however, the circumferential variation of the oil mass fraction in the liquid film must be taken into account to predict the circumferentially averaged heat transfer coefficient.2. Following results were experimentally obtained for refrigerant-oil mixtures in a horizontal, spirally grooved evaporator tube. (1) The addition of the oil generally deteriorated the heat transfer, but improved in low quality region at high mass velocities and high heat fluxes. The deterioration was more remarkable with increasing quality and oil mass fraction. (2) The heat transfer enhancement at a low mass velocity was reduced by two-thirds of that for oil-free refrigerant. When the mass velocity, heat flux and oil mass fraction were high, the heat transfer was considerably enhanced in high quality region.

1. 对含油量为0 ~ 6%的水平光滑蒸发器管内制冷剂-22的传热进行了实验和理论分析。得到以下结果：(1)由于剧烈的起泡作用，油的加入在低质量速度下的大质量范围内和在高质量速度下的低质量区域产生了传热系数的增加。(2)在高质量流速下，高质量区换热系数减小，以环形流为主。传热系数的降低是由于管内顶部附近的局部传热恶化，这是由于富油形成的高粘性液体膜造成的。(3)在高质量速度下，当热流密度较低时，利用制冷剂-油混合物的液体性质，可以由纯制冷剂的相关方程计算出制冷剂-油混合物的周向平均换热系数。然而，在低质量速度或高热流密度和高质量速度下，必须考虑液膜中油质量分数的周向变化，以预测周向平均传热系数。下面的实验结果得到了制冷剂-油混合物在水平，螺旋槽蒸发器管。(1)在高质量速度和高热流密度下，油的加入一般会使传热恶化，而在低质量区域则会有所改善。随着质量和油质量分数的增加，变质更为显著。(2)低质量速度下的换热强化比无油制冷剂降低了2 / 3。当质量速度、热流密度和油质量分数较高时，高质量区域的换热效果明显增强。