润滑油对小管径光管内R410A流动沸腾流型及换热特性的影响

Effect of Oil on Flow Pattern and Heat Transfer Characteristic of R410A Flow Boiling inside Small Diameter Smooth Tubes

实验研究了R410A-油混合物在5.0 mm光管内流动沸腾的流型及换热特性。实验结果表明,润滑油延迟流型向环状流和干涸流的转化,实验得出的流型与基于混合物性的流型图吻合较好;纯制冷剂R410A的换热系数随干度的增大先增大后减小,峰值出现在干度为0.7~0.8左右;对于R410A-油混合物,在干度小于0.6的工况下,油的存在总是增强换热,在干度为0.7时,换热系数随油浓度的增大先增加后减小;在干度大于0.8情况下,换热系数随油浓度和干度的增大迅速降低。在本文得出的5.0 mm光管实验数据和已有文献关于7.0 mm光管内的实验数据基础上,开发了基于流型和混合物性的流动沸腾换热关联式,新关联式可以很好地预测不同管径光管内的流动沸腾换热特性。

Experimental study of flow patterns and heat transfer characteristics of R410A-oil mixture flow boiling inside a smooth tube with outside diameter of 5.0 mm is performed. The test results showed that, the presence of oil may retard the transformation of flow patter to annular flow and dryout flow, and the observed flow patterns match with the new flow pattern map based on the mixture properties very well;the heat transfer coefficient of the R410A initially increases with vapor quality and then decreases, presenting a local maximum in the vapor quality range between 0.7 and 0.8;the presence of oil enhanced the heat transfer coefficient when the vapor quality is less than 0.6;when the vapor quality is about 0.7, the heat transfer coefficient initially increases and then decreases with the increase of oil concentration; when the vapor quality is higher than 0.8, the heat transfer coefficient decreases rapidly with increasing nominal oil concentration and vapor quality. Based on the experimental data for 5.0 mm smooth tube obtained in the present study and those for 7.0 mm smooth tube obtained in the existing research, a new heat transfer coefficient correlation of R410A-oil mixture flow boiling inside small diameter smooth tube is developed by reflecting the flow pattern and the mixture properties. The new correlation can agree well with the heat transfer characteristics of R410A-oil mixture flow boiling in smooth tubes with different diameters.