Influence of oil concentration on wetting behavior during evaporation of refrigerant-oil mixture on copper surface

As wetting behavior is a key factor affecting boiling heat transfer performance of refrigerant-oil mixture, the influence of oil concentration on wetting behavior during evaporation of refrigerant-oil mixture on copper surface was experimentally investigated. The wetting behavior was analyzed by capillary rise method, and the test conditions covered oil concentrations of 1, 3, 5 and 10 wt%, and surface roughness of 0.028, 0.079, 0.144, 0.419 and 1.166 mu m. The experimental results show that protuberant liquid film occurs in front of meniscus during evaporation of refrigerant-oil mixture; and contact line velocity, contact angle, liquid film length and rising liquid height increase as oil concentration increases. It is also found that the ratio of the rising liquid height of refrigerant-oil mixture to that of pure refrigerant is larger than 1, and ranges between 1.42 and 2.18 under present test conditions, indicating that the presence of oil significantly enhances the surface wettability of refrigerant. (C) 2015 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.