Change in wetting characteristic of heated refrigerant in falling film evaporation

作者：Lu, Xingbin; Liu, Jinping^*; Xu, Xiongwen; Chen, Jianxun

来源：International Journal of Refrigeration, 2020, 117: 198-208.

DOI：10.1016/j.ijrefrig.2020.04.005

• Refrigerant
• Micro-layer evaporation
• Contact line behaviour
• Rivulet
• Falling film evaporation

The wetting area plays a critical role in falling film evaporation. In the falling film evaporation process, the refrigerant is observed to shrink to a narrow rivulet when heated at a low temperature difference. In this study, a new model based on the stable rivulet and micro-layer evaporation theories was built to explain this phenomenon. A falling film evaporation experiment was conducted with R134a to examine the accuracy of the model. The calculation of the rivulet's width has good agreement but a little smaller than the experiments. Moreover, the theoretical analysis shows that the thermal-capillary effect will intensify the shrinkage of the rivulet, but the apparent contact angle change in the heated refrigerant is mainly caused by the evaporation of the micro-film. The decreased cross section of the rivulet will also attribute to the shrinkage. In conclusion, although the changed contact angle is small, the reduction of the wettability of refrigerant in falling film evaporation process cannot be neglected.