This paper describes the results of enhancement in heat transfer with a two-phase flow of refrigerant 22 under evaporating conditions. In order to enhance the heat transfer, two kinds of tube were tested: a tube with a microporous internal surface, which was made by fixing copper particles on a smooth copper surface by plating with copper, and a smooth-inner-surface tube into which a microporous, thin plate fin was inserted.

The experimental results show that the heat-transfer coefficient of the microporous tube is 7.5 times as large as that of a smooth tube, and the heat-transfer coefficient of the microporous finned tube is from 1.65 to 1.85 times as large as that of a smooth finned tube for incomplete evaporation.