Experimental study on condensation heat transfer of R32, R152a and R22 in horizontal minichannels

The heat transfer characteristics of R32, R152a and R22 during condensation were experimentally investigated in a circular (d(h) = 1.152 mm) and two square (d(h) = 0.952 and 1.304 mm) horizontal minichannels. The experiments used saturation temperatures from 30 degrees C to 50 degrees C, mass fluxes from 200 to 800 kg/(m(2) s) and vapor qualities from 0.1 to 0.9. The experiments investigated the effects of the flow conditions (mass flux, vapor quality, saturation temperature and coolant inlet temperature), the channel diameter, the channel geometry and the thermophysical properties on the heat transfer coefficients. The results show that the heat transfer coefficients increase with increasing mass flux and vapor quality and decreasing saturation temperature and channel diameter. The coolant inlet temperature has little effect on the experimental results. The heat transfer coefficients in the square minichannel are enhanced by the surface tension for vapor qualities less than 0.5 compared with that in the circular minichannel. The study shows that R32 and R152a are good substitutes for R22 based on the condensation heat transfer characteristics. Condensation heat transfer correlations and a theoretical solution are used to predict the experimental data in this study. (C) 2015 Elsevier Ltd. All rights reserved.