Heat transfer during the condensation of R134a inside eight parallel microchannels

In this study the local heat transfer coefficient was investigated experimentally during the convective condensation of R-134a inside eight round (diameter D = 0.77 mm) horizontal and parallel microchannels. The test conditions included the pressure p, the vapor quality x(v), the heat flux q and the mass velocity G ranging from 7.3 to 9.7 bar, 0.55 to 1, 17 to 53 kW m(-2), and 230 to 445 kg m(-2) s(-1), respectively. The influence of temperature, heat flux, mass velocity and quality on the heat transfer coefficient, h, was evaluated. The results show that mass velocity and vapor quality have an important influence on the heat transfer coefficient. The consideration that all of the resistance to heat transfer is due to the conduction through the liquid film is a good approximation, mainly for x(v) < 0.95. The experimental results were comparable with correlations and semi-empirical models described in the literature. (C) 2012 Elsevier Ltd. All rights reserved.