Condensation heat transfer coefficients and enhancements of R134a in smooth and microfin inclined tubes

Abstract

This paper presents the thermal performance of smooth and microfin tubes and the enhancement factors as they respond to inclination angle, mass flux and vapour quality in inclined tubes of 1.488 m long, 9.55 mm outer diameter during the convective condensation of R134a at the saturation temperature of 40oC. For the experiment, the quality was varied between 0.5 and 0.9, mass flux of 200 kg/m2s to 400 kg/m2s and inclination angle between -90o (vertically downward) and +90o (vertically upward) tube orientations. The result shows that inclination angle, mass flux and vapour quality significantly affect the heat transfer coefficient and enhancement factor. The enhancement factor varied between 0.98 and 2.0 depending on the operating variables. Higher enhancements were however obtained during the downward flow as compared with upward flow.