Condensing Heat Transfer Coefficients for R134a at Different Saturation Temperatures in Inclined Tubes

Abstract

This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth copper tube of inner diameter of 8.38 mm. Experiments were conducted for inclination angles ranging from −90° (vertical downward) to +90° (vertical upward) for mass fluxes between 100 kg/m2s and 400 kg/m2s and vapour qualities between 0.1 and 0.9 for saturation temperatures ranging between 30 °C and 50 °C. The results show that saturation temperature and inclination angles strongly influence the heat transfer coefficient. With respect to saturation temperature, an increase in saturation temperature generally leads to a decrease in heat transfer coefficient irrespective of the inclination angle. The effect of inclination angle was found to be more pronounced at mass fluxes of 100 kg/m2s and 200 kg/m2s for the range of vapour qualities considered. Within the region of influence of inclination there is an optimum angle which is between 15° and −30° (downward flow). The inclination effect corresponds to the predominance of the effect of gravity on the flow distribution.