Effect of inclination angle on the condensation of R134a inside an inclined smooth tube

Abstract

Almost all work on condensation in tubes were conducted for smooth tubes in a horizontal or vertical orientation, and little has been done at other inclination angles. Recent experimental works with condensation at different inclination angles showed that the pressure drops were a function of inclination angle. It was therefore the purpose of this paper to numerically investigate the pressure drop of condensation inside a smooth tube at different inclination angles, and to give additional perspectives and insight to previous experimental works. The case study investigated was a smooth tube with an inner diameter of 8.38 mm and a length of 1488 mm. The condensing fluid was R134a and the saturation temperature was 40 °C. Simulations were conducted at a heat flux of approximately 5 kW/m2, at mass fluxes of 100–600 kg/m2 s, and the inclination angles were varied from vertical downward to vertical upward. The Volume of Fluid (VOF) multiphase flow formulation was used and ANSYS FLUENT was used as solver of the governing equations. The predicted results showed a good agreement with experimental data. It was found that the effect of inclination angle on pressure drop and void fraction became negligible at high mass fluxes and vapour qualities. The pressure drop increased as the void fraction increased. The pressure drops also increased when the mass fluxes increased. These increases were more significant at high vapour qualities.