Numerical simulation of condensation inside an inclined smooth tube

In this study the condensation phenomena inside an inclined smooth tube were investigated. The tube internal diameter was 8.38 mm, and its length was 1488 mm. The condensing fluid was R134a at a saturation temperature of 40 °C. The Volume of Fluid (VOF) multiphase-flow formulation was utilized to solve the governing equations of continuity, momentum, energy and turbulence. The flow field was assumed to be unsteady, turbulent and three-dimensional. The fluid properties were considered to be constant as temperature changes were negligible. The effects on heat transfer coefficients of various parameters were investigated. These parameters included tube inclination angle, vapour quality, refrigerant mass flux, and flow regimes. Simulations were conducted at a heat flux of approximately 5 kW/m2, mass fluxes of 100-600 kg/m2·s, while the inclination angles of flow were varied between vertical downward, to vertical upward. The results of the simulations were compared to an experimental database and a good agreement was found with the experimental data. The numerical simulations gave new perspectives and complementary information that was not determined experimentally. The results showed that an optimum downward inclination angle of between −30° and −15° exists, for the heat transfer coefficients.