CFD simulation of air-steam condensation on an isothermal vertical plate

Abstract

This article presents a numerical simulation of the condensation of water vapor with air as the non-condensable gas on an isothermal vertical wall and for inlet mass fraction of the air from 0.05 to 0.5 using the Volume of Fluid (VOF) model of Fluent 6.3 software. The condensation model was used for two-phase, two-dimensional and compressible VOF model and it is suitable for the condensation in presence of additional non-condensable gases on an isothermal vertical plate. All the thermal properties of the water vapor and air were assumed to be functions of temperature and were calculated in user-defined functions (UDF). The source terms including mass source term, energy source term and species source term were also calculated using UDF and hooked to their corresponding conservation equations. The results from the condensation simulation are compared with the experimental results of Dehbi, Uchida and Tagamia from the literature. The condensation simulation results match closely with Dehbi's experimental correlation, and differ with the curve of Dehbi's 6%, which show that the simulation model is reliable. The condensation simulation results show that, the surface normal velocity has a prominent contribution in enhancing the convection heat transfer process, the wall shape should be changed to increase the normal velocity component. The results also show that the change of the mass fraction of the non-condensable gas directly influence the thickness of the condensate film, and then affect the local heat transfer coefficient.