Liquid film condensation from water vapour flowing downward along a vertical tube

This paper focuses on a numerical study of the liquid film condensation from the vapour-gas mixtures inside a vertical tube. The model uses an implicit finite difference method to solve the governing equations for liquid film and gas flow together including the boundary and interfacial matching conditions. The external wall of the tube is subjected to a constant temperature or uniform heat flux. The influence of the inlet conditions of the gas mixtures and the tube length on the heat and mass transfer are analyzed. The results indicate that an increase of the relative humidity and the inlet-to-wall temperature enhance the condensation process. Increasing the tube length produces a high amount of condensed vapour along the tube. Additionally, non-condensable gas is a decisive factor in diminishing the efficiency of the heat and mass exchanges. For a fixed heat flux, increasing the inlet temperature substantially increased the accumulated condensation rate. Overall, these parameters are relevant factors to improve the effectiveness of the thermal and desalination systems. (C) 2017 Elsevier B.V. All rights reserved.