A detailed numerical study has been conducted in order to analyse the combined buoyancy effects of thermal and mass diffusion on the turbulent mixed convection tube flows. Numerical results for air-water system are presented under different conditions. A low Reynolds number k-epsilon turbulent model is used with combined heat and mass transfer analysis in a vertical heated tube. The local heat fluxes, Nusselt and Sherwood numbers are reported to obtain an understanding of the physical phenomena. Predicted results show that a better heat transfer results for a higher gas flow Reynolds number Re, a higher heat flux q(w) or a lower inlet water flow Gamma(0). Additionally, the results indicate that the convection of heat by the flowing water film becomes the main mechanism for heat removal from the wall. (C) 2003 Published by Elsevier Science Ltd.