This paper concerns a numerical analysis of the evaporation of water in pure air, humid air and superheated steam in an externally insulated channel. Results were obtained for mixed and free convection driven by combined thermal and mass buoyancy forces. For natural convection case, the analysis is restricted to situation in which combined buoyancy forces act in the downward direction. The results show that below a certain temperature of the free stream, water evaporation rate decreases as the humidity of air increases and above it this relation reverses. This temperature "inversion point temperature" was treated in previous experimental and numerical studies in the case of forced convection. In this work, particular attention is paid to study the effect of the ambient conditions on evaporation rate of water and the inversion temperature phenomenon in the condition of free and mixed convection. (C) 2003 Elsevier Ltd. All rights reserved.