Data obtained by numerical solution of boundary-layer flow, energy and diffusion equations for laminar and turbulent flows of humid air are described. The effect of vapor concentration and vapor-gas mixture temperature on the intensity of and similarity between the heat- and mass-transfer processes in the presence of surface vapor condensation is considered. It is shown that the Reynolds analogy is valid in the range of mass vapor concentration in the flow core C-10 < 0.2. In the region of higher vapor concentrations (condensation of a vapor with incondensable species), the analogy between the transfer phenomena is violated and the assumption that Le = 1 can no longer be used. (C) 2003 Elsevier Ltd. All rights reserved.