A theoretical study of the evaporation of water into its own vapour, air and a mixture thereof is presented. The equations describing the coupled heat and mass transfer are set up and solved to find the evaporation rates. The calculated results are in good agreement with published experimental data. The inversion temperature, above which the evaporation rate into pul-e superheated steam is higher than into dry air, is calculated for constant mass and volumetric Hows and compared with published data. Refined definitions of the inversion temperature are introduced which enable a more precise description of the phenomenon and explain the variation in published data. (C) 2000 Elsevier Science Ltd. All rights reserved.