An analysis method based on two-phase boundary layer analysis has been developed to study the effects of superimposed forced convection on natural convection steam-gas flow condensing along a vertical plate. The mechanism by which superimposed forced convection enhances heat transfer is evaluated: the bulk flow blows away non-condensable gases accumulating near the interface, resulting in an elevated condensation driving force. Further. this bulk flow blowing capability may be characterized by a conventional mass transfer driving potential. Results of the new model are shown to be consistent with experimental data. Finally, a simple criterion was developed to identify transition to mixed convection from natural convection steam-gas flow. (c) 2008 Elsevier Ltd. All rights reserved.