BUOYANCY-AFFECTED LAMINAR-FILM CONDENSATION

The flow and heat transfer in a laminar condensate film on an isotherm al vertical plate is modelled mathematically. The strict Boussinesq ap proximation is adopted to account for buoyancy due to local temperatur e variations within the film. A similarity transformation reduces the governing boundary-layer type equations to a coupled set of ordinary d ifferential equations and the resulting three-parameter two-point boun dary value problem is solved numerically for Prandtl numbers, Pr, rang ing from 0.001 to 1000 and Jakob numbers, Ja, between 0.0001 and 1.5. The principal effects of the favourable buoyancy are to reduce the thi ckness of the condensate film and increase the film velocity at the sm ooth liquid-vapour interface, whereas the friction and heat transfer a t the plate are enhanced. In accordance with the classical Nusselt the ory, it is found that the temperature varies nearly linearly across th e film. The computed similarity profiles for velocity reveal, however, substantial departures from the parabolic distribution assumed in the simplified Nusselt analysis.