Modeling of mixed-convection laminar film condensation from mixtures of a vapor and a lighter noncondensable gas

Abstract

The effects of a lighter noncondensable gas on laminar film condensation from moving vapor-gas mixtures was investigated. Condensation occurred on the top of an isothermal flat plate with an arbitrary inclination. The liquid film and the mixture boundary layers were described with the conservation equations for mass, momentum, energy, and gas species (for the mixture boundary layer only). A finite volume method was applied on a staggered grid in the numerical solution domain. The properties for both liquid and mixture were evaluated at the local temperature. The solution procedure was terminated either when the separation criteria were met or when the flow reached the transition to turbulence. The main objectives of the study were to investigate the mixture boundary layer separation distance and the reduction in heat transfer to the wall due to the presence of a lighter noncondensable gas. Three vapor-gas combinations were studied: steam-hydrogen, Freon12-air, and mercury-air. Applying two simple collapsing procedures, a set of graphs is presented for each vapor-gas combination which can be used to estimate the separation length for a given set of input parameters. For each mixture and for a given free stream temperature, the variation of Nusselt number (normalized by the square root of the local Reynolds number) along the plate is also presented for different values of gas concentration and wall temperature. (Abstract shortened by UMI.)