Film condensation along an inclined surface in a porous medium

Abstract

The problems of steady film condensation outside a wedge or a cone embedded in a porous medium filled with a dry saturated vapor are investigated. As in classical film condensation problems, it is assumed that (a) the condensate and the vapor are separated by a distinct boundary with no two-phase zone in between, and (b) the condensate has constant properties. Within the boundary layer approximations, similarity solutions have been obtained for the temperature and flow fields in the condensate. Moreover, a closed form solution has been obtained for the Nusselt number which depends on the square root of the Rayleigh number and the dimensionless film thickness. The latter is found to be a function of a dimensionless parameter related to the degree of wall subcooling. Asymptotic cases for small and large wall subcoolings are also considered. As in the classical film condensation problems, it is found that the ‘Nusselt’-type approximation (for small wall subcooling) overestimates the film thickness while underestimates the Nusselt number. An approximate expression for Nusselt number in terms of the degree of wall subcooling explicitly is also obtained.