Coupled heat and mass transfer of a stagnation point flow in a heated porous bed with liquid film evaporation

An analytical solution is presented for the study of coupled heal and mass transfer in a stagnation point flow of air through a heated porous bed with thin liquid film evaporation. The analysis indicates that the coupled heat and mass transfer process in the air stream induced by the evaporation of a thin liquid water film embedded in the porous medium of a given porous ma terial is governed by the Peclet number Pe, the Lewis number Le, the porosi ty of the porous bed phi, as well as the ambient temperature T-infinity and relative humidity phi of air. It is shown that the heat transfer between t he heated plate and the air stream is predominated by the transport of the latent heat associated with the thin liquid film evaporation. The analysis also demonstrates that the air stream with a lower relative humidity, a hig her temperature, and a higher Peclet number lead to an increase of heat tra nsfer rate. For the case when Le > 1, the mass transfer rate is enhanced wh ile the heat transfer rate is reduced. These findings are of significance f or the design of a cross-flow indirect evaporative air cooler. (C) 1998 Els evier Science Ltd. All rights reserved.