Heat and mass transfer in a channel with surface mass addition: Application to phase change processes

The heat and mass transfer processes in a binary mixture flowing in a parallel plate channel with mass addition at the bounding surfaces are investigated analytically. The rate of mass addition, the temperature, and the mass fraction are arbitrarily prescribed at each of the bounding walls. Similarity solutions are evaluated numerically to yield pressure gradient, Nusselt number, and Sherwood number results for a wide range of each of three governing parameters. It is found that increasingly strong surface mass addition markedly increases the magnitude of the axial pressure gradient. Mass addition decreases the Nusselt and Sherwood numbers at the channel wall at which the injection is strongest but may actually increase these moduli at the opposite wall. A generalizing analysis is performed to accommodate phase change processes as well as to accommodate the specification of plenum conditions rather than wall surface conditions. Application is made to the evaporation of liquid water by an air stream. It is shown that the rate of evaporation is augmented as the rate of air injection increases, but the extent of the augmentation is less than the causative increase in the air flow rate.