Analysis of the effects of mass transfer on heat transfer in the process of moisture exchange across a membrane

A theoretical study was conducted to investigate the effects of mass transfer on heat transfer in the process of moisture exchange across a membrane and a mathematical model describing the heat transfer with consideration of the effect of mass transfer was developed. A dimensionless variable, ψ_i, which presents the degree to which the mass transfer affects the heat transfer, was proposed through theoretical analysis. With calculating of this dimensionless variable, the heat transfer coupled with mass transfer can be converted into a conventional heat transfer, making the heat transfer calculation simpler and more easily to understand. On the basis of theoretical analysis, the effects of mass transfer on heat transfer were numerically studied. The results show that, in the case that the temperature gradient and mass transfer are in the same direction, ψ_i is greater than unity, and the mass transfer acts to enhance the heat transfer; in the case that the temperature gradient and mass transfer are in opposite directions, ψ_i is less than unity, and the mass transfer works to hinder the heat transfer. When the mass flux is small, the effect of the mass transfer is weak. When the mass flux is large, the heat flux carried by the mass flux has a considerable impact on the heat flux, and ψ_i, deviates from unity significantly.