Simplified analysis of coupled heat and mass transfer processes in packed bed liquid desiccant-air contact system

Abstract

One-dimensional model is frequently used to describe the coupled heat and mass transfer processes in the packed bed liquid desiccant dehumidifier/regenerator. In this paper, within relatively narrow range of operating conditions which are usually encountered in practical dehumidification/regeneration processes, the linear approximation was made to find out the dependence of equilibrium humidity ratio on solution temperature. New parameters were defined and the original equations were rearranged to obtain two coupled ordinary differential equations. For the general cases with different values of Lewis factor, approximations of constant properties and coefficients were further made to render the coupled equations linear. Roots of the characteristic equation were determined algebraically and analytical solution to the linear coupled equations was obtained. Analytical expression for the tower efficiency was further developed based on the analytical solution. The way for obtaining the averaged overall heat and mass transfer coefficients from experimental data in a coupled heat and mass transfer manner was finally indicated. Coefficients obtained in this manner can be used in finite difference model to produce more accurate outlet conditions.