An analytical model for heat and mass transfer processes in internally cooled or heated liquid desiccant–air contact units

Internally cooled or heated liquid desiccant–air contact units can be used for effective air dehumidification or desiccant regeneration, respectively. One-dimensional differential equations were utilized in the present study to describe the heat and mass transfer processes with parallel/counterflow configurations. The effects of solution film heat and mass transfer resistances, the variations of solution mass flow rate, non-unity values of Lewis factor and incomplete surface wetting conditions were all considered in the differential model. On considering the relatively narrow ranges of operating conditions in a specified application, the equilibrium humidity ratio of desiccant solution was assumed to be a linear function of its temperature and concentration. Constant approximations of some properties and coefficients were further made to render the coupled equations linear. The differential equations were rearranged and an analytical solution was developed for newly defined parameters. For four possible flow arrangements and three types of commonly used liquid desiccant solutions, results of analytical solutions were compared with those of numerical integrations over a wide range of operating conditions, and the agreement was found to be quite satisfactory. Further, the heat and mass transfer performances were analyzed and some guidance to improve the unit design was provided.