Modeling and parametric analysis of silica-gel desiccant wheels

A number of mathematical models has been developed to predict the heat and mass transfer behavior of moisture transport in air dehumidification applications, with rotary desiccant wheels. A complete model would account for the following mechanisms of transport.1. convective transport of heat and moisture between the air and the desiccant surface (gas side resistances)2. diffusion of moisture and conduction of heat through the solid desiccant layer (solid side resistances)The differential equations, that represent these transport mechanisms, will generally be set up to describe a single desiccant coated flow channel, traversing through the respective supply and regeneration air streams in a 360 degree circular path. Symmetry would suggest that the differential equations be solved in two directions (axial and radial). However, many authors have found that a simple one dimensional (axial) model with gas side resistances only, adequately predicts the experimental performance of air dehumidification in rotary desiccant wheels. In this paper, a heat and mass transfer model is presented incorporating gas side resistances. The model shows reasonable agreement with experimental data. The model is used to conduct a parametric analysis to determine the optimum rotation speed of the wheel at various regeneration temperatures.