Solid- and gas-side resistances of a silica-gel desiccant wheel

The operation of a solid desiccant evaporative cooling system largely depends on the dehumidification ability of the desiccant wheel and mathematical models are an effective tool to predict the transport behaviour of this wheel. A complete theoretical model would account for both the gas-side resistance, which is due to the convective heat and mass transfer between the air and the desiccant surface, and the solid-side resistance, which is caused by the diffusion of moisture and conduction of heat through the solid desiccant layer. A mathematical model is developed by deriving the partial differential equations of mass and energy balance of a representative channel the desiccant wheel moving through the supply and regeneration air streams in a 360° circular path. The effect of these resistances at different operating conditions on the performance of the wheel is rarely investigated. In this paper, two heat and mass transfer models are presented, the first one incorporating gas-side resistance and the second one includes both solid-side and gas-side resistances. The models are compared with experimental data. It can be concluded that the gas-side resistance is of considerably higher significance compared to the solid-side resistances