Performance enhancement of rotary desiccant wheel by innovative designs of multiple desiccant layers

Abstract

Rotary Desiccant wheel in the desiccant air conditioning system is used for the dehumidification of process air by adsorption of water vapour by the desiccant (porous media) layer. And while the hot air which is heated up by the heater (or waste heat recovered from other equipments) flows through regeneration side, water is desorbed out from the desiccant and gets regenerated. In a desiccant wheel, the process air enters the wheel at one end with high moisture content and the moisture is continuously transferred from air to desiccant. Since, the equilibrium adsorption capacity of desiccant material is directly proportional to the relative humidity of air in contact, the rate of moisture transfer decreases along the width of the wheel. This is considered to be a bottleneck for the efficiency of a rotary desiccant wheel where improvements can be done. The innovative design of rotary desiccant wheel presented in this paper enhances the moisture removal capacity by using multiple desiccant materials over the width of the wheel and increases the moisture removal capacity and efficiency of the wheel without increasing the overall dimensions of rotary desiccant wheel. The numerical results of this multiple desiccant wheels (Hybrid) are compared with conventional wheel made up of either molecular sieves or Silica gel. The results show that the performance of the wheel can be enhanced by 10–25% by using this innovative design. The governing equations of heat and moisture transfer are discretized using the finite volume method and the simulations are carried out using a code developed in FORTRAN 95.