Modelling and simulation of water vapor adsorption in silica gel bidisperse beds

Desiccant cooling systems are widely recognized as an alternative technology to vapor compression cooling. Desiccant systems are attractive for air conditioning applications due to the possible use of low-grade heat and green refrigerants in their operation. In such systems, air dehumidification is achieved using bed compacted with desiccant materials such as silica gel, activated alumina, and zeolite. Desiccant systems, on the other hand, present a low coefficient of performance due to the poor heat and mass transfer in the adsorbent bed. A way to enhance the heat and mass transfer in desiccant systems can be accomplished by optimizing the adsorbent packing in the bed. This paper presents a numerical investigation of the dynamics of water vapor adsorption in silica gel bidisperse bed. The adsorbent bed is compacted with particles of two different sizes to reduce the voids between the adsorbent particles and hence increase the amount of desiccant and the adsorbed water mass in the bed. The effect of bidisperse packing in the air dehumidification capacity and adsorbed water mass is studied. The influence of the pressure drop applied on the adsorbent column and the inlet air conditions in the dehumidification process is also investigated. The numerical results showed that bidisperse packing increases the dehumidification capacity (improvement of 22.9%) and the amount of water adsorbed (improvement of 25%) in the bed compared to the case where monodisperse packing is applied to the system, contributing to the improvement in the performance of desiccant beds in air conditioning applications.