Determination of air-to-air energy wheels latent effectiveness using humidity step test data

Abstract

Desiccant wheels are capable of recovering a considerable amount of moisture difference between two air streams. This study is aimed at determining the latent effectiveness of a rotary desiccant wheel through small-scale, transient testing. A coating of mesoporous silica gel particles (55μm particle size-pore width 77.5Å) was deposited on an aluminum substrate. The physical properties (particle size, pore width, surface area, and surface functional groups) of the silica gel were characterized and its sorption properties were investigated by nitrogen gas adsorption at 77K. In addition, the equilibrium condition and the kinetics of water vapor sorption on the silica gel sample were studied at 23°C. A test facility was developed to obtain the exchanger transient response during the dehumidification process and the data was used to determine the latent effectiveness of a regenerator constructed with the silica gel coated aluminum. Moreover, the latent effectiveness was determined using a cyclic test with both dehumidification and regeneration cycles. Good agreement was observed between the latent effectiveness values obtained through the single dehumidification and cyclic tests. A correlation from the literature was used to calculate the latent effectiveness of the silica gel coated regenerator. Comparison between the latent effectiveness determined by transient test data and the correlation showed good agreement when Ntum<4.3 and ω>4 rpm.