Mathematical Modeling of Heat and Mass Transfer in Regenerators with Desiccant Materials

Abstract

The main component of a solid-desiccant based cooling cycle is the desiccant dehumidifier, which in most cases is found in the form of an active desiccant wheel. Another component that can be frequently found in desiccant cooling systems is an enthalpy wheel, also called an energy wheel or a passive desiccant wheel. Both devices are regenerative exchangers that work based on the same principle: they employ hygroscopic sorbent materials in their matrices, allowing that both heat and water be exchanged. The main difference between these regenerative exchangers is that active desiccant wheels are aimed at dehumidification, and therefore employ a greater amount of sorbent material, whereas enthalpy wheels are aimed at energy exchange and hence require less sorbent quantities. In spite of the differences in applications and construction, the mathematical modeling of heat and mass transfer that occur within active desiccant wheels and enthalpy wheels can be done in a unified fashion. In this context, the main purpose of this chapter is to present different types of formulation that can be used to describe the transport processes that occur in these regenerative exchangers. Since most variation in mathematical models among literature studies are seen in the transport equations for the adsorbent layer that encompass the porous desiccant material, the discussion herein presented will be mainly focused on modeling heat and mass transfer within desiccant materials.