Wettability analysis of desiccant beads for HVAC systems

Vapour adsorption plays a fundamental role in the operation and performance of innovative heat and mass transfer devices for latent heat recovery in HVAC systems. Materials to be used for such devices should present a high affinity with water vapour; at the same time pores should not be flooded in case the surface finds itself in contact with liquid water (e.g., due to moisture formation) and the surface should minimize the wetted parts. From the latter point of view hydrophobic microporous surfaces would be the most suitable; on the contrary, commonly used materials have hydrophilic and/or macroporous surfaces and their behaviour in presence of moisture is still not fully understood. Therefore, this paper is aimed at studying (mostly experimentally, with the support of numerical simulations) wettability and interaction with water, together with adsorption isotherms, of three commercially available desiccant beads (Silica Gel, Silica Gel impregnated with LiCl, Activated Alumina) Results evidence that the behaviour is significantly different between the three materials, even if their static and dynamic wettability is quite similar.