Dehumidification performance of mass exchangers consisting of silica aerogel coated metal foams

Separate sensible and latent cooling systems offer significant increases in the overall performance of cooling/dehumidification systems compared to conventional vapor-compression air-conditioning systems. Key to the energy efficiency of such systems is the performance of the heat and mass exchangers, which provide sensible cooling and dehumidification. Solid-desiccant-coated enthalpy wheels have been in use to control the moisture content of supply air for several decades. However, they have several disadvantages, including inefficient process control, relatively large volume and operational cost. In the current study, the performance of an aerogel-coated, metal-foam mass exchanger has been evaluated and compared to an enthalpy wheel for managing the latent load. Transient and steady state performance models have been developed based on the thermal-hydraulic performance of metal foams (j and f factors)1, mass diffusion coefficients (D) and adsorption/desorption isotherms. The objective of this study is to determine the feasibility of such system to replace conventional enthalpy wheels. The effect of geometry and base material of metal foam, type of silica aerogel and thickness of coating has been analyzed to determine the impact of such parameters on the overall performance of proposed dehumidification device. The study concludes that a significant amount of energy can be saved when the proposed dehumidification system is used in place of a conventional enthalpy wheel to control the moisture content of the supply stream in air conditioning systems.