Advanced Developments in Solid Desiccant Coated Heat Exchangers and their Potential Applications

To meet the increasing thermal comfort requirements in recent times, applying a solid desiccant coated heat exchanger (SDCHE) air-conditioning system is one of the thrust areas of focus due to its energy efficiency benefits. Fixed stationary bed and rotary wheel desiccant systems are being used widely for dehumidification. In these systems, the increase in the relative humidity of intake process air increases the adsorption heat release from the desiccant, and the desiccant’s temperature increases due to the lower heat transfer efficiency. This effect reduces the COP of these systems since the desiccant adsorption capacity is inversely proportional to the desiccant’s temperature. To overcome the limitations of the fixed stationary beds and rotary wheel desiccant dehumidifiers, SDCHE is a suitable technology for standard vapor-compression air conditioners. These heat exchangers can deliver combined heat and mass transfer between the process air and the working fluid. The process air can be cooled and dehumidified simultaneously by pumping cooling water/refrigerant in the SDCHE. However, SDCHE must be heated cyclically to regenerate the desiccant material. This paper reports a comprehensive review of the literature on the air-to-liquid SDCHE system, its benefits over other conventional dehumidifiers, and various desiccant materials (e.g. Silica gel and Molecular sieves) used in these heat exchangers. Finally, we highlight the potential application of the SDCHE in heat pumps, adsorption chillers, water harvesters, automotive evaporators, and stand-alone air-conditioners.