Study of a waste heat driven modified packed desiccant bed dehumidifier

A modified version of the cross cooled desiccant bed is presented. The parallel flow channels are subdivided longitudinally and packed with silica gel particles instead of being glued to the side walls. The bed is regenerated utilizing the rejected heat from a LiBrH2O absorption cooling machine and both are integrated in a solar powered air conditioning system. Two beds are alternately working in the humidification/dehumidification cycle. Treating the matrix and the desiccant separately, a five governing equation model, describing the heat and mass transfer between the passing air flow, the desiccant material and the matrix metallic structure, is introduced and given. This is numerically solved for both the humidification mode and the dehumidification mode with each occupying half of the bed cyclic duration. For a case study in Jeddah, with a cyclic duration of 15 minutes, the results showed an overall coefficient of performance of 1.2 which is 53% higher than that for the absorption machine alone. Moreover, adding the desiccant bed to the air conditioning system raised the evaporator temperature to 19.3°C compared with the 11.5°C required for the absorption machine alone.