On the importance of air-solution flow rate matching in liquid-desiccant deep-dehumidification system

Abstract

Liquid-desiccant deep-dehumidification (LDDD) systems providing air with a humidity ratio below 5 g/kg have been used in different engineering applications. Matched air and solution flow rates in the dehumidifier/regenerator are crucial for driving force distributing uniformly during the heat and mass transfer between air and desiccant. In this study, the thermal capacity ratios of air to desiccant (m*) is introduced to describe the air-solution flow rate matching degree, and the mismatching characteristics for m* in the LDDD system is revealed and illustrated. Simulations are performed to reveal negative effects of the mismatching characteristics on the heat and mass transfer in the dehumidifier/regenerator. The results demonstrate that the m* values in the dehumidifier and regenerator cannot be simultaneously equal to 1 under the deep dehumidification circumstance. Accordingly, the heat and mass transfer driving forces cannot distribute uniformly in the dehumidifier and regenerator simultaneously, leading to considerable exergy loss. Two strategies are then proposed to make the driving forces distribute uniformly and improve system exergy performance. Under the strategies, the exergy loss during heat and mass transfer in the dehumidifier and regenerator can be reduced by 10.6%–26.8%. Strategy II requires a lower heating source temperature and a lower heating capacity, resulting in a better system performance than Strategy I.