Transient performance of coupled heat and mass transfer in cross-flow hollow fiber membrane module for air dehumidification

Abstract

Membrane-based liquid desiccant dehumidification has great advantages over traditional method, particularly in avoiding liquid droplets moving into the process air. This paper proposes a simple model to predict the transient performance of the hollow fiber membrane-based dehumidification module. To simplify the fiber-to-fiber influence, the modeled membrane module is assumed to be a parallel-plates heat mass exchanger. The model has been calibrated and validated with a transient experiment reasonably well. Impacts of various parameters on the transient performance were studied by using the proposed model. The results show that the variation of air temperature is more significant than air humidity. The absorption heat of water vapor is the main resistance of heat and mass transfer. It initially restricts the growth of the cooling effectiveness, and then limits the driving potential for moisture transfer. Therefore, it brings the dehumidification effectiveness down. It is found that reducing the heat capacity rate ratio can reduce the equilibrium time, and increase the cooling and dehumidification effectiveness. The high packing density increases the dehumidification effectiveness with a negligible effect of somewhat drop in cooling effectiveness. By contrast, the geometry of the fiber packing arrangement has little influence on dynamic performance of the module formed by numerous fibers. The membrane module can fit the change of weather conditions by varying solution temperature on the inlet of the dehumidifier with the help of this dynamic model. The cooling and dehumidification effectiveness also increase to improve heat and mass transfer performance of the dehumidifier under the adjustment.