Flow maldistribution and performance deteriorations in a counter flow hollow fiber membrane module for air humidification/dehumidification

Performance deterioration caused by flow maldistribution in a counter flow hollow fiber membrane module used for air humidification or dehumidification is investigated. To obtain the real flow fields, a CFD code is used to calculate the flow distribution in the whole membrane module, by treating the fiber bundle as a porous media. Then the module is equivalently transformed into a series of mini double-pipe heat and mass exchangers. Coupled heat and moisture transfer between the air flow and the water flow are studied with this mini double pipe model. The sensible cooling and humidification efficiencies are calculated with the maldistribution of velocities in the bundle. The results indicate that the packing fraction affects the flow maldistribution substantially. The consequent sensible cooling and humidification efficiencies deteriorate significantly. Depending on air flow rates, the sensible cooling efficiencies can be deteriorated by 17-36%, and the humidification efficiencies can be deteriorated by 21-39%.