Flow Maldistribution and Performance Deteriorations in Membrane-Based Heat and Mass Exchangers

Abstract

Heat mass exchangers are crucial for the prevention of epidemic respiratory diseases such as H1N1 (swine flu). The flow maldistribution affects their performance seriously. The flow maldistribution and the consequent performance deteriorations in heat and mass exchangers are investigated. The focus is on moisture effectiveness deteriorations. As a first step, a computational fluid dynamics (CFD) code is used to calculate the flow distribution, by treating the plate-fin core as a porous medium. Then a coupled heat and moisture transfer model between the two air flows in the plate-fin channels is set up with slug flow assumption in the channels. Using the CFD predicted core face flow distribution data, the sensible heat and moisture exchange effectiveness and the performance deterioration factors are calculated with finite difference scheme. The results indicate that under current core to whole exchanger pressure drop ratio, when the channel pitch is below 2.0 mm, the flow distribution is quite homogeneous and the sensible and latent performance deteriorations due to flow maldistribution can be neglected. However, when the channel pitch is larger than 2 mm, the maldistribution is quite large and a 10–15% thermal deterioration factor and a 20–25% latent deterioration factor could be found. Mass transfer deteriorates much more than heat transfer does due to larger mass transfer resistance through membranes.