Performance Deteriorations from Flow Maldistribution in Air-to-Air Heat Exchangers: A Parallel-Plates Membrane Core Case

Abstract

Parallel-plates membrane cores have been widely used in air-to-air heat exchangers for fresh air heat and moisture recovery, which are also called total heat exchangers. Flow maldistribution and the consequent performance deteriorations are of great interest. The flow maldistribution is predicted with a CFD code, by treating the parallel-plates core as a two-dimensional porous media. Then, a coupled heat and moisture transfer model between the two air flows in the parallel-plates channels is set up. Using the CFD predicted flow distribution data on core face, the sensible heat and moisture exchange effectiveness and the performance deterioration factors are calculated with finite-difference scheme. Experiments are performed to validate the heat mass transfer model. The results indicate that for the current structure, 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 are below 9% and can be neglected. However, when the channel pitch is larger than 2 mm, the maldistribution is quite large and the consequent thermal and latent performance can be deteriorated by 28%. The flow maldistribution the consequent thermal and latent effectiveness deteriorations for parallel-plates cores are more serious than those for plate-fin cores previously reported.