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Research Papers: Heat Exchangers

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

[+] Author and Article Information
Li-Zhi Zhang1

Key Laboratory of Enhanced Heat Transfer and Energy Conservation of Education Ministry, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, Chinalzzhang@scut.edu.cn

1

Corresponding author.

J. Heat Transfer 131(11), 111801 (Aug 26, 2009) (7 pages) doi:10.1115/1.3154832 History: Received December 23, 2008; Revised April 28, 2009; Published August 26, 2009

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.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 9

Performance deterioration factors for the three cores under various air flow rates

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Figure 1

Schematic of a cross-flow enthalpy exchanger with a membrane core

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Figure 2

Experimental setup of the enthalpy exchanger with a membrane core

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Figure 3

The calculating domain for fresh air flow

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Figure 4

Sensible effectiveness of the three plate-fin cores under various air flow rates. The solid line is the calculated values, and the discrete dots are the measured data.

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Figure 5

Latent effectiveness of the three plate-fin cores under various air flow rates. The solid line is the calculated values, and the discrete dots are the measured data.

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Figure 6

Velocity nonuniformity on the core face, Core B with a channel pitch of 2.5 mm

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Figure 7

Local dimensionless humidity of fresh air on the core outlet face (x∗=1), Core A with channel pitch of 4 mm

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Figure 8

Local dimensionless humidity of fresh air on the core outlet face (x∗=1), Core C with channel pitch of 1.8 mm

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