Conjugate Mass Transfer in Gas Channels and Diffusion Layers of Fuel Cells

[+] Author and Article Information
S. B. Beale

 National Research Council, Montreal Road, Ottawa, Ontario K1A 0R6 Canadasteven.beale@nrc-cnrc.gc.ca


J. Fuel Cell Sci. Technol 4(1), 1-10 (May 23, 2006) (10 pages) doi:10.1115/1.2393300 History: Received October 18, 2005; Revised May 23, 2006

Prediction of mass transfer effects is a key element in fuel cell design. In this paper, the results of a generalized analysis appropriate to a wide range of designs and flow conditions are presented. Mass transfer in a rectangular gas passage, diffusion layer, and the combination of the two is considered. Fully developed viscous flow is presumed to occur within the passage, while the incompressible form of Darcy’s law is prescribed for the diffusion layer. The mathematical foundations for a simple mass transfer analysis are presented. Detailed calculations are then performed by means of a computational fluid dynamics code. These results are then correlated according to the analytical methodology in terms of nondimensional numbers appropriate to mass transfer analysis; namely, the overall mass transfer driving force as a function of the blowing parameter. Parametric studies are performed for a range of geometries, as characterized by the aspect ratio and blockage factor. It is shown that a simple solution for the overall driving force may readily be obtained from the two individual solutions for the conjugate mass transfer problem. This solution is quite general in its nature, and may readily be used to predict concentration polarization effects for a variety of fuel cells.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Schematic of gas channel and diffusion layer

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Figure 2

Schematic of gas channel

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Figure 3

Values of Sh1* for rectangular ducts as obtained here, compared with data of Schmidt, from Shah and London (12)

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Figure 4

Mass transfer driving force B1 as a function of blowing parameter b1 for gas channel

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Figure 5

Schematic of diffusion layer

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Figure 6

Normalized pressure and velocity fields, α2=18, β=12, b=−1

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Figure 7

Normalized concentration fields, α2=18, β=12

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Figure 8

Sh2* as a function of blockage factor

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Figure 9

B2 vs b2. Diffusion layer β=12.

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Figure 10

Computational grid

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Figure 11

Pressure contours and velocity vectors

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Figure 12

Normalized concentration contours, b2=−1

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Figure 13

B vs b. Conjugate problem, thick diffusion layer, Γeff∕Γ=1.

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Figure 14

B vs b. Conjugate problem, thin diffusion layer, Γeff∕Γ=1.

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Figure 15

B vs b. Conjugate problem, thin diffusion layer, Γeff∕Γ=0.3635.




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