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Research Papers

Water Removal From Hydrophilic Fuel Cell Channels

[+] Author and Article Information
D. A. Caulk

 General Motors Research and Development Center, Warren, MI 48090

J. Fuel Cell Sci. Technol 7(3), 031013 (Mar 12, 2010) (9 pages) doi:10.1115/1.3207876 History: Received September 03, 2008; Revised April 03, 2009; Published March 12, 2010; Online March 12, 2010

This paper describes an approximate method for analyzing two-phase flow of gas and liquid water in fuel cell channels, whose surfaces are sufficiently hydrophilic for liquid water to wick spontaneously into the channel corners. This analysis is used to address the important question of whether the gas flow at typical stoichiometries in such channels is sufficient to remove all the liquid water generated in a proton exchange membrane fuel cell. Since fuel channels are usually much narrower than they are long, it is possible to adopt the usual approximations of lubrication theory and to decompose the general solution for the liquid motion into two parts: (1) that driven by the channel pressure gradient and (2) that driven by surface shear stress from the faster moving gas. When both parts of the solution are combined with the mass balance equations, it is possible to derive a pair of partial differential equations for the water depth and gas flow rate that depend on distance down the channel and time. Steady solutions of these equations are explored to determine the amount of liquid water that accumulates in the channel over a broad range of fuel cell operating conditions.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Cross section of flow channel showing water films in the two corners opposite the gas diffusion layer

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Figure 2

Average gas velocity, normalized by the results for a dry channel, for various aspect ratios and different water depths in the channel corners, assuming the water is rigid

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Figure 3

Finite element calculations of the nondimensional shear stress fT at the center of the water film, compared with the function defined by Eq. 38 for various aspect ratios and different water depths in the channel corners

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Figure 4

Flow resistance functions FP and FT for various values of the corner half-angle α and the contact angle θ. Symbols represent individual finite element solutions.

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Figure 5

Solution of the mass balance Eq. 54 for the cross-sectional area of liquid water in 1 mm square channels, 200 mm long, and spaced 1 mm apart, using the properties and operating conditions in Table 1. Heavy lines correspond to solutions with surface tension, and light lines correspond to solutions without surface tension.

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Figure 6

Ratio of pressure to gas shear forces on the liquid film, from Eq. 61, as a function of water depth

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Figure 7

Effect of contact angle (in degrees) on steady water accumulation in anode and cathode flow channels

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Figure 8

Effect of channel corner angle 2α (in degrees) on steady water accumulation in anode and cathode flow channels

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Figure 9

Effect of aspect ratio on steady water accumulation in anode and cathode flow channels

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Figure 10

Effect of pressure on steady water accumulation in anode and cathode flow channels

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Figure 11

Effect of temperature (in °C) on steady water accumulation in anode and cathode flow channels

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Figure 12

Effect of stoichiometry on steady water accumulation in anode and cathode flow channels

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Figure 13

Effect of current density (in A/cm2) on steady water accumulation in anode flow channels

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