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Research Papers

Elucidating Liquid Water Distribution and Removal in an Operating Proton Exchange Membrane Fuel Cell via Neutron Radiography

[+] Author and Article Information
Michael A. Hickner1

Department of Fuels and Energy Transitions, Sandia National Laboratories, Albuquerque, NM 87185

Ken S. Chen2

Department of Nanoscale and Reactive Processes, Sandia National Laboratories, Albuquerque, NM 87185-0836kschen@sandia.gov

Nathan P. Siegel

Department of Solar Technologies, Sandia National Laboratories, Albuquerque, NM 87185

1

Present address: Materials Science and Engineering Department, The Pennsylvania State University, University Park, PA 16802.

2

Corresponding author.

J. Fuel Cell Sci. Technol 7(1), 011001 (Oct 05, 2009) (5 pages) doi:10.1115/1.3115624 History: Received June 17, 2007; Revised December 01, 2007; Published October 05, 2009

Neutron radiography was used to quantify the steady-state water content and its distribution in a 50cm2 operating proton exchange membrane fuel cell. It was observed that the liquid water distribution near the corners of the gas-flow channels (GFCs) is influenced by the local gas-flow velocity as determined by the cathode stoichiometric flow ratio. At low velocity, the distribution of liquid water down the channel was found to be fairly uniform with only a slight reduction in liquid water content at the exit of the GFC corners. It was further observed that as the cathode gas-flow velocity is increased, a noticeable pattern develops in which liquid water is concentrated at the entrance to the GFC corners and becomes depleted in the corner and near the exit of the corner; liquid water content again increases further down the channel away from the corners. A single-phase computational fluid dynamics (CFD) model was developed and employed to help explain the observed water-distribution patterns. Flow-fields computed from our CFD model reveal recirculation regions in the GFC corners as well as in the areas of increased local gas-flow velocity, which help explain the experimentally observed liquid water distribution.

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Figures

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Figure 2

Water content as a function of time (with markers at the mean and two standard deviations from the mean), the averaged image, and snapshots of the cell as a function of time for pseudo-steady-state operation at 60°C and 1 A/cm2 with two stoic cathode flow in a 50 cm2 active area PEM fuel cell

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Figure 3

Liquid water content and images of liquid water slugs at 1 A/cm2 and 60°C for three flow channel velocities: (a) two stoics, vavg=8.4 m/s, 15 mg/cm2H2O; (b) four stoics, vavg=15.9 m/s, 14 mg/cm2H2O; and (c) six stoics, vavg=22.3 m/s, 13 mg/cm2H2O

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Figure 4

Full cell and close-up view of flow channels for the four stoic 1 A/cm2 case at 60°C showing water accumulation at the entrance to the channel bends and a relatively water-free region after the bend

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Figure 5

(a) CFD simulation output showing the predicted velocity distribution through a corner of the GFC, (b) a neutron radiograph of the same region showing the liquid water distribution, and (c) diagram of the corner regions depicting Zones 1–3

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Figure 6

Predicted velocity distribution through a corner of the flow-field for both the high flow rate (SR=4, vinlet=15.9 m/s) and low flow rate (SR=2, vinlet=8.4 m/s) cases

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Figure 7

(a) A vector plot of the calculated velocity distribution in the corner of the flow-field showing recirculation regions and (b) neutron imaging results of the same region showing an increase in water content. SR=4.0

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Figure 1

A drawing of the 50 cm2 flow-field used in the CFD simulations

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