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Research Papers

Effect of the Capillary Property of Porous Media on the Water Transport Characteristics in a Passive Liquid-Feed DMFC

[+] Author and Article Information
Chao Xu

Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269

Amir Faghri1

Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269faghri@engr.uconn.edu

1

Corresponding author.

J. Fuel Cell Sci. Technol 7(6), 061007 (Aug 20, 2010) (14 pages) doi:10.1115/1.4001761 History: Received June 05, 2009; Revised February 19, 2010; Published August 20, 2010; Online August 20, 2010

The porous diffusion medium (DM) used in fuel cells has a complex heterogeneous structure in which both hydrophilic and hydrophobic pores coexist. The capillary flow in such a mixed-wet DM is mainly controlled by the capillary pressure and saturation relation (CPSR). In order to investigate the water transport characteristics in a passive direct methanol fuel cell (DMFC), taking into account the coexistence of the hydrophilic and hydrophobic pores in the DM, we presented the mechanisms of capillary flow in the mixed-wet DM and provided a comprehensive evaluation of the CPSRs used in various existing fuel cell studies. Then, based on a two-dimensional, two-phase, nonisothermal model for the passive DMFC, we investigated the liquid transport phenomena through the mixed-wet DM by employing an experimentally measured mixed-wet CPSR. Moreover, we compared the water transport predicted by the mixed-wet CPSR and the uniform-wet Leverett CPSR for better understanding of the liquid water transport in passive DMFCs. The results show that water transport in the passive DMFC depends greatly on the CPSR of the DM, which demonstrates an urgent need for the accurate CPSRs of the DM used in fuel cells. It is also shown that the dependence of water transport on the CPSRs can be significantly influenced by the use of a hydrophobic air filter layer at the cathode.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

The curves of two typical capillary pressure versus liquid saturation relations

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Figure 2

Different capillary pressure versus liquid saturation relations used in the fuel cell study: (a) uniform-wet (fully hydrophobic) relations and (b) mixed-wet relations

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Figure 3

(a) Schematic of the passive DMFC and (b) the computational domain

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Figure 4

Scenario of liquid water transport across the cathode DL without a hydrophobic filter layer (a) and with a hydrophobic filter layer (b)

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Figure 5

Distribution of oxygen concentration (mol m−3) across the cathode catalyst layer and diffusion layer at a current density of 130 mA cm−2 for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 6

Distribution of liquid saturation across the cathode catalyst layer and diffusion layer at a current density of 130 mA cm−2 for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 7

Distribution of liquid saturation across the cathode catalyst layer and diffusion layer at the surface of y=0 for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 8

Distribution of liquid pressure across the cathode catalyst layer and diffusion layer at the surface of y=0 for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 9

Polarization and power density curves (a) and variations in the flux of water crossover through the membrane (b) with current density for the passive DMFC using different CPSRs

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Figure 10

Distribution of oxygen concentration (mol m−3) across the cathode catalyst layer and diffusion layer at a current density of 130 mA cm−2 for the passive DMFC with a hydrophobic AFL for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 11

Distribution of liquid saturation across the cathode catalyst layer and diffusion layer at a current density of 130 mA cm−2 for the passive DMFC with a hydrophobic AFL for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 12

Distribution of liquid saturation across the cathode catalyst layer and diffusion layer at the surface of y=0 for the passive DMFC with a hydrophobic AFL for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 13

Distribution of liquid pressure across the cathode catalyst layer and diffusion layer at the surface of y=0 for the passive DMFC with a hydrophobic AFL for different CPSRs: (a) Leverett and (b) mixed-wet

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Figure 14

Polarization and power density curves (a) and variations in the flux of water crossover through the membrane (b) with current density for the passive DMFC with a hydrophobic AFL using different CPSRs

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