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Research Papers

Water Management in a Passive DMFC Using Highly Concentrated Methanol Solution

[+] Author and Article Information
Hafez Bahrami

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 8(2), 021011 (Nov 30, 2010) (15 pages) doi:10.1115/1.4002315 History: Received October 27, 2009; Revised June 06, 2010; Published November 30, 2010; Online November 30, 2010

A two-dimensional, steady state, nonisothermal, nonequilibrium, multifluid, two-phase flow model is employed to investigate fuel delivery characteristics, as well as the strong relation between water transport through the membrane and methanol crossover. A porous layer, called the fuel delivery layer, is used between the anode backing layer and the methanol reservoir to be able to employ high concentration methanol solution at the anode reservoir. A simple analytical model for liquid methanol distribution in the anode is presented to show the significant effect of water crossover through the membrane on the methanol dilution at the anode catalyst layer. A comprehensive numerical model is employed to verify the concept developed by the analytical model. The numerical model also accounts for the dissolved water phase in the Nafion membrane. Using a hydrophobic microporous layer at the cathode decreases methanol crossover due to a reduction in water crossover, as well as attaining a water neutral condition. It is found that thickening of the porous fuel delivery layer cannot alleviate the methanol crossover through the membrane without controlling the water transport. The results also show that a cathode microporous layer can significantly reduce the liquid saturation at the cathode backing layer which, in turn, reduces water flooding at the cathode.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of DMFC (a) without WML at the cathode and (b) with a WML

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Figure 2

Analytical result for the effect of an increase in the FDL thickness on the liquid methanol distribution at the anode side for (a) 10M and (b) 15M methanol solutions in the reservoir (I¯=1200 A/m2)

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Figure 3

Liquid methanol distribution at the anode for different FDL thicknesses when (a) 10M and (b) 15M methanol solutions are applied in the reservoir (I¯=1200 A/m2)

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Figure 4

The effect of using a WML at the cathode on the liquid methanol distribution at the anode (a) 10M and (b) 15M(I¯=1200 A/m2)

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Figure 5

The effect of using a cathode WML on the liquid pressure at the cathode side (a) 10M and (b) 15M(I¯=1200 A/m2)

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Figure 6

The effect of utilizing a WML at the cathode on the water content of the membrane when (a) 10M and (b) 15M methanol (I¯=1200 A/m2)

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Figure 7

The effect of using a WML at the cathode on the temperature distribution through all porous layers for (a) 10M and (b) 15M methanol solutions in the reservoir (I¯=1200 A/m2)

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Figure 8

Oxygen distribution at the cathode side for the cases with and without using a WML (a) 10M and (b) 15M(I¯=1200 A/m2)

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Figure 9

Water crossover mechanisms through the membrane versus current density for (a) 10M and (b) 15M methanol solutions fed in the reservoir

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Figure 10

The net water transfer and equilibrium water transfer coefficient when (a) 10M and (b) 15M methanol solutions are fed in the reservoir

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Figure 11

Different mechanisms of methanol crossover through the membrane versus current density for (a) 10M and (b) 15M methanol solutions in the reservoir

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Figure 12

Liquid methanol mass fraction at the interface of the ACL/MEM for two distinct methanol solutions in the reservoir

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