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Research Papers: Heat and Mass Transfer

Thermal and Start-Up Characteristics of a Miniature Passive Liquid Feed DMFC System, Including Continuous/Discontinuous Phase Limitations

[+] Author and Article Information
Jeremy Rice

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

Amir Faghri1

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

1

Corresponding author.

J. Heat Transfer 130(6), 062001 (Apr 22, 2008) (11 pages) doi:10.1115/1.2891156 History: Received December 19, 2006; Revised August 07, 2007; Published April 22, 2008

The thermal and start-up characteristics of a passive direct methanol fuel cell system are simulated using a numerical model. The model captures both the thermal characteristics of the fuel cell and the passive fuel delivery system using a multifluid model approach. Since the fuel cell is run without any active temperature control, the temperature may rise until the convective and evaporative cooling effects balance the heat produced in the chemical reactions. The cell temperature can vary as much as 20°C, and it is vital to model the thermal effects for accurate results. The numerical model also includes continuous and discontinuous phase limitations, as well as a probabilistic spread of the porous properties. These added physical characteristics qualitatively portray the departure of carbon dioxide from the anode side of the fuel cell.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the setup for DMFC polarization tests

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Figure 2

Schematic of the DMFC fuel delivery system

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Figure 3

Schematic of a porous zone with (a) one continuous phase and one discontinuous phase and (b) two continuous phases

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Figure 4

Probability distribution function f for the porous properties

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Figure 5

Continuous phase flow paths of CO2 with (a) constant pore properties and (b) distributed pore properties compared to the (c) distribution of CO2 bubbles generated experimentally at the anode gas diffusion layer

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Figure 6

Contour plots of CO2 in the anode gas diffusion layer for (a) constant pore properties and (b) distributed pore properties

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Figure 7

Comparison of cell polarization and power density of numerical (lines, solid Tref=293K, dashed Tref=300K) and experimental results from Guo and Faghri (7) (symbols) for (a) 1M, (b) 2M, and (c) 3M methanol solutions

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Figure 8

Cell temperature rise, ΔT=Tcathode−Tref, versus current density for different methanol concentrations; experimental results from Guo and Faghri (7)

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Figure 9

Effect of relative humidity on cell polarization and temperature rise at ambient conditions of (a) 293K and (b) 300K

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Figure 10

Methanol crossover reaction, and methanol and water evaporation rates normalized by the stoichiometric coefficient and the sum of the cell current density and the crossover current for 2M methanol feed concentration with ambient temperatures of (a) 293K and (b) 300K

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Figure 11

Cell start-up with varying cell voltage and a water storage layer thickness and porosity of 1.2mm and 0.9, respectively, a methanol distribution porosity of 0.3, and an effective air-breathing thickness of 5mm at an ambient temperature of 293K

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Figure 12

Cell start-up with varying effective air-breathing lengths and a water storage layer thickness and porosity of 1.2mm and 0.9, respectively, a methanol distribution porosity of 0.3, a cell voltage of 0.25V, and an ambient temperature of 293K

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Figure 13

Cell start-up temperature rise and water consumption ratio with a varying air-breathing effective length

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Figure 14

Cell start-up methanol consumption ratio of the methanol used to produce useful work, and methanol evaporated

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