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Research Papers

A Numerical Investigation Into the Interaction Between Current Flow and Fuel Consumption in a Segmented-in-Series Tubular SOFC

[+] Author and Article Information
B. A. Haberman

The Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UKB.Haberman.01@cantab.net

A. J. Marquis

The Department of Mechanical Engineering, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UKa.marquis@imperial.ac.uk

J. Fuel Cell Sci. Technol 6(3), 031002 (May 11, 2009) (8 pages) doi:10.1115/1.3005386 History: Received June 15, 2007; Revised May 06, 2008; Published May 11, 2009

A typical segmented-in-series tubular solid oxide fuel cell (SOFC) consists of flattened ceramic support tubes with rows of electrochemical cells fabricated on their outer surfaces connected in series. It is desirable to design this type of SOFC to operate with a uniform electrolyte current density distribution to make the most efficient use of the available space and possibly to help minimize the onset of cell component degradation. Predicting the electrolyte current density distribution requires an understanding of the many physical and electrochemical processes occurring, and these are simulated using the newly developed SOHAB multiphysics computer code. Of particular interest is the interaction between the current flow within the cells and the consumption of fuel from an adjacent internal gas supply channel. Initial simulations showed that in the absence of fuel consumption, ionic current tends to concentrate near the leading edge of each electrolyte. Further simulations that included fuel consumption showed that the choice of fuel flow direction can have a strong effect on the current flow distribution. The electrolyte current density distribution is biased toward the upstream fuel flow direction because ionic current preferentially flows in regions rich in fuel. Thus the correct choice of fuel flow direction can lead to more uniform electrolyte current density distributions, and hence it is an important design consideration for tubular segmented-in-series SOFCs. Overall, it was found that the choice of fuel flow direction has a negligible effect on the output voltage of the fuel cells.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Gas and ion transport and electrochemical reactions in an SOFC

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Figure 2

A typical segmented-in-series tubular SOFC. The electrochemical cells are printed on both sides of the ceramic tube structure

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Figure 3

Cross-section through the tubular SOFC showing the segmented-in-series fuel cells

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Figure 4

Cross-section through the computational domain (all dimensions in millimeters)

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Figure 5

Vectors of conventional current density plotted in a part of the computational domain centred on cell 2

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Figure 6

A comparison between the current density i distributions predicted by the SOHAB code and an ohmic only model for a mean electrolyte current density of 0.3Acm−2 where fuel flow was neglected. The spatial variation of the potential difference ϕc−ϕa is also shown.

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Figure 7

Hydrogen mole fraction XH2 distribution plotted within the computational domain for a mean electrolyte current density of 0.3Acm−2 where fuel flow was neglected

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Figure 8

Comparison between the normalized current density distributions obtained at different mean electrolyte current densities where fuel flow was neglected

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Figure 9

Hydrogen mole fraction XH2 distribution plotted within the computational domain for a test case where the mean electrolyte current density is 0.3Acm−2 and fuel flow is included (total fraction of fuel consumed f=0.08)

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Figure 10

The effect of the fraction of fuel consumed f on the distribution of the potential difference ϕc−ϕa measured across each electrolyte. In both cases the mean electrolyte current density is 0.3Acm−2

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Figure 11

The effect of the fraction of fuel consumed f on the calculated normalized current density distributions. The same results were obtained for all the six cells simulated.

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Figure 12

Hydrogen mole fraction XH2 distribution plotted within the computational domain for a test case where imean=0.3Acm−2 and the reversed fuel flow was included

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Figure 13

Comparison between the normalized current density distributions obtained at imean=0.3Acm−2 for simulations that included and neglected the fuel flow

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Figure 14

The variation of calculated tube output voltage Etube and ratio of maximum to minimum current density imax∕imin with mean electrolyte current density imean

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