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Research Papers

Dynamic Model for Understanding Spatial Temperature and Species Distributions in Internal-Reforming Solid Oxide Fuel Cells

[+] Author and Article Information
Brendan Shaffer

National Fuel Cell Research Center,  University of California, Irvine, CA, 92697–3550

Jacob Brouwer1

National Fuel Cell Research Center,  University of California, Irvine, CA, 92697–3550jb@nfcrc.uci.edu

1

Corresponding author.

J. Fuel Cell Sci. Technol 9(4), 041012 (Jun 19, 2012) (11 pages) doi:10.1115/1.4006477 History: Received January 30, 2012; Revised February 17, 2012; Published June 19, 2012; Online June 19, 2012

Direct internal reformation of methane in solid oxide fuel cells (SOFCs) leads to two major performance and longevity challenges: thermal stresses in the cell due to large temperature gradients and coke formation on the anode. A simplified quasi-two-dimensional direct internal reformation SOFC (DIR-SOFC) dynamic model was developed for investigation of the effects of various parameters and assumptions on the temperature gradients across the cell. The model consists of 64 nodes, each containing four control volumes: the positive electrode, electrolyte, negative electrode (PEN), interconnect, anode gas, and cathode gas. Within each node the corresponding conservation and chemical and electrochemical reaction rate equations are solved. The model simulates the counter-flow configuration since previous research (Achenbach, 1994, “Three-Dimensional and Time-Dependent Simulation of a Planar Solid Oxide Fuel Cell Stack,” J. Power Sources, 49 (1), p. 333) has shown this configuration to yield the smallest temperature differentials for DIR-SOFCs. Steady state simulations revealed several results where the temperature difference across the cell was considerably affected by operating conditions and cell design parameters. Increasing the performance of the cell through modifications to the electrochemical model to simulate modern cell performance produced significant changes in the cell temperature differential. Improved cell performance led to a maximum increase in the temperature differential across the cell of 31 K. An increase in the interconnect thickness from 3.5 to 4.5 mm was shown to reduce the PEN temperature difference about 50 K. Variation of other physical parameters such as the thermal conductivity of the interconnect and the rib width also showed significant effects on the temperature distribution. The sensitivity of temperature distribution to heat losses was also studied, showing a considerable effect near the fuel and air inlets. Increased heat transfer from the cell edges resulted in severe temperature gradients approaching 160 K/cm. The dynamic capability of the spatially resolved dynamic model was also demonstrated for a 45% power increase perturbation while maintaining constant fuel and air utilizations.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

SECA improvements (taken from Ref. [1])

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Figure 4

No pre-reforming, PEN temperature and current density distributions

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Figure 5

No pre-reforming, concentration distributions for (a) high and (b) low performance cells

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Figure 7

Partial pre-reformation, PEN temperature and current density distributions

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Figure 8

Partial pre-reforming, concentration distributions for (a) high and (b) low performance cells

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Figure 9

Partial pre-reformation, Nernst potential and polarization distributions

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Figure 11

Sensitivity of maximum cell temperature difference (DTPEN) to interconnect thickness

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Figure 16

Response of minimum, maximum, and average PEN temperatures to the 45% power increase

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Figure 17

Response of current density distribution to the 45% power increase

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Figure 18

Response of PEN temperature distribution to the 45% power increase for 4000 s after the dynamic

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Figure 19

Response of hydrogen concentration distribution to the 45% power increase

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Figure 20

Response of methane concentration distribution to the 45% power increase

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Figure 1

Schematic of the solid oxide fuel cell model

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Figure 2

Fuel Cell Dimensions

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Figure 6

No pre-reforming, Nernst potential and polarization distributions

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Figure 12

Sensitivity of maximum cell temperature difference (DTPEN) to rib width

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Figure 13

Effect of edge heat loss with ambient temperature of 950 K on the PEN temperature and current density distributions

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Figure 10

Sensitivity of maximum cell temperature difference (DTPEN) to interconnect thermal conductivity

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Figure 14

Current density, power density, and cell voltage during power increase

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Figure 15

Response of anode and cathode gas exit temperatures to the 45% power increase

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