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Research Papers

Optimization of a Single-Cell Solid-Oxide Fuel Cell Using Computational Fluid Dynamics

[+] Author and Article Information
William J. Sembler

 United States Merchant Marine Academy, 300 Steamboat Road, Kings Point, NY 11024semblerw@usmma.edu

Sunil Kumar

 Polytechnic Institute of New York University, 6 MetroTech Center, Brooklyn, NY 11201skumar@poly.edu

J. Fuel Cell Sci. Technol 8(2), 021007 (Nov 29, 2010) (12 pages) doi:10.1115/1.4002616 History: Received July 14, 2010; Revised August 28, 2010; Published November 29, 2010; Online November 29, 2010

To determine the effects of various parameters on the performance of a solid-oxide fuel cell (SOFC), a series of simulations was performed using computational fluid dynamics (CFD). The first step in this process was to create a three-dimensional CFD model of a specific single-cell SOFC for which experimental performance data had been published. The CFD simulation results developed using this baseline model were validated by comparing them to the experimental data. Numerous CFD simulations were then performed with various thermal conditions at the cell’s boundaries and with different fuel and air inlet temperatures. Simulations were also conducted with fuel utilization factors from 30% to 90% and air ratios from 2 to 6. As predicted by theory, conditions that resulted in higher cell temperatures or in lower air and fuel concentrations resulted in lower thermodynamically reversible voltages. However, the higher temperatures also reduced Ohmic losses and, when operating with low to moderate current densities, activation losses, which often caused the voltages actually being produced by the cell to increase. Additional simulations were performed during which air and fuel supply pressures were varied from 1 atm to 15 atm. Although the increased pressure resulted in higher cell voltages, this benefit was significantly reduced or eliminated when air- and fuel-compressor electrical loads were included. CFD simulations were also performed with counterflow, crossflow, and parallel-flow fuel-channel to air-channel configurations and with various flow-channel dimensions. The counterflow arrangement produced cell voltages that were equal to or slightly higher than the other configurations, and it resulted in a differential temperature across the electrolyte that was significantly less than that of the parallel-flow cell and was close to the maximum value in the crossflow cell, which limits stress caused by uneven thermal expansion. The use of wider ribs separating adjacent flow channels reduced the resistance to the electrical current conducted through the ribs. However, it also reduced the area over which incoming fuel and oxygen were in contact with the electrode surfaces and, consequently, impeded diffusion through the electrodes. Reducing flow-channel height reduced electrical resistance but increased the pressure drop within the channels. Plots of voltage versus current density, together with temperature and species distributions, were developed for the various simulations. Using these data, the effect of each change was determined and an optimum cell configuration was established. This process could be used by fuel cell designers to better predict the effect of various changes on fuel cell performance, thereby facilitating the design of more efficient cells.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Planar solid-oxide fuel cell

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Figure 2

SOFC CFD model validation cell voltages

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Figure 3

SOFC and Nernst voltages versus thermal boundary condition

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Figure 4

SOFC average electrolyte temperatures versus thermal boundary conditions

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Figure 5

SOFC activation overvoltage versus thermal boundary conditions

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Figure 6

SOFC voltage versus fuel and air inlet temperature

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Figure 7

SOFC exhaust and average electrolyte temperatures versus fuel and air inlet temperature

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Figure 8

SOFC with air and fuel heaters

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Figure 9

Fuel and air heater outlet temperatures with SOFC inlet=1123 K

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Figure 10

Fuel and air heater outlet temperatures with SOFC inlet=750 K

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Figure 11

SOFC and Nernst voltages versus fuel utilization

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Figure 12

SOFC average electrolyte temperature versus fuel utilization

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Figure 13

Hydrogen distribution at anode-electrolyte interface versus fuel utilization

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Figure 14

Electrolyte temperature distribution versus fuel utilization

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Figure 15

SOFC and Nernst voltages versus air ratio

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Figure 16

SOFC average electrolyte temperature versus air ratio

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Figure 17

Oxygen distribution at cathode-electrolyte interface versus air ratio

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Figure 18

Electrolyte temperature distribution versus air ratio

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Figure 19

SOFC (Vc) and Nernst (VN) voltages versus air and fuel flow rates

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Figure 20

SOFC average electrolyte temperature versus air and fuel flow rates

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Figure 21

SOFC cathode-flow-channel pressure drop versus air flow

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Figure 22

SOFC anode-flow-channel pressure drop versus fuel flow

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Figure 23

SOFC and Nernst voltages versus operating pressure

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Figure 24

SOFC and Nernst voltages with operating pressures=1 atm and 15 atm

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Figure 25

SOFC average electrolyte temperature with operating pressure=1 atm and 15 atm

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Figure 26

Power versus operating pressure

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Figure 27

SOFC cell (Vc) and Nernst (VN) voltages versus flow orientation

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Figure 28

SOFC average electrolyte temperature versus flow orientation

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Figure 29

SOFC electrolyte temperature distribution versus flow orientation (current density=1400 mA/cm2)

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Figure 30

SOFC flow-channel arrangement

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Figure 31

SOFC flow-channel/rib width detail (1 mm channel height)

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Figure 32

SOFC cell voltage versus flow-channel/rib width

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Figure 33

Effect of channel/rib width on O2 diffusion through cathode (current density=680 mA/cm2)

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Figure 34

Effect of channel/rib width on H2 diffusion through anode (current density=680 mA/cm2)

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Figure 35

SOFC cell flow-channel height detail (1.5 mm channel and 0.5 mm rib widths)

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Figure 36

SOFC cell voltage versus flow-channel height

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Figure 37

SOFC cathode-flow-channel pressure drop versus channel height

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Figure 38

SOFC anode-flow-channel pressure drop versus channel height

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Figure 39

Final SOFC single-cell configuration

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