Optimization of a single-cell solid-oxide fuel cell using computational fluid dynamics

William J. Sembler, Sunil Kumar

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Article number021007
JournalJournal of Fuel Cell Science and Technology
Volume8
Issue number2
DOIs
StatePublished - 2011

Fingerprint

Solid oxide fuel cells (SOFC)
Computational fluid dynamics
Channel flow
Electric potential
Air
Parallel flow
Fuel cells
Computer simulation
Current density
Temperature
Electrodes
Acoustic impedance
Air intakes
Electrolytes
Pressure drop
Thermal expansion
Compressors
Dynamic models
Chemical activation
Oxygen

Keywords

  • CFD
  • computational fluid dynamics
  • fuel cell
  • modeling
  • optimization
  • SOFC
  • solid-oxide fuel cell

ASJC Scopus subject areas

  • Mechanical Engineering
  • Mechanics of Materials
  • Renewable Energy, Sustainability and the Environment
  • Electronic, Optical and Magnetic Materials
  • Energy Engineering and Power Technology

Cite this

Optimization of a single-cell solid-oxide fuel cell using computational fluid dynamics. / Sembler, William J.; Kumar, Sunil.

In: Journal of Fuel Cell Science and Technology, Vol. 8, No. 2, 021007, 2011.

Research output: Contribution to journalArticle

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abstract = "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.",
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