A uniform temperature field is desirable in the solid oxide fuel cell stack to avoid local hot regions that contribute to material degradation, thermal stresses, or very high current densities. Various geometric and operational design changes were simulated by numerical modeling of co-flow and counter-flow multi-cell stacks, and the effects on stack maximum temperature, stack temperature difference, and maximum cell temperature difference were characterized. The results showed that 11-17% methane fuel composition for on-cell steam reforming and a reduced reforming rate of 25-50% of the nominal rate was beneficial for a more uniform temperature field. Fuel exhaust recycling up to 30% was shown to provide lower temperature differences for reforming fuel in the co-flow stack, but counter-flow stacks with hydrogen fuel showed higher temperature differences. Cells with large aspect ratios showed a more uniform temperature response due to either the strong influence of the inlet gas temperatures or the greater thermal exchange with the furnace boundary condition. Improved lateral heat spreading with thicker interconnects was demonstrated, but greater improvements towards a uniform thermal field for the same amount of interconnect mass could be achieved using thicker heat spreader plates appropriately distributed along the stack height.
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