| dc.description.abstract | Solid oxide fuel cells (SOFCs) utilize ceramics as the anode, electrolyte, and cathode (often called a positive electrode-electrolyte-negative electrode, PEN) and operate at high temperatures such that they have the highest efficiencies of all fuel cells. The high-temperature operation, however, gives rise to significant thermal stresses caused from the mismatch of coefficient of thermal expansion (CTE) and temperature gradients in the SOFC system. Therefore, a comprehensive thermal stress analysis of SOFC stack is necessary for the success in design and operation of a SOFC system. The aim of this study is, by using finite element simulation, to characterize the thermal stress distribution in a planar SOFC stack during transients and steady operation.
An integrated electrochemical and thermal analysis was first conducted to generate the temperature profiles in a 3-cell SOFC stack during various start-up and steady stages. The obtained temperature fields within the cell stack were subsequently applied to a thermal stress analysis using a 3-D finite element model of a 3-cell stack. Each unit cell consists basically of a PEN assembly, interconnect, nickel mesh, and gas-tight glass-ceramic seals. Incorporation of the glass-ceramic sealant, which was never considered in other previous studies, into the 3-cell FEA model would produce more realistic results in thermal stress analysis. In particular, the effect of viscous behavior of glass-ceramic sealant on thermal stress distribution within the cell stack was investigated. In addition, the effects of stack support condition, temperature gradient, cyclic operation were also characterized. Modeling results indicated that a change in the support condition at the bottom frame of the 3-cell stack would not cause significant changes in the thermal stress distribution. Thermal stress distribution did not differ significantly in each unit cell within the 3-cell stack due to a negligible out-of-plane thermal stress gradient. By considering the viscous characteristics of glass-ceramic sealant at temperatures above the glass-transition temperature (Tg), relaxation of thermal stresses in PEN and glass-ceramic sealant was predicted. Effect of operating cycles on the variation of thermal stress was also simulated and the results indicated that a significant increase in thermal stress in PEN and glass-ceramic sealant would be expected with increasing cycle number. | en_US |