Thermal stress analysis of the planar SOFC bonded compliant seal design

Abstract

A new materials joining approach known as the bonded compliant seal (BCS) has recently been developed for hermetically sealing the cell and window frame components in planar solid oxide fuel cell stacks. At the heart of the BCS is a thin deformable metal foil that is designed to decouple the effects of differential thermal expansion between the two components and thereby mitigate the generation of potentially destructive thermal stresses in the stack. While preliminary viability of the BCS design has been demonstrated in small-scale rotationally symmetric test specimens, issues concerning the scale-up of this seal to a size and shape that is prototypic of full-size stacks are addressed here. Finite element analysis was undertaken to investigate the magnitudes of thermally induced stress, strain, and part deflection in the cell, seal, and window frame components under uniform heating and cooling conditions. From the point of stress mitigation, particularly in the brittle ceramic cell, the initial BCS design appears to function quite well by accommodating the mismatch thermal strains as elastic and plastic strain within the sealing foil. However, the model predicts that some bowing will take place within the cell. While the amount of bowing is likely manageable through proper design of the adjacent interconnects, it is believed that a substantial portion of the predicted bow can be eliminated via minor adjustments to the various seal parameters.