Simulation of thermal stresses in anode-supported solid oxide fuel cell stacks
Structural stability issues in planar solid oxide fuel cells (SOFC) arise from the mismatch between the coefficients of thermal expansion (CTE) of the components. The stress state at operating temperature is the superposition of several contributions, which differ depending on the component. First, the cells undergo residual stresses due to the sintering phase during the manufacturing process. Furthermore, the load applied during the assembly of the stack to ensure the electric contact and flatten the cells prevents a completely stress-free expansion of each component during the heat-up. Finally, thermal gradients cause additional stresses in operation. The temperature profile generated by a thermo-electro-chemical model implemented in an equation oriented process modeling tool (gPROMS) was imported into finite-element software (ABAQUS) to calculate the stress distribution in all components of a representative SOFC repeat element. The different layers of the cell, i.e. anode, electrolyte, cathode, compensating layer and compatibility layer, were considered in the analysis by using the submodelling capabilities of the finite-element tool. The assessment of the risks of failure was performed by the Weibull analysis. The occurrence of plastic deformation and the dependence on temperature of both CTE and Young’s modulus of the metallic parts were implemented in the finite-element model. Both steady-state and dynamic simulations were performed, with an emphasis on the cycling of the electrical load: even though an uncoupled approach was used, the loss of contact computed by the finite-element tool was considered in the thermo-electro-chemical. The study was carried out in an incremental manner. The residual stresses were dominating the stress state in the cell, except in severe operation conditions. Thus the cell at room temperature after the reduction procedure was revealed as the most critical case. On the contrary, thermal gradients induced irreversible deformation of the metallic components in the area submitted to the highest temperature.
Record created on 2011-03-01, modified on 2016-08-09