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. In operation, finally, thermal gradients cause additional stresses. 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. An uncoupled approach was used, since no direct feedback from the stress calculation to the thermo-electro-chemical model exists. The thermal stresses in the components of the repeat element were simulated in both steady-state and dynamic operations. Particular conditions such as current load shutdown, and cooling to room temperature after operation, were investigated as well. 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. Assessment of the risks of failure was performed by the widely used Weibull analysis. The occurrence of plastic deformation and the dependence on temperature of both CTE and Young’s modulus of the metallic parts as well as the orthotropic nature of the compressive sealant were implemented in the finite-element model. 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 interconnector in the area submitted to the highest temperature.
Record created on 2011-03-01, modified on 2016-08-09