Abstract
Due to the elevated operating temperatures (800–1000 °C) of tubular solid oxide fuel cells (SOFC), severe thermal stresses are produced during their operation. Functionally graded materials (FGMs) are used in anodes and cathodes to reduce the specific thermal stresses. The use of FGMs compensates for the effect of any sudden shift in the coefficient of thermal expansion of these electrodes with respect to the electrolyte. In this study, the tubular SOFC efficiency, performance, and produced thermal stresses were numerically investigated. A 3D numerical model that includes the equations of mass conservation, momentum, charging transport, and electricity was developed. These coupled equations of the electrochemical phenomena were solved using ANSYS 19.1-Fluent Solver. The temperature values that were obtained were sequentially introduced into the structural finite element model as body loads, and the model was solved with ANSYS 19.1-MAPDL Solver. The numerical model was validated against previously published experimental results. For both electrodes, the FGM was identified by a grading index “m.” The use of the FGM for the anode and cathode instead of conventional electrodes increased the tubular SOFC efficiency and reduced the thermal stress. Optimum results were obtained at grading index m = 2.0, with the cell output increased by 8 % and induced thermal stresses well below the yielding levels.