Performance and thermal impact analysis of single cell solid oxide fuel cell by utilizing different fuels and its upgradation to stack level
Chaudhary, Tariq Nawaz
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A numerical model of a single planar and stack of solid oxide fuel cell (SOFC) is developed by coupling dynamics of electrochemical reacting flows, heat transfer, and thermal impacts (thermal strains and stresses) of solid electrolyte and porous electrodes for analysing the cell performance. The model is tested and the simulation results of hydrogen fuel SOFC performance are verified with the bench mark data of International Energy Agency (IEA) for co-flow case. Modelling results from test cases show that the coupling is necessary as the electrochemical and thermal properties of the cell strongly depends on temperature. The thermal strains and stresses generated in the cell are then predicted by implementing the temperature profile obtained from the decoupling (the thermal properties of materials are independent of temperature) and coupling simulations. The distributions of thermal strains and stresses, from which the locations with higher values are identified, provide data for optimizing design of SOFC. The thermal impacts of the cell are investigated by employing alternative fuels such as methane. The methane steam reforming (MSR) and water gas shift (WGS) reactions are strongly temperature dependents and play the key role on both the cell performance and thermal impacts. It has been found that temperature decreases along the main flow direction because of MSR reactions dominancy. The thermal strains and stresses generated in methane based SOFC are less than those by hydrogen fed SOFC if both operate to produce identical power. The parametric study is performed to investigate the effect of operating conditions such as inlet temperature, flow rates, flow configurations (co-flow and counter flow), geometrical parameters (porosity, change in cell thickness), and operating voltage on the cell performance and thermal impact. It has been identified that the inlet temperature has significant effect on the cell performance and thermal impact. The co-flow configuration offers better thermomechanical stability. The higher operating voltage results in lower thermal strain and stress generation. The methane fuel model is upgraded to the stack level and the performance of the 8 cells connected in parallel flow configuration has been investigated. The effect of Lanthanum Chromite interconnect between two cells on the cell performance has been analysed by investigations of the distributions of chemical species, reaction rates, temperature, and thermal strain and stress for each cell. It has been recognized that the difference in the performance of the bottom and top cells as compared to the cells in between them is high because of the presence of the interconnect. The temperature distribution along the stack height is non-uniform which leads to non-uniform thermal strain and stress generation. The non-uniform thermal strain and stress generation increases the possibilities of the cell failure which must be taken into account for cell design and operation monitoring.