Direct Simulation of Mass Transport in a SOFC Cathode Using Microchannels

Fuel cells are clean and efficient power generation devices which are being widely investigated under the efforts to reduce the impact of greenhouse gases on the environment. Solid oxide fuel cells (SOFCs), especially, are suitable for stationary power generation using a wide range of alternative fuels. Performance of a SOFC strongly depends on the mass transport inside the porous electrodes which are essentially composed of a network of microchannels. In this study the mass transport inside a SOFC cathode is studied using direct simulation of mass transport in microchannels along with statistical analysis. A virtual cathode is built using microchannels that are representative of continuous flow paths between the cathode/air stream interface and cathode/electrolyte interface of a SOFC. Different representative microchannel flow paths are built with varying tortuosity and channel diameters. The numbers of channels of each kind are chosen according to a normal distribution and they are randomly arranged in an appropriately sized cuboid to construct a unit block of the virtual cathode. The normal distribution is modulated with average and standard deviation values for real world electrodes found in literature. Microchannels are tightly packed to achieve the desired porosity. Mass transport in each of the channels is studied separately using commercial CFD software FLUENT. Three dimensional simulations of momentum and specie transport equations (for oxygen and nitrogen) are performed. The results from individual channel simulations are used to assess the global mass transfer characteristics of the virtual cathode. Results obtained using this approach will be compared with those from a continuum Fick’s law type diffusion model used to simulate mass transport in porous media. The primary objective is to test the assumptions employed within the context of continuum mass transport model.