DETERMINATION OF ANODE-PORE TORTUOSITY FROM GAS AND CURRENT FLOW RATES IN SOFCS

The effect of solid oxide fuel cell (SOFC) anode thickness, porosity, pore size, and pore tortuosity on fuel and exhaust gas flow is calculated. Also determined is the concentration of these gases and of diluent gases as a function of position across the anode. The calculation is based on the "dusty-gas" model which includes Knudsen diffusion (wall collision) effects as well as unlike-molecule collision effects in the Stefan-Maxwell equation set. This equation set is solved exactly, avoiding commonly-made approximations such as the assumption of uniform total gas pressure across the anode. The formulae we developed are applied to results of careful experiments performed by another group, who used binary and ternary gas mixtures on the anode side of an SOFC. Our values for tortuosity are in fair agreement, once a difference in nomenclature is taken into account, with those obtained by that group who made some common approximations that we avoided. The nomenclature difference consists in their definition of tortuosity being what some call tortuosity factor, which is the square of what we and others call tortuosity. The results emphasize the need for careful design of anode pore structures, especially in anode-supported SOFC's which require thicker anodes.