(539f) A Two-Dimensional Dynamic Model for a Tubular Solid Oxide Fuel Cell ( Sofc)

In this talk, we will discuss a detailed two dimensional dynamic model for an anode-supported tubular SOFC. The model includes: (i) mass and momentum transport phenomena in the anode and cathode gas flow channels for reactants and products, (ii) diffusion from the gas flow channels through the porous electrodes to the reaction sites, (iii) activation overpotential through the Butler-Volmer equation with concentration and temperature dependent expression for exchange current density, and (iv) ohmic resistances. The transport equations in the gas channel were reduced to a quasi-2D analysis and both the axial and radial variations were considered inside the electrodes. Step inputs in cell terminal voltage and inlet hydrogen flow rate were introduced and the transient response of the overall system was analyzed. A MAPLE-MATLAB environment was used to yield the transient response for a number of key variables. We will demonstrate the validity of the model using data from a commercial SOFC.

Although a detailed model is absolutely essential to capture the nonlinear characteristics of a SOFC, the computation time is prohibitively high for the model to be used in real-time applications such as control. In this talk, we will also present a reduced order lumped model that can be used in various real-time applications. A lumped model of the same unit cell was simulated in Pspice software. In this model, the reactants and product concentrations were considered only at the inlet and exit of the cell preserving their time-dependence. The partial pressure equations were approximated by an equivalent RC circuit. Substantial simplifications were also done in this model for the calculation of activation and concentration overpotential. An empirical relationship was developed to calculate the limiting current density for the system. Further, an approximation was used to calculate the exchange current density. It is observed that the transient response from the lumped model is in good agreement with the detailed model. Future work will include the use of the detailed model in optimization and the lumped model in control studies.