USE OF EFFECTIVE CONDUCTIVITIES AND UNIT CELL-BASED SUPRAELEMENTS IN THE NUMERICAL-SIMULATION OF SOLID OXIDE FUEL-CELL STACKS

The numerical simulation of current and temperature distribution in mo nolithic solid oxide fuel cell (SOFC) stacks requires fast computers b ecause of the large number of mesh points required in casting a comple x solid geometry into a finite difference form and the necessity to so lve coupled, nonlinear differential equations. By analogy with the mod elling of radiative heat transfer in packed bed reactors, a significan t degree of simplification is achieved by defining effective electric and thermal conductivities for the repeating unit cell elements, ident ified as the basic building blocks of the SOFC stack. The effective co nductivities are approximated by closed form formulae derived from the principles of electrostatics and heat conduction. The effect of radia tion across the gas channels is incorporated into the expressions for the effective thermal conductivity. Using this approach, the unit cell geometry, local mass transfer processes and reaction kinetics are exp ressed in terms of a supraelement model in a finite difference grid fo r the numerical calculation of temperature and potential distributions in a stack by an iterative process. The simplifications thus provided render simulations of three-dimensional SOFC stacks tractable for des ktop processors. By using the foregoing approach to numerical simulati on, a parametric study of a cross-flow type SOFC is presented, and som e of the results are compared with the available experimental data.