MATHEMATICAL MODELING AND NUMERICAL SIMULATION OF POLYMER ELECTROLYTE MEMBRANE FUEL CELLS

Abstract

Fuel Cells are one of the most promising power generation techniques due to their high efficiency with much lower thermal and acoustic harmful emissions that result - from fuel-air reactions. These cells are also advantageous for their mobility and size flexibility that enable usage in different applications. They are so able to spread over different sites where clean electric power is needed and are thus a reliable alternative to conventional internal combustion engines and steam power plants as well.

In this thesis, a single phase, steady-state, two-dimensional model has been developed to simulate proton exchange membrane fuel cells. The model accounts simultaneously for electrochemical kinetics, hydrodynamics, and multicomponent transport. A single set of conservation equations valid for the heterogeneous domain consisting of the flow channels, gas-diffusion electrodes, catalyst layers, and the membrane region was developed and numerically solved using an in-house CFO code utilizing the efficient PISO algorithm. The numerical solution shed light on the complex electrochemistry• flow/transport interactions in the fuel cell and was used to investigate the effect of the different cell operating conditions like temperature, pressure - and reformate composition (viz. inlet hydrogen percent) on the performance of the fuel cell. The numerical model was validated against published experimental data as well as other - numerical solutions and was found to be in good agreement. The detailed two• dimensional electrochemical and flow/transport simulations further revealed that in the presence of pure oxygen in the cathode stream mass transport limitations (which limit the cell performance) are alleviated leading to increased cell current density and - better performance. - In a like manner but to some lesser extent, the presence of

_ hydrogen dilution in the anode resulted in anode mass transport polarization and hence a lower current density that is limited by hydrogen transport from the anode - stream to the active reaction sites. Eventually, the current density identifying the onset

of two-phase flow regime (which limits the applicability of the present model) is predicted.