Mathematische Modellierung von Niedertempertur-Brennstoffzellenstapeln

The simulation tool presented in this work develops descriptions of the most relevant processes in polymer electrolyte fuel cells into a model of a complete fuel cell stack. Using a finite volume method, the fluxes of mass, heat and charge across the electrolyte membrane are modelled in an integral form. The model includes several mechanisms for water transport in the membrane, gas-phase mass transport limitations in the diffusion layers as well as gas flow distributions in cell and stack. The water transport model was compared to measurements performed on a laboratory cell. The simulation results show that the current density distribution is determined mainly by membrane water content, superimposed by oxygen depletion. The model is used to examine the influences of flow patterns, pressure, gas concentrations and membrane properties as well as flow field and manifold geometries. Temperature distribution is most important, since even slight temperature differences have a strong influence on water management. Superposition of temperature effects and non-uniform gas flow distribution can cause local minima in current density. Comparison with a current density distribution determined experimentally shows that the model predicts current density distributions well even for large, technically relevant cell sizes