Optimierung des Wasserhaushalts eines PEM-Brennstoffzellenaggregats (English shop)

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Climate protection, the undesirable dependence on fossil fuels, and society’s vital interest in reducing energy consumption through greater efficiency while maintaining prosperity in the face of rising oil prices are decisive factors in favour of the sustainable use of energy. The trend towards sustainable mobility has prompted Volkswagen AG to develop the polymer electrolyte membrane (PEM) fuel cell drive in the course of the electrification of vehicles.

The aim of the present work is to optimise the water management of Volkswagen AG’s HyMotion4 fuel cell system, with a focus on the membrane humidifier, the removal of condensate from the flow channels of the fuel cells, and the condensate separator.

The membrane humidifier enriches the reaction air with water separated from the exhaust air. By means of the method presented, which combines Computational Fluid Dynamics (CFD) simulations with experiments, the permeability of the humidifier membranes to water is determined. The permeability, dimensionless numbers, and the characteristic operating conditions of the fuel cell system yield the humidifier geometry and its flow resistance. On the basis of the size and the flow resistance, the investment and operating costs of the humidifier are calculated and minimised.

Excessive humidification of the reaction air, load changes that lead to pressure variations, and the inhomogeneous gas supply to the fuel cells in the stack can result in the condensation of water vapour within the cells. The pressure difference required to remove the condensate is calculated using the CFD method, taking adhesion into account. From the pressure difference, the required flows of reactant gases are calculated which ensure the removal of condensate and consequently stable operation.

On the anode side, the discharged condensate droplets are separated from the hydrogen flow by the condensate separator, since the anode exhaust gas is mixed with fresh hydrogen and the entry of condensate into the fuel cells impairs the reaction. The axial condensate separator is likewise optimised with regard to separation efficiency, size, and flow resistance using the CFD method.