Modeling and Validation of a Membrane Humidifier for PEM Fuel Cell Systems

Abstract

In PEM fuel cell applications the humidification of the inflowing air is of significance since the electrical conductivity of the membrane and consequently the stack performance strongly depends on the water loading of the electrolyte. In this context a detailed dynamic simulation model describing a conventional passive membrane humidifier was developed and imple-mented into MATLAB/Simulink at the Institute of Technical Thermodynamics of the German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR) in Stuttgart. The humidifier model is generally based on a finite volume approach balancing energy and mass flow along the main flow path for both wet and dry fluids. For the description of the heat flux a setting of stirred batch reactors was assumed. The energy transfer between the two flows is accomplished using the humidifier membrane as connecting element and thermal mass. The freely adjustable connection sequence of the single reactors allow furthermore for parallel-, counter- and crossflow configuration. The determination of the water exchange stream is carried out by a separate membrane submodule applying also a finite volume approach. The water concentration and loading difference between the flows and within the membrane define therein the driving force for the water diffusion. The water transfer is directed perpendicular to the main flow path.