Modeling of Proton Exchange Membrane Fuel Cell System Considering Various Auxiliary Subsystems

Abstract

In the study, a comprehensive proton exchange membrane fuel cell (PEMFC) system model is developed, including a two-dimensional transient multiphase stack model, a transient membrane humidifier model, air compressor model, and cooling model. The coupled water and heat transport processes, sophisticated water phase changes, gas/liquid transport in porous layers, and flow channels are taken into consideration in the integrated system model. Effects of gas purge duration in PEMFC stack and membrane humidifier on startup performance are investigated under subzero and normal temperatures. It is found that purge duration of membrane humidifier has little effect on output voltage when started from −10 °C and −5 °C since saturated vapor pressure is relatively small. Besides, the cold start duration is mainly determined by initial membrane water content in PEMFC stack. The upstream current density is usually higher because reactant gases are more abundant. To avoid sharp voltage drop during startup from 30 °C with large current density, long purge duration is not suggested for both PEMFC stack and membrane humidifier. The humidifier temperature is stabilized at about 42 °C as a result of exhausted gases heating and heat loss to environment when stack temperature is kept at 60 °C. The membrane water content in humidifier increases more rapidly when current density rises since more water vapor is generated and flows into humidifier; meanwhile, it results in higher humidifier temperature.