Model Based Investigation of Liquid Water Injection Strategies for Evaporatively Cooled PEM Fuel Cells

Abstract

Evaporative cooling through liquid water injection directly into the fuel cell flow channels removes the requirement for external humidification and liquid cooling channels within the stack. However, the amount of liquid water injected must be accurately controlled, to prevent on one hand membrane drying due to lack of water vapor and on the other hand flooding due to excessive liquid water. In this paper a one-dimensional, non-isothermal model of an evaporatively cooled proton exchange membrane fuel cell (PEMFC) is produced. The model accounts for changes in relative humidity and temperature along the anode and cathode flow channels, water transfer through the membrane and liquid accumulation within the gas diffusion layers. The model was used to study liquid water injection strategies at both cell and localized level. The influence of current density, operating pressure and inlet humidity were investigated. Results show that provided high humidity is maintained throughout the cell, exhaust gas temperature increase from low to high current densities (0.4–1.4A/cm2) is less than 4.0°C, without the need for active temperature control. Furthermore both temperature regulation and good membrane hydration can be managed by uniform injection of liquid water throughout the cell to maintain a target cathode exhaust humidity.