The implications of water and thermal management parameters in the optimization of an indirect methanol fuel cell system

Effective water and thermal management of a fuel cell system is essential in achieving high overall efficiency and maintaining water self sufficiency. A proton exchange membrane fuel cell system that runs on steam-reformed methanol presents interesting water and thermal management challenges. The first part of the paper briefly describes the key aspects of the water and thermal management (WTM) model developed as part of the Fuel Cell Vehicle Modeling Program (FCVMP) at the University of California-Davis. The main objective of the model is to satisfy the temperature and water management requirements of the system with the least possible parasitic load. This model has imbedded in it all the relevant components of the fuel cell system, such as the fuel cell stack, air compressor and fuel processor as seen by the WTM system. The impact of cathode pressure and cathode stoichiometry on water recovery is analyzed and the "cost" of maintaining water self-sufficiency under different operating air supply conditions is discussed. It is shown that shifting the condensing load from the condenser to the stack can potentially decrease the WTM parasitic loads. One of the other interesting results of the model is that cooling and humidification of the anode and cathode streams can be done in one step by water injection thereby doing away with heat exchangers for that process.