10. Water Management in Proton Exchange Fuell Cells

After providing the basic thermodynamic and electrochemical laws and relationships, this chapter investigates the impact of reactant humidification for a polymer electrolyte membrane based fuel cell system. As an example, an air humidifier model operated under coflow, counterflow, and crossflow conditions (independent of separator material) is described. The model includes the operation characteristics of a mass exchanger based on three dimensionless parameters: The dimensionless concentration change, the dimensionless transfer capacity (number of transfer units), and the ratio of the volume flow rates. In this model the whole humidification process (governed by humidifier design and separator material properties) is described based on a single characteristic value, the effective mass transfer coefficient. The model provides a deeper understanding and prediction capability of the transfer processes which is helpful for humidifier design, controlling humidifier operation conditions, and might even make sensors unnecessary.