Evaporation Modeling for Polymer Electrolyte Membrane Fuel Cells

Several methods exist in which evaporation is accounted for in fuel cell modeling. Whether at the system level, the cell level, or at the individual component level, understanding water management is paramount. In order to fully understand water management an understanding of the product water phase is necessary, as the liquid and vapor phase transport quite differently in the porous media and micro-channels. Most of the current literature follows a variation of a few main approaches. A common approach is to create a switch that tells the model whether water is evaporating or condensing. During a simulation the partial pressure of water vapor varies, and as it approaches the saturation pressure evaporation is subsequently turned on or off. Other approaches involve adjusting evaporation rates to keep thermodynamic equilibrium. Many models neglect calculating transient interfacial mass transport all together and only assume a constant evaporation and condensation rate for a transient process.