Abstract: In order to achieve good stack water chemistry and minimize corrosion in a fuel cell stack water cooling loop, the oxygen concentration in the water must remain within a relatively narrow range. Stacks using steam separators produce water in the separators which is relatively devoid of oxygen. Makeup water is used to replace the steam lost from the separator, which makeup water is relatively rich in oxygen. The flow rates of the makeup water and steam separator water are controlled to produce a proper oxygen concentration in the recirculated coolant water. Some of the makeup water will be added directly into the steam separator so that it will be stripped of oxygen and the rest will be added subsequent to the steam separator.

Abstract: Fuel Cell stack coolant water is processed by moving the two-phase water/steam coolant exhaust through a steam separator wherein the water phase is separated from the steam phase. The water phase is then moved through a heat exchanger where its temperature is lowered to a subcooled level which is below the coolant operating temperature in the stack. A flow control valve is associated with the coolant heat exchanger to regulate water flow through and/or around the heat exchanger depending on the temperature of the water which leaves the steam separator. By subcooling the coolant before it reenters the stack, a lessening of electrolyte loss through evaporation is achieved. By eliminating steam condensation as a form of system heat rejection, system engineering is simplified and construction costs are lowered.