A model based investigation of evaporative cooling for polymer electrolyte fuel cells – System level analysis

Abstract

Evaporative cooling is a promising concept to reduce the fuel cell system volume and mass significantly. This paper investigates the interactions between the fuel cell stack and the balance of plant in an evaporatively cooled polymer electrolyte fuel cell system (PEFCS). For this, a zero-dimensional PEFCS model, comprising the fuel cell stack, air compressor, charge air cooler, humidifier, hydrogen recirculation blower, condensing radiator and water separator has been developed and analyzed. Two evaporative cooling system architectures are compared to conventional, liquid cooling. Optimal operating conditions are determined by a numerical optimization of the net system power output. Main results show that evaporative cooling works on the system level over a wide range of operating conditions. The optimum system power and highest efficiencies are achieved at high temperatures (80–90 °C), low pressure (125–150 kPa) and a corresponding cathode stoichiometry between 1.5 and 3, allowing for a closed water loop at the same time. The air compressor shows an increased power demand, compared to conventional cooling and the exhaust gas condenser is identified as the one critical component for evaporative cooling. Its performance is key to an efficient operation and closed water loop at all ambient conditions.