Controllable fuel cell humidification by ultrasonic atomization

Abstract

Compared to the conventional bubble type used for PEMFC (proton exchange membrane fuel cell) humidification, ultrasonic atomization has the advantages of smaller size, it is easy to refill and change temperature, and, more importantly, humidity controllability. To improve the performance of the FC, this study developed a unique ultrasonic atomization system, including a gas heating pipe, ultrasonic driving circuit, ultrasonic atomizer, and humidity sensors. The reactant gases used are hydrogen and air. When the reactant gas obtains sufficient heat from the heating pipe and enters the ultrasonic atomizer, gas humidification is increased due to the ultrasonic micro water droplets blending into the gases. The humidity is controllable by adjusting either the heating temperature or driving voltage. The size of the micro water droplets can also be manipulated by adjusting the driving frequency. A higher driving frequency leads to smaller droplet mean diameter, which in turn increases the humidification efficiency. At least 90% relative humidity can be maintained under the condition that the flow rate of anode and cathode's reactant gas is restricted to between 1LPM and 25LPM. Under the same condition, the conventional bubble type can only achieve around 80%.