Liquid water management in polymer-electrolyte-membrane (PEM) fuel cell reactant channels is critical to system performance, stability, and lifespan. A balance between cathode catalyst layer water generation and removal must be maintained to ensure proper membrane hydration while preventing flooding. Liquid water transport through the gas-diffusion-layer (GDL) results in droplet formation in reactant channels that may be removed via flow gas drag forces. This work investigates the effect that acoustic wave transmission in reactant flow gases has on liquid water droplets growing on the GDL surface. While recent and past work has shown this method may be useful toward preventing liquid buildup in reactant channels, fundamental analysis of the droplet behavior is lacking [1-3]. In this study experiments were performed using a transparent ex-situ flow channel of 3.5 (h) x 3.7 (w) mm cross section as shown in Figure 1a. Water droplet formation was controlled using a digital syringe pump injected through a port on the backside of the GDL. Air and Hydrogen were used to simulate both cathode and anode flow conditions. A speaker was connected in series with the feed gas and flow channel whereby acoustic signals were generated and passed through the reactant channel. Transducers measured pressure upstream and downstream of the droplet while a high speed camera captured images of the droplets motion from the side (Figure 1b). Early results show that pressure waves effect droplets pinning behavior on the GDL surface. Previous work has shown that a maximum contact angle hysteresis exists for droplet removal from GDLs. While gas flow causes droplet contact angle hysteresis, this work shows that oscillations caused by the acoustic waves may shift the droplet over the max hysteresis tipping point enabling removal.

References:

1. M. Schafer, J.S. Allen, Improved water removal from fuel cell flow channels via natural frequency excitation of free surfaces, ECS Transactions 41 (1), 1887-1896, 2011
2. Allen, Jeffrey S., "Water removal from gas flow channels of fuel cells" (2013), Patent#: 8524410, https://digitalcommons.mtu.edu/patents/120
3. Mortazavi, A.D. Santamaria, J.Z. Benner, V. Chauhan, Enhanced Water Removal from PEM Fuel Cells Using Acoustic Pressure Waves, Journal of The Electrochemical Society, 166 (7), F3143-F3153, 2019