Session: 10-10-03: Industrial Flows - III

Paper Number: 71972

Start Time: Tuesday, 10:45 AM

71972 - Droplet Dynamics in Pem Fuel Cell Flow Channels 

Proton exchange membrane (PEM) fuel cells benefit from high operating efficiency and zero-carbon emission. In these energy systems, hydrogen is used as the fuel and oxygen is used as the oxidizer. The two byproducts of the electrochemical reactions are heat and water. The produced water in the cathode side passes through the electrode and enters the cathode flow channels in forms of emerged droplets from the surface of the gas diffusion layer (GDL). For a continuous and reliable operation of PEM fuel cells, accumulated liquid water contents in the flow channel should be carefully removed from the flow channel. Otherwise, such droplets can grow in size and block transport of the reactant gas in the flow channel. The inertia and viscous effects from the core gas flow try to transfer the droplet to an unstable state where it detaches from the surface of the GDL. However, such forces should overcome the contact angle hysteresis which tends to hold the droplet on the surface of the GDL. In this study, dynamics of droplets during emergence and growth is investigated by high-speed imaging. For this purpose, air is supplied into a flow channel while liquid water is injected to the surface of the GDL. Droplet’s dynamics is visualized as it grows on the surface of the GDL within the flow channel. The visualization is done in a side-view angle. Therefore, droplet’s contact angles as well as its height and chord length is identified in this study. The emerged droplet deforms in the flow channel to adjusts its geometry with the viscous flow. In this process the surface tension forces pin the droplet to the surface of the GDL and prevent droplet removal from its emergence location. During early experiments, it was observed that droplets oscillate on the surface of the GDL as they grow in size. For low gas flow rates in the channel, the droplet growth is followed by its spread on the hydrophilic surfaces of the channel. The contact line between the droplet and the solid surface should be carefully studied to identify the location at which depinning occurs. In addition, the advancing and receding contact angles should be identified for different gas flow rates in the channel. This study identifies which part of the contact line depins first on the surface of the GDL. In addition to the contact angle hysteresis, droplet height and chord length is measured as the droplet grows on the surface of the GDL. Droplet oscillation frequency and mode is investigated in details.

Presenting Author: Mehdi Mortazavi Western New England University

Authors:

Mehdi Mortazavi Western New England University
Vedang Chauhan Western New England University
Taylor Pedley Western New England University
Brian M. Whinery Western New England University