Dynamics of Droplets in Core Gas Flow Superimposed With Acoustic Pressure Waves

Abstract

During the operation of a proton exchange membrane fuel cell, water is produced in the cathode electrode. Accumulation of produced water in the flow channel can block the transport of reactants, which ultimately lowers the performance of the cell. The water content in the flow channel can be efficiently removed from the channel with an external excitation. Previously, the author reported utilization of acoustic pressure waves in order to remove the water content from the flow channel [1]. However, the dynamics of liquid water droplets during this removal process were not investigated. The current study investigates dynamics of water droplets on the surface of the gas diffusion layer (GDL) when acoustic pressure waves are superimposed on the core gas flow. Two different modes of superimposition were implemented; (i) continuous, and (ii) on demand. Study of droplet dynamics was achieved by visualizing the droplet from the side-view with a high-speed camera. When the superimposition was done in the continuous mode at 20 Hz, the droplet went through the rocking motion on the surface of the GDL. For 60 and 80 Hz of superimposition, in addition to the rocking motion, droplets underwent the prolate mode of oscillation, which was characterized by vertical oscillations. For higher frequencies of acoustic pressure waves, in addition to rocking and prolate modes of oscillation, droplets underwent the oblate mode of oscillation, which featured horizontal oscillations. The on on demand experiments demonstrated that the liquid water droplet detached from the surface of the GDL only when the droplet size was large enough.