Improving water removal efficiency in a PEM fuel cell: Microstructured surfaces for controlling instability-driven pinching

Abstract

Proton Exchange Membrane Fuel Cell (PEMFC) is a clean, sustainable energy generation device, and its large-scale usage is becoming popular due to green and secure energy demand worldwide. The performance, efficiency, and lifespan of PEMFC largely depend on the water removal and management within the cell. Under the influence of the cross-air flow, the generated water filaments deform, and as the filament radius lowers, the curvature and capillary pressure increase, ejecting fluid out of the neck at increasing velocities. The moment the filament radius vanishes, the governing equations reach the point of singularity, and the filament breaks. We propose an optimum micro-patterned surface design for efficient water removal from PEMFC. We perform a numerical study of water generation on the surface followed by breakup under shear flow within confinement. We further theoretically identify the breakup behavior with characterization, recognizing the influence of the microstructures toward an efficient design. The hydrophobic microstructures are observed to decrease the dominance of viscous force over inertia and capillary force. This leads to a greater propensity of end-pinching or truncation of the generated droplet at the neck, which reduces the production of undesired satellite droplets that would have otherwise caused flooding of the chamber. In this work, we show that a proper combination of substrate structure and jet velocity-induced shear can mitigate the generation of satellite droplets and reduce the breakup time, significantly increasing the water removal efficiency of the PEMFC.