Numerical Analysis on Water Droplet Dynamic Behavior in A Cathode Channel Under Low Frequency Vibration
The fundamental dynamic behavior of a liquid water droplet in a cathode channel of PEMFC under low frequency vibration was investigated with the assistance of computational fluid dynamics. The detachment size, the departing time, and the moving speed of liquid water droplets were compared to non-vibration condition by varying frequency, displacement amplitude, initial phase, water droplet growth speed, system installation, and surface contact angle. The vibration frequency and displacement amplitude were selected by considering the operating condition of transportation and stationary power generation applications. The VOF method was used to trace the gas-liquid interface change and the moving boundary was introduced to simulate the dynamic behavior of vibration in a three dimensional numerical domain. Parametric studies reveal that individual liquid water droplet may show diverse behavior even at the same operating condition due to its growth rate and generation mechanism. Overall, 20% detachment time reduction and 10% liquid water droplet size decrease are detected in most cases but it also shows as much as 200% departure time delay for horizontal installation. The effect of frequency, displacement amplitude, water droplet growth speed, and surface contact angle does not show strong relationship with the dynamic behavior of liquid water droplets because the considered frequency range is far lower than the resonance frequency of a liquid water droplet.
Keywords: PEMFC, Cathode channel, two-phase flow, CFD, VOF, vibration