Numerical study on dynamic behaviours of a micro-droplet impacting on a vertical wall in PEMFC

Abstract

The droplet/wall interaction in the gas channel (GC) of proton exchange membrane fuel cells (PEMFCs) has significant influence on water management, which may affect the performance and durability of the cell. In this paper, a coupled level-set and volume-of-fluid (CLSVOF) method is used to simulate the dynamic behaviours of a micro-droplet impacting on a vertical wall in the GC. The effects of impact velocity (expressed by the Weber number, We), and impact angle on the spreading dynamics are evaluated. Next, the critical conditions for the transition from spreading to rebound are further discussed. For 0 < We < 80, only the spreading, retracting, and rebound are observed, and the phenomenon of air bubble entrapment is captured on different wettable walls. With an increment of We, the maximum total spreading factor l∗ tot and corresponding normalised time t∗ will increase, as well as the normalised time difference Δτ2 between the maximum spreading length and minimum height. Moreover, when increasing the impact angle, the maximum front spreading factor depending on the tangential velocity component will decrease, while the absolute value of maximum back spreading factor squeezed by the normal velocity component will increase. For the oblique downward impact, the front liquid led by the tangential velocity component plays a more important role in dominating the spreading process. The results also indicate that both the wall wettability and We can affect the transition threshold. When the static contact angle is between 90° and 150°, the effect of We on the rebound is inversely proportional to the hydrophobicity of the wall.