Numerical investigations of water droplet dynamics in micro-channels considering contact angle hysteresis

The volume of fluid (VOF) method coupled with a contact angle model considering hysteresis effects is used to study the dynamic of water droplets in micro-channels for proton exchange membrane fuel cells. The contact angle hysteresis is modeled by a modified third-order fit relationship for the contact angle and the azimuthal angle. Droplets sliding down the smooth surface, textured surface and carbon paper are firstly solved as examples to evaluate the accuracy of the numerical model to predict the adhesion force. The effects of channel geometry and contact angle hysteresis on the dynamic of water droplets in micro-channels are investigated. Geometrical study reveals that the gap between the droplet and channel wall is an important factor influencing the drag force. Due to the low contact angle of the channel side wall, the droplet at the corner have larger detachment velocity than the droplet at the middle of the channel. The numerical results for the effects of contact angle hysteresis indicate that the changes of the contact angle hysteresis and wetting area both result in the variation of the adhesion force and account for the variation of the detachment velocity.