Study of the surface wettability effect on dynamic characteristics of droplet impacting a tube with different curvature ratios

摘要

Surface wettability plays a significant role on the dynamic characteristics of droplet impact. In this paper, five different wettability surfaces are prepared for experiments by dislocation-selective chemical etching and surface modification, three of which are mainly discussed. The corresponding apparent contact angles are 13 degrees, 107 degrees, and 153 degrees, respectively. The dynamic processes of droplets impacting the hydrophilic, hydrophobic and super-hydrophobic tubular surfaces with the impact velocity of 0.94 m/s are observed by high speed photography. The effect of surface wettability on droplet impact is analysed with the curvature ratios of 1.4, 0.43, and 0.26, respectively. It is found that the increase of the curvature ratio hinders rebound but promotes the break-up of the droplet. When the curvature ratio is a constant, poor surface wettability hinders droplet spreading, but promotes retracting and rebounding; An interesting phenomenon is found that, when the contact angle is a constant, the maximum spreading factor increases firstly and then decreases with the increase in the curvature ratio, i.e., there is a critical curvature ratio for each contact angle.