How supercooled superhydrophobic surfaces affect dynamic behaviors of impacting water droplets?

Water droplet icing on the supercooled surface is ubiquitous and presents gigantic harmfulness on the power transmission lines, aircraft and outdoor equipment. Therefore, a good understanding of droplet impact and freezing process on the supercooled superhydrophobic surface is crucial. In this paper, aluminium sheet was adopted as the substrate to prepare the superhydrophobic (SH) surface. A high-speed camera was applied to explore the dynamic behaviors of a water droplet impacting on the SH surface with various supercooling degrees visually. Moreover, the droplet spreading factor, dimensionless height, characteristics time, rebounding energy and mass fraction of the secondary droplets were adopted to reflect the dynamic behaviors. The results indicate that the dynamic behaviors of a droplet (with an initial temperature of 15 °C, equivalent diameter of 2.94 mm and impacting velocity of 0.99 m·s−1) impacting on the SH surface (160° in static contact angle) with a lower supercooling degree is consisted of three regimes: spreading, retraction and rebounding. Whereas, the retraction and rebounding regime are limited at −17 °C and −24 °C, respectively. Moreover, in the retraction regime, the governing factor of the droplet frozen onset time transforms from the interface heat transfer ability into incubation time at the surface temperature below −34.4 °C. Furthermore, the droplet separating and rebounding are prevented once the remaining energy at the end of the retraction regime is lower than 35% of the droplet initial energy.