Experimental study on contact time of a water droplet impact under controlled surface temperature

Abstract

Bouncing droplets on superhydrophobic surfaces is one of the potential methods used for anti-icing. The surface supercooling is a significant parameter influencing the bouncing dynamic. A droplet impacting cold superhydrophobic surfaces is investigated via experimental methods. The influence of the surface supercooling and the Weber number on the impact dynamic is elucidated. Intriguingly, the surface supercooling shows no influence on the spreading time, and the initial retraction time as the heat exchange can be ignored in these processes, while it shows a strong influence on the late retraction time as it can lead to the wetting transformation. To further quantitatively describe the influence of surface supercooling, the relationships of the retraction rate in the late retraction are developed, considering the changes in the receding contact angle caused by the supercooling degree. Finally, the relationship of the contact time is established over a range of Weber numbers (We = 49.37–70.53), surface supercooling (ΔT = 15–24 °C), and droplet sizes (D0 = 2.2–3.2 mm). This work is the first to establish the relationship of the droplet contact time on cold superhydrophobic surfaces, which can provide a quantitative method to calculate the contact time for anti-icing.