Freezing morphologies of impact water droplets on an inclined subcooled surface

Freezing of impact water droplets is ubiquitous in nature. Prior studies mostly focus on the freezing shapes of droplets impinging perpendicularly to a cold surface. In this work, we investigate how the frozen morphologies of impact water droplets are formed on a subcooled inclined (45 degrees) surface. To en-hance the coupling between droplet impact dynamics and solidification, we hereby conduct the exper-iments on superhydrophilic surfaces under various substrate temperatures (-45 degrees C < Ts <-25 degrees C) and droplet impact velocities (1.33 m/s < V 0 < 3.96 m/s) where the cooling rate is significantly improved. In-triguingly, we discover four types of frozen droplet morphologies, namely elliptical cap, half ring + cap I , half ring + cap II , and half ring + single ring, depending upon the impact velocity and substrate temper-ature. The formation of such morphologies resulted from the competition between the timescales associ-ated with droplet solidification and impact hydrodynamics are appreciably altered by the inclined impact due to symmetry breaking as compared to the normal impact. To unravel the underlying physics, based on scaling analyses we propose a phase diagram to show how frozen morphologies are controlled by droplet impact and freezing related timescales, and find that such phase diagram can corroborate with the experimental findings. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study investigates how the frozen morphologies of impact water droplets are formed on a subcooled inclined surface. Four types of frozen droplet morphologies were discovered, and a phase diagram was proposed to show how frozen morphologies are controlled by droplet impact and freezing related timescales. The competition between droplet solidification and impact hydrodynamics timescales are altered by the inclined impact.