Effect of temperature difference between impinging droplet and cold superhydrophobic surface on its dynamic behavior

The phenomenon of water droplets impacting on cold surfaces and freezing is common in various fields and has numerous detrimental effects. Meanwhile, superhydrophobic surfaces have received a lot of attention in terms of preventing icing. Therefore, it is important to investigate the dynamic behavior of water droplets impacting on superhydrophobic surfaces in a supercooled environment under different temperature conditions in order to prevent icing. In this study, the dynamic behavior of water droplets impacting on superhydrophobic surfaces in a supercooled environment is visualized using a high-speed camera, and the effect of the temperature difference between the droplet and the cold surface on the dynamic behavior of the impacting droplet is emphatically investigated. The dynamic characteristics of the droplet were also analysed in terms of dimensionless contact diameter, dimensionless droplet height, contact time and energy balance. The results show that the change in properties of the droplet is mainly reflected in the change in viscosity. At low Weber number, the change in viscosity has little effect on the dimensionless contact diameter and contact time but has a significant effect on the dimensionless height of the droplet during retraction. Of particular note is the fact that when the droplet temperature is constant, a decrease in the surface temperature leads to a significant slowing down of the droplet retraction process on the superhydrophobic surface and a significant increase in the contact time. However, a phenomenon contrary to intuition has been observed, namely that a similar situation occurs with increasing droplet temperature when the surface temperature is constant. This behaviour of the droplets is related to the possible existence of liquid-phase condensation processes in the microstructure, and we have also analysed theoretically the conditions under which condensation occurs. This study could contribute to the development of anti-icing technology.