Dynamics and ice-restraint mechanism of droplet impact on micro-nano structured surfaces

Addressing the icing problem on aircraft surfaces and internal engine structures in aviation, as well as meeting the practical need for developing passive anti-icing and de-icing technologies, the study systematically investigated the dynamic processes of droplet impact on low-temperature horizontal and inclined micro-nano structured surfaces. The study was achieved through a combined approach of experimental research and theoretical derivation. Based on the energy conservation equation, the influence mechanisms of surface micro-nano structures, surface temperature, and impact velocity on droplet impact patterns, spreading coefficients, and freezing time were elucidated. A predictive model for the maximum droplet spreading coefficient were established. Research findings indicate that low-temperature surfaces inhibit droplet rebound. As temperature decreases, droplet impact patterns sequentially exhibit complete rebound, partial rebound, and deposition. When the surface temperature is above -5 ℃, droplets first spread before retracting, with micro-nano structures significantly reducing droplet spreading coefficients. When the surface temperature is below -5 ℃, droplets enter the freezing stage after reaching maximum spreading, and the spreading coefficients increase initially before stabilizing. During the freezing stage, the spreading coefficient increases as the surface temperature decreases. The maximum spreading coefficient of droplets on low-temperature surfaces follows a one-half power law with Weber number. Micro-nano composite structures exhibit stronger delaying capabilities against droplet freezing compared to micro surfaces. Increasing the surface inclination angle, raising surface temperature, and reducing the droplet Weber number can effectively prolong the droplet freezing time.