不同润湿性表面液滴冻结及融化特性研究

Due to the unique wetting properties of micro-nano structure, superhydrophobic surface has shown wide anti-icing application prospects in many fields such as low-temperature refrigeration. In order to reveal its anti-icing mechanism，in this paper, based on the visualization experiments, the effects of surface temperature and wettability on the freezing and melting process of droplets were studied. The results show that, compared with the smooth aluminum surface, the droplet precooling time, droplet phase transition time and droplet complete melting time are greatly longer on the surface of the square pillar microstructure. In addition, the freezing time of droplet is gradually shortened with the decrease of surface temperature, and the anti-icing performance between them is gradually close. After nucleation and re-calescence, the freezing front gradually rises and finally forms the conical tip with the passage of time. Furthermore, the droplets on the surface of the two samples have the variation law of decreasing contact angle and increasing height. Compared with the smooth aluminum surface, the change of the contact angle of the square-pillar microstructure surface is smaller, and the droplet height increases greatly, showing its stable and unique wettability. Due to the weakening or even destruction of the “air cushion effect”, the surface wettability do not recover immediately after the droplet melt, and the contact angle is smaller than the measured value at room temperature. Moreover, the second freezing time of droplets at different surface temperatures is shorter than the first freezing time, but the delayed freezing performance is still better than that of the smooth aluminum surface. Due to the small superheat of the frozen droplets, when the surface temperature rises to about 2∼3^◦C, the frozen droplets will melt obviously. As the initial melting temperature of the surface decreases, the start melting time gradually increases, while the droplet melting process time is relatively stable and is hardly affected by the initial melting temperature of the surface.