Numerical analysis of the effect of ellipsoidal shape on the freezing behavior of impacting water droplets on cold surfaces

Abstract

A two-dimensional numerical model that investigates the freezing behavior of ellipsoidal impacting water droplets on cold surfaces was established in this paper, focusing on the spreading behavior, impact force evolution and heat transfer behavior of ellipsoidal water droplets. For cold surfaces with a higher temperature, reducing aspect ratio can reduce the contact time of water droplets on the superhydrophobic surface, which is useful for the rebound of impacting water droplets. Increasing aspect ratio can increase the spreading range of water droplets, especially for hydrophilic surfaces. The evolution of impact force of ellipsoidal water droplets on superhydrophobic surfaces exhibits a double-peak feature. With increase of aspect ratio, the first peak of impact force is gradually decreased, while the second peak is gradually increased. The effect of surface wettability on the first peak of impact force is smaller. The feature of the second peak of impact force decreases with increase of surface wettability and finally disappears. Although water droplet with higher aspect ratio has smaller peak of heat transfer rate, the heat transfer between it and cold surface is greater than that with lower aspect ratio. The stronger the surface wettability, the more obvious this phenomenon is. For some applications where the rapid freezing of impacting water droplets is required, increasing aspect ratio of water droplets seems to be a good choice.