In the present study, we carried out an experimental investigation of the impinging and freezing processes of a supercooled large water droplet on an ice surface. One high speed camera was used to measure the dynamic motions of the water droplet while two charge coupled device (CCD) cameras were adopted to obtain the images of the freezing process and the freezing morphologies, respectively. The effects of the water droplet temperature and the ice surface temperature on the impact and freezing processes of the water droplet were carefully evaluated. The results showed that the subcooling degree of the water droplet had an apparent influence not only on the spreading process but on the freezing morphology as well. When the subcooling temperature of the water droplet was high (e.g., T_w= –3.0 °C), a triangle cross-section profile formed. However, once the subcooling temperature of the water droplet was relatively low (e.g., T_w= –9.0 °C), the final ice morphology consisted of two parts: one part was a cone-like bead in the center while the other part was an ice ring at the periphery. Moreover, at the same water droplet temperature, raising the ice surface temperature led to an increase in the maximum spreading factor.

In the present study, the impact of a water droplet onto a rotational surface was experimentally studied. The effects of the impact velocity, the rotational speed, and the impact radial position on the impact phenomena were carefully investigated. The phenomena of asymmetric spreading, finger formation, and secondary droplets were observed. Moreover, experiments of a water droplet impacting onto a stationary surface with different impact velocities were also conducted for comparisons. The results showed that, at the same impact velocity, the increase in the rotational speed or the impact radial position could result in the increase in the wetting length in the angular direction and the wetting area. In addition, at the same impact velocity, the dimensionless wetting length in the radial direction on the rotational surface was generally lower than the spreading factor on the stationary surface. In addition, new correlations for the spreading ratio, the dimensionless excess spread area, the dimensionless maximum wetting area, and the number of fingers appearing at the angle of 50° after impact were proposed. The increase in the impact velocity and the surface linear velocity could both promote the formation of the fingers at the angle of 50° after impact. In addition, the dimensionless horizontal displacement of the secondary droplet was found to be mainly influenced by the impact velocity, while the surface linear velocity only had a minor influence.

A droplet impinging on a liquid film finds numerous applications in diverse scientific fields. Although studies have primarily focused on spherical droplets, a droplet can present both spherical shape and non-spherical shape at the moment of impact. In the present study, the impact dynamics of a non-spherical droplet on a thin liquid film is investigated experimentally. The results show that, under the same film thickness and Weber number conditions, the splashing and deposition regimes are different for different droplet shapes such as prolate, sphere, and oblate. It is found that the splashing threshold (Ksp) is changed according to the shape of the droplet. Under the same condition when a spherical droplet is in the deposition mode, an oblate droplet is more likely to splash and form secondary droplets, while a prolate droplet is more splash-resistant even at higher Weber numbers. A modified theoretical model for crown radius evolution is developed. The predictions of theoretical model are found to agree well with the experimental results for spherical and non-spherical droplets. Moreover, at the same Weber number, a prolate droplet has a relatively higher maximum crown height than those of an oblate droplet and a spherical droplet.