Experimental study on dynamics and freezing characteristics of droplet impact on supercooled surfaces

Abstract

Droplet impact freezing is a natural phenomenon that significantly affects infrastructure and human activities. Despite extensive research on the effects of various parameters on droplet impact and freezing processes, there remains a lack of comparative analysis regarding the degree of influence of these parameters on the impact process, as well as insufficient thermodynamic analyses of the freezing process. This paper experimentally compares the effects of droplet sizes (2.28 mm–3.10 mm), Weber numbers (15–35), and surface temperatures (−30 °C–20 °C) on impact dynamics, including maximum spreading factor and receding ratio, on hydrophilic and superhydrophobic surfaces. The results show that on hydrophilic surfaces, the maximum spreading factor of droplets is significantly influenced by both the Weber number and surface temperature, while on superhydrophobic surfaces, the Weber number plays the primary role. Moreover, the maximum spreading factor and receding ratio of droplets on hydrophilic surfaces are notably higher than those on superhydrophobic surfaces, suggesting a faster heat exchange rate on hydrophilic surfaces. To deepen the understanding of the freezing process and the impact of related parameters on freezing time, particularly the evolution of the freezing front over time, we solved the heat conduction equations for various materials under appropriate boundary conditions. Our analysis determined that the freezing thickness scales with the square root of freezing time. Based on these findings, we propose a model to predict the freezing time of finite-thickness ice sheets. The predictions of our model align well with our experimental data and findings from other researchers, which validates its accuracy.