How does gravity influence freezing dynamics of drops on a solid surface

TL;DR

This study investigates how gravity affects the freezing dynamics of water droplets on solid surfaces, revealing that initial droplet shape, influenced by gravity, is the key factor controlling freezing behavior and timing.

Contribution

It demonstrates that gravity-induced initial droplet shape determines freezing dynamics, providing a unified understanding of pendent and sessile droplet freezing across different Bond numbers.

Findings

Gravity significantly alters droplet shape and freezing process.

Final frozen droplet height is proportional to initial height.

Freezing time depends on initial geometry and follows a power-law.

Abstract

Water droplet freezing is a common phenomenon in our daily life. In both natural scenarios and industrial production, different surface inclinations bring distinctive deformation and freezing dynamics to frozen droplets. We explore the freezing of pendent and sessile droplets at different Bond number regimes. The effect of gravity on the droplet freezing process is analyzed by considering droplet morphology, freezing front dynamics, and freezing time. It is found that gravity can significantly influence droplet freezing processes via shaping the initial droplet, resulting in the flattening or elongation of pendent and sessile droplets, respectively. We show that the droplet initial geometry is the most important parameter and it completely controls the droplet freezing. Despite the significant difference in the initial droplet shape several remarkable similarities have been found for pendent and sessile droplets at small and large Bond numbers. The final height of a frozen droplet is found to be linearly proportional to its initial height. The time evolution of the ice-liquid-air contact line is found to reproduce the power-law $t^{0.5}$, but noticeably faster than the Stefan 1-D icing front propagation. As a consequence, the time to freeze a droplet is faster than predicted by the Stefan model and it is found to be dependent on the initial droplet height and base radius through a simple power-law.