Role of melting and solidification in the spreading of an impacting water drop

TL;DR

This study investigates how phase change processes like melting and solidification influence the spreading behavior of water droplets impacting cold surfaces, extending existing models to account for these effects.

Contribution

It introduces a modified scaling law that incorporates phase change effects, providing a universal description of droplet spreading with melting or solidification.

Findings

Maximum spreading increases with temperature and impact velocity.

Solidification reduces spreading due to increased dissipation.

Fusion promotes liquid film spreading, enhancing impact dynamics.

Abstract

The present study reports experiments of water droplet impacting on ice or on a cold metallic substrate, with the aim of understanding the effect of phase change on the impingement process. Both liquid and substrate temperatures are varied, as well as the height of fall. The dimensionless maximum spreading diameter, $\beta_m$, is found to increase with both temperatures as well as with the impact velocity. Furthermore, $\beta_m$ is reduced when solidification, which enhances dissipation, is present, whereas fusion favours the liquid film spreading. These observations are rationalized by extending an existing model of effective viscosity, in which phase change alters the size and shape of the developing viscous boundary layer, thereby modifying the value of $\beta_m$. The use of this correction allows to adapt a scaling law existing for isothermal drop impacts to propose a universal law giving the maximum diameter of an impacting water droplet in the presence of melting or solidification.