Solidification dynamic of an impacted drop

TL;DR

This study models and experimentally validates the solidification process of impacting water drops on cold surfaces, revealing the formation of an ice layer that influences the drop's spreading and retraction dynamics.

Contribution

It introduces a 1D solidification model based on the Stefan problem and links it to the observed ice layer formation during drop impact.

Findings

Good agreement between model predictions and ice pancake thickness

Identification of a frozen ice layer pinning the contact line

Derived expression for main ice layer thickness based on impact parameters

Abstract

This paper is dedicated to the solidification of a water drop impacting a cold solid surface. In a first part, we establish a 1D solidification model, derived from the Stefan problem, that aims at predicting the freezing dynamic of a liquid on a cold substrate, taking into account the thermal properties of this substrate. This model is then experimentally validated through a 1D solidification setup, using different liquids and substrates. In a second part, we show that during the actual drop spreading, a thin layer of ice develops between the water and the substrate, and pins the contact line at its edge when the drop reaches its maximal diameter. The liquid film then remains still on its ice and keeps freezing. This configuration lasts until the contact line eventually depins and the liquid film retracts on the ice. We measure and interpret this crucial time of freezing during which the main ice layer is built. Finally, we compare our 1D model prediction to the thickness of this ice pancake and we find a very good agreement. This allows us to provide a general expression for the frozen drop main thickness, using the drop impact and liquid parameters.