Spreading of a droplet impacting on a smooth flat surface: how liquid viscosity influences the maximum spreading time and spreading ratio

TL;DR

This study investigates how liquid viscosity affects droplet spreading on smooth surfaces, introducing a viscosity-inclusive model that accurately predicts maximum spreading time and ratio across diverse fluids.

Contribution

The paper presents the first viscosity-based model for maximum droplet spreading time, improving prediction accuracy over existing models by incorporating fluid viscosity effects.

Findings

Model accurately fits experimental data across various fluids.

Viscosity significantly influences maximum spreading time.

Incorporating viscosity improves model predictions for droplet impact.

Abstract

Existing energy balance models, which estimate maximum droplet spreading, insufficiently capture the droplet spreading from low to high Weber and Reynolds numbers and contact angles. This is mainly due to the simplified definition of the viscous dissipation term and incomplete modeling of the maximum spreading time. In this particular research, droplet impact on a smooth sapphire surface is studied for seven glycerol concentrations between 0% - 100%, and 294 data points are acquired using high-speed photography. Fluid properties such as density, surface tension, and viscosity are also measured. For the first time according to the authors' knowledge, we incorporate the fluid viscosity in the modeling of the maximum spreading time based on the recorded data. We also estimate the characteristic velocity of the viscous dissipation term in the energy balance equation. These viscosity-based characteristic scales help to formulate a more comprehensive maximum droplet spreading model. Thanks to this improvement, our model successfully fits the data available in the literature for various fluids and surfaces compared to the existing models.