Hydrodynamics of evaporating sessile drops

TL;DR

This paper investigates the complex hydrodynamic behavior of evaporating sessile drops, detailing the evolution of vortex structures driven by Marangoni convection, thermal conduction, and vapor diffusion.

Contribution

It provides a comprehensive analysis of the stages of vortex formation and evolution in evaporating drops, incorporating effects of thermal conduction and vapor diffusion.

Findings

Multiple vortex stages identified during evaporation

Vortex number decreases over time, ending with a single vortex

Vortex structures are controlled by Marangoni cell size

Abstract

Several dynamical stages of the Marangoni convection of an evaporating sessile drop are obtained. We jointly take into account the hydrodynamics of an evaporating sessile drop, effects of the thermal conduction in the drop and the diffusion of vapor in air. The stages are characterized by different number of vortices in the drop and the spatial location of vortices. During the early stage the array of vortices arises near a surface of the drop and induces a non-monotonic spatial distribution of the temperature over the drop surface. The number of near-surface vortices in the drop is controlled by the Marangoni cell size, which is calculated similar to that given by Pearson for flat fluid layers. The number of vortices quickly decreases with time, resulting in three bulk vortices in the intermediate stage. The vortex structure finally evolves into the single convection vortex in the drop, existing during about 1/2 of the evaporation time.