Dependence of fluid flows in an evaporating sessile droplet on the characteristics of the substrate

TL;DR

This study uses detailed numerical calculations to explore how substrate properties influence vortex structures in evaporating sessile droplets, revealing controllable fluid flow patterns.

Contribution

It demonstrates that substrate thermal properties can be used to control vortex structures in evaporating droplets, supported by phase diagrams and numerical analysis.

Findings

Thermal conductivity ratio affects vortex number and orientation.

Substrate thickness influences vortex formation.

Fluid flow can be controlled by substrate selection.

Abstract

Temperature distributions and the corresponding vortex structures in an evaporating sessile droplet are obtained by performing detailed numerical calculations. A Marangoni convection induced by thermal conduction processes in the drop and the substrate is demonstrated to be able to result not only in a single vortex, but also in two or three vortices, depending on the ratio of substrate to fluid thermal conductivities, on the substrate thickness and the contact angle. The "phase diagrams" containing information on the number, orientation and spatial location of the vortices for quasistationary fluid flows are presented and analysed. The results obtained demonstrate that the fluid flow structure in evaporating droplets can be influenced in a controlled manner by selecting substrates with appropriate properties.