Hydrothermal waves in evaporating sessile drops

TL;DR

This paper investigates the complex heat and fluid dynamics of evaporating sessile drops using advanced infrared imaging to better understand internal convection patterns and evaporation mechanisms.

Contribution

It provides new experimental observations of internal convection cells in evaporating drops through high-resolution infrared imaging, addressing gaps in understanding evaporation processes.

Findings

Identification of hydrothermal waves in evaporating drops

Visualization of convection cells inside the drops

Enhanced understanding of heat transfer during evaporation

Abstract

Drop evaporation is a simple phenomena but still unclear concerning the mechanisms of evaporation. A common agreement of the scientific community based on experimental and numerical work evidences that most of the evaporation occurs at the triple line. However, the rate of evaporation is still empirically predicted due to the lack of knowledge on the convection cells which develop inside the drop under evaporation. The evaporation of sessile drop is more complicated than it appears due to the coupling by conduction with the heating substrate, the convection and conduction inside the drop and the convection and diffusion with the vapour phase. The coupling of heat transfer in the three phases induces complicated cases to solve even for numerical simulations. We present recent experimental fluid dynamics videos obtained using a FLIR SC-6000 coupled with a microscopic lens of 10 micron of resolution to observe the evaporation of sessile drops in infrared wavelengths. The range of 3 to 5 micron is adapted to the fluids observed which are ethanol, methanol and FC-72 since they are all half-transparent to the infrared.