Hydrothermal waves in evaporating sessile drops (APS 2009)

TL;DR

This study uses infrared imaging to observe the complex heat transfer and convection patterns during the evaporation of sessile drops, providing insights into the mechanisms involved.

Contribution

It presents high-resolution infrared videos revealing internal convection cells and heat transfer processes in evaporating sessile drops, advancing understanding of evaporation mechanisms.

Findings

Identification of convection cells inside evaporating drops

Observation of heat transfer coupling between phases

Insights into evaporation rate variability

Abstract

This fluid dynamics video was submitted to the Gallery of Fluid Motion for the 2009 APS Division of Fluid Dynamics Meeting in Minneapolis, Minnesota. 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 microns of resolution to observe the evaporation of sessile drops in infrared wavelengths. The range of 3 to 5 microns is adapted to the fluids observed which are ethanol, methanol and FC-72 since they are all half-transparent to the infrared.