Characterization of the Temperature Profile near Contact Lines of an Evaporating Sessile Drop

Evaporation of a sessile drop is ubiquitous in nature and has many industrial applications. Despite extensive studies over recent decades, a critical issue, i.e., how temperature varies near contact lines, remains elusive. In this work, we report to date the first direct experimental measurement showing the microscopic temperature distribution near contact lines of an evaporating pinned sessile drop. Using a fluorescence-based thermometry, we find that the temperature at the free interface near contact lines varies drastically along the radial direction, engendering a concentric fringe pattern that evolves over the evaporation lifespan. The formation of such fringe patterns is attributed to a combined mechanism of locally enhanced evaporative cooling at the drop edge and the development of interfacial convective vortices due to Benard-Marangoni instability. We also study the evaporation dynamics at different initial contact angles and find that the characteristics of this fringe pattern vary as the initial contact angle decreases. Our experimental investigation and theoretical analysis in this work reveal insights to the understanding of droplet evaporation dynamics in various heat transfer systems.

Automated summary

In this study, the researchers conducted direct experimental measurements on the microscopic temperature distribution near the contact lines of an evaporating pinned sessile drop. They found that the temperature at the free interface near the contact lines varies significantly along the radial direction, forming a concentric fringe pattern that evolves over the evaporation process. The formation of such patterns is attributed to enhanced evaporative cooling at the drop edge and the development of interfacial convective vortices due to Benard-Marangoni instability. The characteristics of these fringe patterns were found to vary with different initial contact angles. This experimental investigation provides insights into the dynamics of droplet evaporation in various heat transfer systems.