Experimental Investigation of Evaporation from Low-Contact-Angle Sessile Droplets
Date of this Version1-2010
This document has been peer-reviewed.
Evaporating sessile drops remain pinned at the contact line during much of the evaporation process, and leave a ring of residue oil the surface upon dryout. The intensive mass loss near the contact line causes Solute particles to now to the edge of the droplet and deposit at the contact line. The high vapor diffusion gradient and the low thermal resistance of the film near the contact line are responsible for very efficient mass transfer in this region. Although heat and mass transfer at the contact line have been extensively studied, well-characterized experiments remain scarce. The local mass transport in a 100-400 mu m region near the contact line of a water droplet of radius 1810 mu m on a glass substrate is experimentally quantified in the present work. Microparticle image velocimetry measurements of the three-dimensional now field near the contact line are conducted to map the velocity field. Combined with high-resolution transient liquid profile shapes, the measured velocity field yields transient local evaporative mass fluxes near the contact line. The spatial and temporal distribution of the local evaporative flux is also documented. The temperature distribution in the droplet near the contact line is deduced from the local evaporative fluxes and interface mass transport theory.
Engineering | Nanoscience and Nanotechnology