Dissolution dynamics of a vertically confined sessile droplet

Area of Science:

• Fluid dynamics
• Mass transport phenomena
• Microscale phenomena

Background:

• Microscale droplet dissolution is crucial in various applications.
• Understanding dissolution under confinement is key to controlling processes.
• Previous studies often neglect the impact of specific confinement geometries.

Purpose of the Study:

• To experimentally investigate the dissolution of microscale sessile alcohol droplets in water under vertical confinement.
• To identify and characterize the flow mechanisms hindering dissolution within confined environments.
• To develop modified scaling laws for droplet dissolution that incorporate confinement geometry.

Main Methods:

• Experimental investigation of microscale sessile alcohol droplet dissolution.
• Flow visualization techniques to observe fluid dynamics.
• Analysis of morphological changes and mass transport.
• Development and validation of modified dimensionless parameters (Rayleigh number, Sherwood number) and droplet lifetime.

Main Results:

• Confinement suppresses mass transport compared to nonconfined droplets.
• A levitated toroidal vortex was identified as a key mechanism impeding dissolution.
• The vortex alters dissolution rates, significantly enhancing droplet lifetime.
• Experimental data corroborated proposed scaling relations: Sh′∼Ra′^(1/4) and τc′∼ΔC′^(-5/4).

Conclusions:

• Vertical confinement significantly alters microscale droplet dissolution dynamics.
• The levitated toroidal vortex is a critical factor in reducing dissolution rates and extending droplet lifetime.
• The proposed modified scaling laws, incorporating confinement geometry, are applicable to various channel dimensions and configurations.
• Findings have implications for microfluidic technology, biomedical engineering, and other fields involving confined multiphase flows.