Flow structure and evaporation behavior of an acoustically levitated droplet

Abstract

We experimentally investigate the flow structure and evaporation behavior of a droplet in an ∼19 kHz single-axis acoustic levitator. Decane, nonane, octane, heptane, hexane, and pentane are used as test fluids to investigate the effect of saturated vapor pressure on the internal and external flow fields. Under low saturated vapor pressure (decane and nonane), the direction of the external flow is away from the surface of the droplet. However, at a relatively higher saturated vapor pressure (octane, heptane, hexane, and pentane), the direction of the external flow is toward the surface of the droplet, with vortices forming near the droplet surface. For droplets with a low saturated vapor pressure (decane, nonane, octane, and heptane), the internal flow is similar to that in the case of rigid body rotation. Finally, under high saturated vapor pressure (hexane and pentane), the internal flow is an unsteady 3D complex flow. The experimental results indicate that the vapor concentration distribution around a levitated droplet surface correlates closely with changes in the external and internal flows.