Experiments in acoustic levitation: Surface tension and viscosity of deformed droplets.

摘要

Acoustic levitation permits the observation of individual oscillating liquid droplets. Droplet shape oscillation data lead to thermophysical property measurements without the contaminating effects of a solid container. For spherical droplets, analysis has shown natural frequencies are a function of droplet size, mode number, and the surface tension and density of the liquid; the damping rate of oscillations has been correlated with the viscosity of the liquid. In terrestrial levitation, however, gravity serves to deform the droplet and split the frequency spectrum. In addition, droplet evaporation causes natural frequencies to change over time. This work compares experimental data on the frequency splitting of water and ethyl alcohol with theoretical predictions. With slight refinements to the theory, good agreement is found. Surface tension and viscosity were also measured; surface tension for distilled water came within 5% of the published value, and a new approach to the measurement of viscosity via levitation is described and tested.