Experimental investigation of the evaporation of droplets in axial acoustic fields

The effect of axial acoustic fields on the evaporation of individual drople ts is investigated bath experimentally and theoretically. A setup was devel oped in which images of droplets moving through an acoustic field were acqu ired using a state-of-the-art, high-speed, intensified video system. The ev aporation rates of droplets were determined from the droplet diameters meas ured from these images. Experimental investigations using methanol droplets showed that the presence of an acoustic field significantly enhances the e vaporation of droplets. The evaporation rate is a strong function of the ac oustic amplitude, but increases only slightly with frequency, The effect of acoustic oscillations on water and methanol droplet evaporation was theore tically modeled by numerically integrating the differential equations for d roplet mass, momentum, and heat transfer. The model uses quasisteady correl ations for momentum heat and mass transfer. The model predicted the measure d trends correctly However, the quantitative agreement of these predictions with the experimental data depends strongly on the correlations for Nussul t and Sherwood numbers used to model the energy and mass transfer, respecti vely.