(740b) Investigating the Effect of Precursor Composition On the Size Distribution of Droplets Generated by An Ultrasonic Droplet Generator

Ultrasonic atomization processes serve as an important source of monodispersed highly tunable micro and nano droplets for use in a variety of industries. Specifically, common applications include drug delivery, micro and nano materials processing and environmental emulation. The nature of the processes developed provides several distinct advantages over other systems designed to similarly generate droplets. The ultrasonic  generators can be run in parallel to generate large amounts of aerosol.  To fully appreciate this intrinsic value and allow for future applications we have begun developing an understanding of the physics behind the droplet formation process. We have examined the correlation between the surface tension and viscosity of the precursor solutions and carrier gas flow rates on the size distribution of the generated droplets. Our investigation utilized a generator that operates at a frequency of 1.7 MHz, when operating the generator forms a cone with precursor solution, on which the droplets with diameter around 10 microns are formed, probably due to the capillary theory.  Observations from a Malvern/INSITEC system were used to characterize the aerosol droplet size distribution, which revealed an additional, larger size distribution of the droplets under certain design conditions. By manipulating the precursor salt and cosolvent volume percent, one can generate a second mode at 50 microns, and also a lower atomization rate, when a viscosity of at least 3mm/s was measured. The second mode was confirmed through the use of Shadowgraphy:  a high-speed camera and laser illumination source. The images taken indicate that the larger mode was formed via a different process than the current capillary theory indicating the physics of the system are not fully appreciated in the literature.