Shape Deformation And Atomization Of Functional Droplets In Contact With A Vibrating Surface

We report two kinds of instabilities in the form of secondary atomization and catastrophic breakup in levitated fuel droplets. The short wavelength (Kelvin-Helmholtz) instability for diesel and bio-diesel triggers secondary atomization near the droplet equator. Temperature dependent fuel properties and external heating rate are responsible for the inception and relative strength of these instabilities. If breakup occurs, it is always preceded by secondary atomization when droplet Weber number exceeds a critical value. The second type of instability results from change in surface tension and viscosity with increase in droplet temperature which causes wide fluctuations in droplet aspect ratio. If the viscous damping of aspect ratio oscillation is not strong enough, the droplet goes through unbounded stretching. A stability criterion has been established based on the inhomogeneity of Bernoulli (acoustic) pressure and surface tension of the droplet in terms of a local Weber number and Ohnesorge number. This instability is thermally induced in a droplet which does not experience instabilities without external heating