Dynamics of ultrasonic atomization of droplets

We investigate the atomization behavior of a droplet subjected to ultrasonic substrate vibration experimentally. High-speed imaging is employed to quantify the average atomization lifetime of the droplet as a function of initial droplet size and different fluid properties. Atomization rate increases with the initial droplet size and is also found to be very sensitive to changes in viscosity, while not so sensitive to surface tension changes. A theoretical model based on capillary wave breakup mechanism is developed, predicting these trends accurately. Our results underscore the role of capillary wave generation at the liquid-vapor interface via Faraday excitation in ultrasonic atomization. Though the capillary wavelength follows the inviscid scaling law, the wave breakup is shown to be controlled by a viscous-inertia balance.