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Vibration-Induced Droplet Atomization (VIDA)

A liquid drop placed on a vibrating diaphragm bursts into a fine spray of smaller secondary droplets if it is driven at the proper ‘high’ frequency and amplitude.  The process begins when capillary waves appear on the free surface of the drop and then grow in amplitude and complexity as the acceleration amplitude of the diaphragm is slowly increased from zero.  When the acceleration of the diaphragm rises above a well-defined critical value, small secondary droplets begin to be ejected from the free-surface wave crests.  Then, quite suddenly, the entire volume of the drop is ejected from the vibrating diaphragm in the form of a spray.  This event, coined as ‘drop bursting’, takes a fraction of a second and is the result of an interaction between the fluid dynamical process of droplet ejection and the vibrational dynamics of the diaphragm.  As the driving amplitude is increased from zero, the drop exhibits several transitions to states of increasing spatio-temporal complexity.  The first state of the forced drop consists of harmonic axisymmetric standing waves that are present for even the smallest diaphragm motion.  As the forcing amplitude increases above a critical value, a parametrically driven instability results in the appearance of subharmonic azimuthal waves along the contact line.  For larger values of the forcing amplitude, the azimuthal waves couple with the harmonic axisymmetric waves to produce a striking lattice-like wave pattern.  With a further increase in the forcing amplitude, the lattice mode disappears and the interface evolves into a highly disordered state dominated by subharmonic wave motion.  Finally, as the forcing amplitude increases above another critical value, the interface breaks up via droplet ejection from individual wave crests.


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Supported by DARPA and NSF