Abstract

Nebulisers are used for the delivery of fine droplets of drugs to the lungs or smaller bronchii. An ultrasonic nebuliser uses the oscillations caused by a piezoelectric crystal to produce a "fountain" in a liquid, which leads to the formation of a mist of fine particles. This work describes a model of an ultrasonic nebuliser, with the aim of demonstrating the mechanism of the fountain formation. It is shown that the oscillating ultrasound causes a mean flow in the liquid due to acoustic streaming, which in turn creates a deformation of the free surface. Cavitation within the liquid, which is an energy intensive process, leads to the dissipation necessary for acoustic streaming to occur. Finally, a mechanism for explaining the location of the mist on the free surface is proposed, based upon the results.

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