Study of the oscillations of drops of newtonian liquids induced by acoustic vibrations

Abstract

The aim of this paper is to verify the applicability of the Rayleigh-Lamb equation to drops having different diameters and, specifically, with diameters of the order of magnitude of centimeters (macro drops), millimeters or micrometers (micro drops). On this purpose three experiments have been taken into account. A completely new fact is constituted by the following question: it is possible to apply the Rayleigh-Lamb equation to a heterogeneous drop like that represented by a soap bubble, characterized by a surface tension different from the substance constituting the drop’s mass (air)? The results reported in this paper seem to confirm that this is possible. The order of magnitude of the calculated autofrequencies is comparable to that observed experimentally. The limitations of the experiments are the geometry of the system. The Rayleigh-Lamb equation applies, strictly speaking, to a free drop not subjected to the action of external forces. This would be possible through the use of special devices, i.e the Acoustical Levitated. Therefore, it was decided to carry out the experiments with drops bound by viscous adhesion to the respective supports. It is evident that the geometry of the drop is no longer perfectly spherical, however the results obtained do not seem to have suffered greatly from this limitation.