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Acoustic emulsification. Part 1. The instability of the oil-water interface to form the initial droplets

Published online by Cambridge University Press:  19 April 2006

M. K. Li  and
H. S. Fogler
M. K. Li
Affiliation:
Department of Chemical Engineering, University of Michigan, Ann Arbor Present address: General Electric Corporate Research and Development, Schenectady, New York.
H. S. Fogler
Affiliation:
Department of Chemical Engineering, University of Michigan, Ann Arbor
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Abstract

A technique has been developed to study the phenomenon of ultrasonic emulsification in which oil is dispersed as a fine suspension into water at 20 kHz. It was found that the emulsification takes place in two stages. In the first stage, oil droplets of the order of 70 μm are formed from the instability of interfacial waves. In the second stage these large droplets are successively broken into small droplets by cavitation until a stable droplet size is reached. In this paper, the criterion for the instability of the interfacial waves is developed from a linearized stability analysis of the planar oil-water interface exposed to acoustic excitation. The characteristic droplet diameter produced by the instability is related to the induced capillary wavelength at the interface.

The amplitude of the ultrasonic transducer and the theoretical amplitude of vibration necessary for the instability of the interfacial waves were found to be in agreement. In addition, the sizes of the large droplets present in the suspension systems at short irradiation times agree closely with the predicted droplet diameters.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 88 , Issue 3 , 13 October 1978 , pp. 499 - 511
Copyright
© 1978 Cambridge University Press

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