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Title: Cavitation phenomena in liquids subjected to tension by dynamic stressing
Author: Brown, S. W. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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This thesis describes the development of new techniques for the study of cavitation phenomena which arise when liquids are subjected to dynamics stressing by tension. The first of these techniques addresses the measurement of the tensile strength (Fc) of a liquid under dynamic stressing. Unlike previous work in this area, the method reported herein eschews the direct measurement of tension by pressure transducers. Rather, Fc is estimated from measurements of the velocity of tension pulses whose amplitude is sufficient to cause cavitation. The tension pulses used in this work involve stressing rates of ca. 1 bar/μs and have characteristic times of ca. 2 x 10-4s. Contrary to previous indications in the literature, this form of stressing does not result in anomalously low values of Fc for water, with values recorded herein (up to 700 bar) representing the highest reported under low frequency ultrasonic stressing. These results are in accordance with expectation given the dependence of Fc on the timescale of stressing. The second technique reported herein facilitates studies of the interaction of a cavitation-generated shockwave with a gas bubble near a free surface. Such a situation may arise in biomedical applications of ultrasound. The present study shows that the impingement of the shockwave on the bubble causes a liquid jet to form. This jet is directed towards the free surface from which it extends as a filament. Work is reported in which the influence of fluid elasticity markedly reduces the velocity of the jet and its ultimate length. Finally, a method is presented for estimating the resistance to uniaxial extension of the filaments. For a Newtonian liquid the Trouton ratio is 3 but in experiments involving bubble collapse in dilute polymer solutions the Trouton ratio was in the range 200-500, indicating a significantly enhanced resistance to extensional flow in these solutions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available