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Title: The formation and activity of bubbles during cavitation produced by dynamic stressing
Author: Williams, P. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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This Thesis contains an account of theoretical and experimental work in which the origin and development of the cyclic pressure-tension cycles associated with cavitation phenomena in liquids are investigated and, for the first time, fully explained. The activation phenomena studied herein involve the growth and collapse of cavitation bubbles in a liquid which is subjected to dynamic stressing by pulses of tension. The dynamic stressing apparatus developed in the course of this work is described in Chapter 2 and is a development of that used by Chesterman (1952) and Overton and Trevena (1981). Chapter 3 contains an account of the improvements made to this apparatus and the ancillary pressure recording and high-speed photographic equipment. Contrary to previous indications in the literature, the theoretical work described in Chapter 4 shows that the pressure waves ascribed by previous workers to the collapse of cavitation bubbles actually originate in the growth phase of the bubbles during their rebound from minimum radius. Using a hydrodynamic argument, based on incompressible theory, it is also shown that the tension waves appearing in the cyclic pressure-tension records were wrongly ascribed in previous work to the attainment of maximum bubble radius and that these tension waves originate in an earlier stage of he deceleration of the bubble's surface. The experimental work described in Chapter 5 was designed to test the hypothesis that inadequacies in the pressure transduction technology used in previous dynamic stressing experiments had resulted in a failure to record the shockwaves expected to accompany cavitation bubble collapse. Using the improved apparatus described herein those shockwaves are recorded, as are their reflections, as pulses of tension, from the free surface of the liquid sample (water). High speed photography was used to confirm that cavitation accompanied these tension pulses and an important finding, reported herein for the first time, is that these tension pulses travel not at the expected value of the velocity of sound in liquid water but at a velocity appropriate to water-vapour. The later finding is exploited in the work described in Chapter 6 in order to estimate the effective tensile strength of water from measurements of tension pulse velocity. The results obtained, which yield an effective tensile strength of ca. 600 bar, are commensurate with the lower values in the range of theoretical estimates (Temperley, 1947). A further development of this work involving the reflection of compressional waves as tension is described in Chapter 7, that describes experiments in which the interface between two immiscible liquids is subjected to dynamic stressing. The results obtained support the idea that a layer of vapour, formed by cavitation, can act to reflect subsequent compressional waves incident upon it, as tension. Further, these results support the conclusion drawn by Couzens and Trevena (1974) that the maximum tension which the interface between two immiscible liquids can sustain is less than that which can be sustained by either liquid alone. The significance of the findings reported in this Thesis to certain aspects of engineering and biomedicine is discussed in Chapter 8 and recommendations for further work in this field are made.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available