SONOLUMINESCENCE IN LIQUIDS UNDER VARYING CONDITIONS THESIS submitted for the Degree of Doctor of Philosophy in the University of London and the Diploma of Membership of the Imperial College. Robert David Finch, M.Sc. February 1963. ABSTRACT A study has been made of the sonoluminescence and of the cavitation produced by a magnetostrictive window-type transducer coupled to a double quarter wave horn. The effect of excess static pressure, applied by gas and also hydraulically, on sonoluminescence of tap water has been imestigated in the range from 0 - 100 p.s.i. An optimum value of hydraulically applied pressure for maximum yield of sonoluminescence, and a higher value at which sonoluminescence was almost suppressed were established. The values of static pressure at which the light yield was a maximum and a minimum both varied with the applied acoustic power. Similar results were obtained with applied gas pressure except that the pressure corresponding to maximum luminescence was displaced on de-pressurising. This hysteresis effect is believed to be correlated with variations in the nucleation of the liquid. Some evidence of this corr. Jlation is afforded by corresponding measurements of the variations of acoustic power absorbed, of the resonant frequency and of the number of sonoluminescence pulses. By taking photographs of single sweep oscilloscope traces, sono- luminescence pulses were found to occur always at roughly the same phase of the sound cycle, but not with every sound cycle, the frequency of their occurrence being random. Photographs of many sweep oscilloscope traces showed a statistical averaging process whereby the sonoluminescence appeared as a discrete pulse with every sound cycle, as found by other authors, Evidence: of the high pressures arising from cavitation was obtained using "carbon paper pressure detectors". Curves of temperature v. time during cavitation showed the presence of a periodic oscillation, particularly pronounced in carbon tetrachloride. A comprehensive review of the literature on sonoluminescence and allied topics is given, and a discussion of the origin of sonoluminescence is appended. It is shown that the differences in 'sonoluminescence yields from a liquid saturated with various gases can be accounted for qualitatively in terms of the ratios of specific heats, the molecular velocities , the solubilities and the excitation potentials of the gases concerned. ACKNOWLEDGEPENTS The author is indebted to many people for their assistance in the work described in this thesis, In particular he wishes to thank Dr. R.W.B. Stephens for his very helpful supervision, and Mr. E. A. Neppiras for generously given advice on numerous theoretical and experimental aspects of the subject. My grateful thanks are due to the Admiralty for the financing of the research and to Messrs. Mullards for the loan of a transducer. I should also like to express my gratitude to various members of the workshop staff and in particular to Mr. T. Shand, Mr. A. Davis and Mr. O.R.Milbank for their most helpful cooperation in the design and manufacture of parts of the apparatus. I record also my thanks for the useful, candid comments freely given by other members of the Acoustics Group. The skill of Mr. E. Sparkes in photographing some difficult subjects was much appreciated. Finally the author wishes to record the patient assistance of his wife in producing this thesis. "Particles of Light appeared plentifully, about the bigness of small pinheads, vory vivid, resembling bright twinkling stars ti Francis Hauksbee, 1709. CONTENTS Page No. CHAPTER I : Survey of Sonoluminescence and Other Cavitation Phenomena. 1.1* Introduction. 1.1.1. Definitions and Historical Review. 1 1.1.2. Instrumentation of Observing Sonoluminescence. 2 1.2. Dependence of Sonoluminescence on Various Parameters. 1.2.1. Frequency. 6 1.2.2. Acoustic Power and Pressure. 7 1.2.3. Static Pressure. 9 1.2.4. Temperature. 10 1.2.5. Time. 12 1.2.6. Physical Properties of the Liquid. 19 1.2.7. Physical Properties of the Solute Gas, 26 1.3. The Spectra of Sonoluminescence. 28 1.4. Sonoluminescence in Hydrodynamic Cavitation. 31 1.5. Light from Collapsing Bubbles. 1.5.1. Light from Agitated Mercury. 33 1.5.2. Collapsing Glass Spheres. 35 1.5.3. Implosion of Bubbles by Shock Waves. 38 1.6. Theories of Sonoluminescence. 38 1.7. Other Effects of Cavitation. 43 I.7.1. Chemical Effects. 44 1.7.2. Erosion. 46 1.7.3. Biological Effects. 47 References in Chapter 1. 49 CHAPTER 2 : Apparatus and Preliminary Experiments. 2.1. Objectives. 2.2. Transducer and Velocity Transformer 53 2.3. Energising Circuit. 57 2.4. Some experimental Observations of Cavitation. 63 Page No. CHAPTER 2 2 -contd. 2.5. Measurement of Acoustic Power. 73 206. Preliminary Observations of Sonoluminescence:.. 82 2.7* The Housing and Sample Holder. 84 2.8. Detecting System. 88 References in Chapter 2. 93 CHAPTER 3 s Observations of the Dependence of Sonoluminescence upon Static Pressure. 3.1, Hydraulic Application of Pressure. 97 3.2. Application of Air Pressure. 109 CHAPTER 4 : Discussion of Experimental Results. 4.1. Observations of Cavitation. 122 4,2. Changes in Noise Level and Temperature Oscillations. 124 4.3. Preliminary Observations of Sonoluminescence. 126 4.4. Variation of Sonoluminescence with Static Pressure. 4-4.1. Theories. 126 4,4.2. Discussion of theories. 129 4.4.3. A Modified Theory. 132 References in Chapter 4. 137 PlOWW1010 ..... CHAPTER 5 : Sugrestions for Further Work. 5.1. Sonoluminescence and Nucleation Problems, 138 5.2. The Origin of Sonoluminescence. 140 References in Chapter 5. 141 Mel 011.11.04.11.••••••.••••••••• 1/•malmarlimi.m. •••1•.••11.11, APPENDIX 1 : Thermal considerations in the design of the sample holder. 142 APPENDIX 2 : A PROPOSED THEORETICAL EXPLANATION OF SONOLUYJNESCENCE AND ASSOCIATED EFFECTS. Page. A.2.1. Introduction. 145 A.2.2. Basic Features. 145 A.2.2.1. : Cavitation Bubble Dynamics. 145 A.2.2.2. : Pressure Distribution. 147 A.2.2.3. : Temperature Distribution. 150 A.2.2.4. : Mass Transfer. 151 A.2.3. The Effect of Thermal Conduction Losses. 151 A.2.4. The Effect of Mass Transfer. 161 A.2.4.1. : In the Bubble Growth. 162 A.2.4.2. : In the Bubble Collapse. 166 A.2.5. The Mechanism of Sonoluminescence 170 A.2.6. The Mechanism of Chemical Effects. 174 A.2.7. The Role of the Liquid in Sonoluminescence. 178 A.2.8. The Effect of Dissolved Salts on Sonoluminescence. 180 A.2.9. The Effect of Organic Additives on Sonoluminescence.182 REFERENCES in Appendix 2. •• APO .. 184 GLOSSARY .. •• •• 186 LIST OF SYMBOLS . •• 188 LIST OF FIGURES. NO: Page 1 Luminescence in water solutions, as a fune'on of !ound intensity 8 2 Relatlon between sonoluminescence and 2 VT 8 3 Sono:Luminescence of water as a function of applied pressure 11 Temperature dependence of sonoluminescence 4 from various aqueous solutions 11 5 Schematic rpresentation of time effects 13 6 Relaxation time variation of sonoluminescence 13 7 Apparatus of Meyer and Kuttruff 16 8 Growth and collapse of cavitation bubbles 17 Volume change of cavitating bubbles and 9 sonoluminescence 20 10 Sonoluminescence as a function of physical properties of liquids 23 11 Sonolumin.sscence as a function of electrolytes dissolved in water 25 12 Spectra of sonoluminescence 31A 13 Radiation strength of light impulses from collapsing glass spheres as a function of filling gas and pressure 37 14 Radiation strength of light impulses from collapsing glass spheres as a function of immersion liquid 37 15 Horn and transducer 16 Circuit for impedance loop measurements 58 INTO s Page. 17 Impedance loop bo 18 Limiter 62 19 Driving voltage as a function of limiter voltage 64 20 Block diagram of driving circuit 65 21. Mounting of crystal pick-up 66 22 Photograph of cavitation 67 23 Construction of carbon paper pressure detectors 70 24 Photograph of exposed carbon paper pressure detectors 71 25 Photograph of atomisation of a water droplet 74 26 Photograph of atomisation of a flow of water 75 27 Glass calorimeter 76 28 Calibration of thermocouple 77 29 Heating curves (water) 78 30 Acoustic power as a function of pick-up voltage 80 31 Heating curves (carbon tetrachloride and glycerine) 81 32 Oscillograph traces of, pick-up voltage and photomultiplier anode voltage (many sweep) 83 33 Oscillograph traces of pick-up voltage and photomultiplier anode voltage (Many sweep) 83 34 Oscillograph traces of pick-up voltage and photomultiplier anode voltage (Single sweep) 85 35 The Housing 87 36 Spectral sensitivity of photomultiplier 89 37 Potential divider 90 No2 Page 38 Integrator 91 39 Circuit for calibration of integrator 92 40 Calibration of integrator 94 41 Photograph of general assembly 96 42 Sonoluminesconce as a function of hydraulically applied excess pressure (6.5 watts) 99 43 Acoustic power absorbed as a function of hydraulically applied excess pressure 100 44 Sonoluminescence as a function of hydraulically applied excess pressure 102 45 Sonoluminescence as a function of hydraulically applied excess pressure (pick—up voltage constant) 103 46 Sonoluminesconce as a function of hydraulically applied excess pressure (8.2 watts) 104 47 Sonoluminescence as a function of hydraulically applied excess pressure (6.95 watts) 105 48 Sonoluminescence as a function of hydraulically applied excess pressure (5.2 watts) 106 49 Sonoluminescence as a function of hydraulically applied excess pressure (power values in region for which optimum excess static pressure = 0 p.s.i.) 107 50 Sonoluminescence as a function of hydraulically applied excess pressure (3.3. watts) 108 51 Shift of maximum with power 110 52 Shift of suppression point with power 111 53 Sonoluminescence as a function of gas applied excess pressure (6.5 watts) 112 54 Sonoluminescence as a function of gas applied excess pressure (5.4 watts) 113 NO: Page.