Feasibility study of removal of surface contaminants from solid surfaces using water jets with bubbles and ultrasound

FEASIBILITY STUDY OF REMOVAL OF SURFACE CONTAMINANTS FROM SOLID SURFACES USING WATER JETS WITH BUBBLES AND ULTRASOUND MUHAMMAD FADZLI B HASSAN NATIONAL UNIVERSITY OF SINGAPORE 2013 FEASIBILITY STUDY OF REMOVAL OF SURFACE CONTAMINANTS FROM SOLID SURFACES USING WATER JETS WITH BUBBLES AND ULTRASOUND MUHAMMAD FADZLI B HASSAN (B.ENG (HONS), NATIONAL UNIVERSITY OF SINGAPORE) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 I Declaration I hereby declare that this thesis is my original work and it has been written by me in its entirety I have duly acknowledged all the sources of information which have been used in the thesis This thesis has also not been submitted for any degree in any university previously _ Muhammad Fadzli Bin Hassan 09 May 2013 II This thesis incorporates content from the following publications: Hassan, M F., Lee, H P., & Lim, S P (2010, May) The variation of ice adhesion strength with substrate surface roughness Measurement Science and Technology, 21, 1-9 Hassan, M F., Lee, H P., & Lim, S P (2012) Effects of Shear and Surface Roughness on Reducing the Attachment of Oscillatoria sp on Substrates Water Environment Research 84 (9), 744 – 752 Hassan, M F., Lee, H P., & Lim, S P (2012) A Semi-Empirical Analysis of the Formation of Equilibrium Bubbles from Submerged Needle Manifolds at Low to Moderate Gas Flow Rates Physics of Fluids Under review; manuscript number MS #12-1056 Hassan, M F., Lee, H P., & Lim, S P (2012) A semi-empirical analysis of the effects of needle bore and flow rate in pneumatic retinopexy Eye Under review; manuscript number EYE-12811 III Acknowledgements I would like to express my profound gratitude and regards for my supervisors, Associate Professor Lee Heow Pueh and Associate Professor Lim Siak Piang for giving me this wonderful opportunity to conduct research in the field of contaminant control using bubbles and ultrasound I sincerely thank them for all their guidance and advice, academic-related and otherwise, during my time at the National University of Singapore I would also like to thank Associate Professor Sigurdur Thoroddsen for his guidance in the early stages of my studies, Professor Khoo Boo Cheong for his valuable input on bubble dynamics as well as the staff of the Tropical Marine Science Institute for giving me guidance on microalgae cultivation and research as well as allowing me the use of their facilities My profound gratitude also goes to the National Research Foundation (Environmental Water Technologies) scholarship board for their generous financial support without which my graduate research work would not have been possible Finally, I would like to thank my parents and my wife for their encouragement and support in making this work possible IV Table of Contents Contents V Summary X List of Tables XII List of Figures XIV List of Symbols XIX Introduction 1.1 1.2 Surface foulants and contaminants Objectives and scope of Work Investigation I: Adhesion of Ice to Solid Substrates 2.1 Introduction 2.1.1 An introduction to surface roughness 2.2 Literature survey 10 2.3 Current investigation 11 2.4 Preparation of aluminium samples 17 2.5 Experimental procedure 21 2.6 Analysis 25 2.7 Computer simulations 26 V 2.8 2.9 Discussion and limitations 29 Conclusions 31 Investigation II: Adhesion of Microalgae to Stainless Steel 3.1 3.2 Shear stress 36 3.3 Materials and methods 37 3.4 Results and discussion 49 3.5 Introduction to Oscillatoria sp microalgae 34 Conclusion 57 Investigation III: The Effects of Ultrasound on Microalgae 4.1 Introduction 60 4.2 Literature review 61 4.2.1 The agglomeration of microalgae by ultrasound 61 4.2.2 The mechanical vibration of microalgae by ultrasound 62 4.2.3 The lysing of microalgae by ultrasound 65 4.2.4 Surface roughness effects on the sonication of microalgae biofilms 66 4.3 Preliminary experiment: The agglomeration of microalgae suspensions by ultrasonic waves 67 4.3.1 Preliminary experiment: Procedure 70 4.3.2 Preliminary experiment: Results 71 4.3.3 Preliminary experiment: Laser vibrometer readings 75 4.3.4 Preliminary experiment: Pressure distribution measurement 76 VI 4.3.5 Discussion 80 4.4 The effects of ultrasound on algae biofilms: experiment 81 4.4.1 Experimental setup and procedure 81 4.4.2 Experimental results 85 4.4.3 Visualization of water flows induced by ultrasound 89 4.4.4 Discussion 92 4.5 Conclusion 92 Investigation V: The Measurement of Impact and Shear Stresses of Impinging Equilibrium Bubbles 5.1 5.2 The quantification of impact and shear forces via direct measurement 96 5.3 Calibration of PVDF film 99 5.4 Materials and methods 102 5.5 Experimental results 104 5.6 Discussion 108 5.7 Introduction 95 Conclusion 110 Investigation VI: The removal of surface foulants and contaminants from an etched surface with bubbles and ultrasound 6.1 The removal of microalgal biofilms by non-cavitating bubbles 112 6.1.1 Introduction 112 6.1.2 Literature review 113 VII 6.1.3 Materials and methods 114 6.1.4 Experimental Results 121 6.1.4.1 Macro scale analysis 121 6.1.4.2 Micro scale analysis 122 6.1.5 The removal of microalgal biofilms by equilibrium bubbles on a large scale over a prolonged period of time 125 6.2 The removal of microalgal biofilms by non-cavitating bubbles with ultrasound 131 6.2.1 Introduction 131 6.2.2 Theory of ultrasound on bubble dynamics 131 6.2.3 Experimental setup and conditions 134 6.2.4 Experimental results 138 6.2.5 Conclusion 140 Conclusion 7.1 Introduction 142 7.2 Investigation I: Adhesion of Ice to Solid Substrates 143 7.3 Investigation II: Adhesion of Microalgae to Stainless Steel 144 7.4 Investigation III: The Effects of Ultrasound on Microalgae Suspensions and Biofilms 145 7.5 Investigation IV: The Measurement of Impact and Shear Stresses of Impinging Bubbles 146 7.6 Investigation V: The removal of surface contaminants from an etched surface with bubbles and ultrasound 148 7.7 Final Remarks 150 VIII Appendix I: The Production of Bubbles from Submerged Needle Nozzles A.1 Introduction 152 A.2 Literature survey 153 A.3 Important bubble parameters 155 A.3.1 Capillary length, a 155 A.3.2 Bubble surface area A and characteristic diameter di 156 A.3.3 Bubble shapes 156 A.3.4 Characteristics of a one-dimensional bubble plume 158 A.3.5 Sauter-mean diameter, dSM 160 A.3.6 Plume Reynolds number, ReP 160 A.4 Theoretical Analysis 161 A.4.1 Slow bubbles Stage I: Formation of bubble at the capillary tip 161 A.4.2 Slow bubbles Stage II: Rise and Detachment of Bubble 163 A.4.3 Fast bubbles Stage I: Formation of bubble at the capillary tip 166 A.4.4 Fast bubbles Stage II: Rise and detachment of bubble 167 A.5 Solutions of theoretical analysis 170 A.5.1 End of Stage I 170 A.5.2 End of Stage II 171 A.6 A.7 A.8 Experimental analysis 173 Experimental results 174 Conclusion 180 References 182 IX Investigation IV: The Production of Bubbles from Submerged Needle Nozzles APPENDIX I corresponds to a diameter of 2.255 mm This diameter is two orders of magnitude greater than the 205 μm reported by the authors It may be argued that the observations of Parini and Pitt are the result of the breakup of large bubbles into smaller satellite bubbles However, for such a condition to occur, the original bubbles would have to be very large to begin with Wichterle et al (2005) claimed that the minimum bubble volume for spontaneous breakup in water is 0.2 cm3, which corresponds to a minimum bubble diameter of 7.26 mm For such large bubbles to be formed, a flow rate of over 700 ml/min has to be passed through the 25G needle The breakup also tends to be chaotic, with some bubbles breaking up and others failing to so The bubbles that break up would tend to split into two similarly-sized bubbles, each of which having a volume of around half of that of the original bubble With all these points in mind, it appears to be highly unlikely for bubbles on the order of hundreds of micrometers to be in diameter to be formed through this mechanism As the experimental analysis is both time- and labour-intensive, we have thus far tested this theoretical model for only four orifice diameters, and for flow rates only up to 48 ml/min The theoretical analysis could also be further refined by factoring in the compressibility of the air flow, particularly at low flow rates Further experimental investigations into other orifice diameters are needed to aid in the validation of this model In the meantime, the applications of this particular investigation have been applied to another field of research apart from the current overarching investigation into the removal of surface contaminants Pneumatic retinopexy is an ophthalmic surgical procedure for sufferers of minor rhegmatogenous retinal detachment (Conolly and Regillo 2009) This surgical procedure involves the injection of a small gas bubble directly into the eyeball using a 25G, 27G, or 30G 181 Investigation IV: The Production of Bubbles from Submerged Needle Nozzles APPENDIX I needle (Bourla et al 2007) The gas bubble floats upward and pushes the detached retina back into place Between 0.3 and 0.5 ml of gas is injected into the eye while the patient is lying supine Ideally only one large bubble should result from the injection as multiple small bubbles may lead to deleterious consequences for the patient (Mohamed and Lai 2000) The results of the investigation in this chapter found that every needle gauge had its own minimum gas bubble volume below a flow rate of 10 ml/min, and that a needle with a larger internal diameter would produce larger bubbles for the same flow rate We applied these findings to conclude that the optimum way of conducting pneumatic retinopexy was by injecting the gas as quickly as possible using the coarsest needle that could be tolerated by the patient without any harmful physical effects The investigation on bubble production in this chapter has since been sent to Physics 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The Measurement of Impact and Shear Stresses of Impinging Bubbles 146 7.6 Investigation V: The removal of surface contaminants from an etched surface with bubbles and ultrasound ... Investigation VI: The removal of surface foulants and contaminants from an etched surface with bubbles and ultrasound 6.1 The removal of microalgal biofilms by non-cavitating bubbles 112 6.1.1 Introduction