The Generation of Cavitation for the Removal of Fouling on Submerged Structures Using High Power Ultrasonic Transducers

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The accumulation of fouling is a well-known problem in industry which can occur on various different structures depending on the surrounding environmental conditions.The removal of this fouling can be very costly and has resulted in many attempts to mitigate, monitor and remove fouling accumulation in a cost-effective manner. As mitigating techniques cannot guarantee 100% fouling removal of a structure, another approach is to detect and monitor the fouling accumulation to assist in carrying out de-fouling procedures. Current detection methods such as PIGging can also require halts in production to carry out monitoring. In recent years, the application of Ultrasonic Guided Waves (UGW) for fouling detection has been recognised as a promising and non-invasive technique; however, its research is still in its early stages. To complement a non-invasive fouling detection technique, the application of ultrasounds has gained much attention from the industry for in-situ fouling removal. Much research has been conducted to advance the knowledge on the potential uses of ultrasonics across different fouling applications, primarily in reverse osmosis membranes and heat exchangers. However, the optimisation of in-situ ultrasonic fouling removal has not yet been investigated and is also in its infancy. This thesis elaborates on the fundamentals of High Power Ultrasonic Transducers (HPUT) used for generating acoustic cavitation bubbles for achieving ultrasonic cleaning. This knowledge is used in the development of a Finite Element (FE) model which is validated using experimental characterisation of the impedance. The HPUT FE model is used to further understand the design and development of sonotrode attachments for future improvements of the ultrasonic cleaning technique. The FE model is expanded for the prediction of cavitation generation to determine cleaning patterns and is validated in laboratory conditions. By utilising controlled fouling generation capabilities, fouling detection using UGW is investigated and an FE model is used to further characterise variables that can quantify the detection of fouling accumulation with potential applications of monitoring fouling removal. The FE method for fouling removal predictions is used to optimise a HPUT configuration for achieving long-distance fouling removal coverage on a 6.2 meter long, 6 inch schedule 40 carbon steel pipe. The confirmed 4-HPUT configuration is developed for laboratory validation and demonstrates wave propagation up to 3 meters from a single HPUT location