Experimental studies on a liquid ultrasonic cylindrical waveguide

Abstract

This thesis presents research work on an ultrasound assisted stream (UAS) device, commercially known as the “Starstream device”. The UAS device combines ultrasonic energy with a stream of flowing liquid, which could be directed onto target surfaces for contaminant removal. At the start of this project, the focus was towards understanding the response of the device and to improve its performance. Research work thus included studies into acoustic cavitation, capillary instability, electrochemistry & microbubble generation, and transducer design. The required control over flow rate, liquid temperature, and speed of sound was achieved by modifying and upgrading the existing experimental setup. During the experiments, the adverse influence of unwanted microbubbles was successfully reduced by employing an ultrasonic standing wave cylindrical column (called the outgasser). The performance of the outgasser was quantified using acoustic and photographic observations, and its use demonstrated an increase in the pressure output of the device. The non-linear response of the device was quantified and was correlated to the non-linear response of the piezoelectric transducer. The non-linear response was classified into linear, transition, and non-linear regimes. The linear regime of the UAS device was investigated experimentally at resonance at off-resonance frequencies of the transducer, under different loading conditions (air, water, bubble-free liquid, bubbly-liquid). Bubbly-liquid was electrolysed in the liquid stream and the microbubbles generated were optically measured. Discussions of the experimental results were supported by the investigations on the electrical impedance of the transducer by employing lumped-parameter modelling (under different loading conditions). The operation of the device in its non-linear regime was found to be characterized by a novel capillary instability formation of the cylindrical stream. The capillary instabilities were simultaneously investigated using high-speed optical and acoustical techniques at different liquid flow rates, surface tension values, and viscosity conditions. An external technique to control them was successfully implemented. Finally, a combination of experimental kits and techniques reported in the thesis was shown to improve the performance of the existing UAS device.

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ORCID for Timothy Leighton: orcid.org/0000-0002-1649-8750

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