Optimising acoustic cavitation for industrial application

Yusuf, Lukman Aminu (2022) Optimising acoustic cavitation for industrial application. PhD thesis, University of Glasgow.

Abstract

The ultrasonic horn is one of the most commonly used acoustic devices in laboratories and industry. For its efficient application to cavitation mediated process, the cavitation generated at its tip as a function of its tip-vibration amplitudes still needed to be studied in detail. High-speed imaging and acoustic detection are used to investigate the cavitation generated at the tip of an ultrasonic horn, operating at a fundamental frequency, f0, of 20 kHz. Tip-vibration amplitudes are sampled at fine increments across the range of input powers available. The primary bubble cluster under the tip is found to undergo subharmonic periodic collapse, with concurrent shock wave emission, at frequencies of f0/m, with m increasing through integer values with increasing tip-vibration amplitude. The contribution of periodic shock waves to the noise spectra of the acoustic emissions is confirmed. Transitional input powers for which the value of m is indistinct, and shock wave emission irregular and inconsistent, are identified through Vrms of the acoustic detector output. For cavitation applications mediated by bubble collapse, sonications at transitional powers may lead to inefficient processing. The ultrasonic horn is also deployed to investigate the role of shock waves in the fragmentation of intermetallic crystals, nominally for ultrasonic treatment of Aluminium melt, and in a novel two-horn configuration for potential cavitation enhancement effects. An experiment investigating nitrogen fixation via cavitation generated by focused ultrasound exposures is also described. Vrms from the acoustic detector is again used to quantify the acoustic emissions for comparison to the sonochemical nitrite yield and for optimisation of sonication protocols at constant input energy. The findings revealed that the acoustic cavitation could be enhanced at constant input energy through optimisation of the pulse duration and pulse interval. Anomalous results may be due to inadequate assessment for the nitrate generated. The studies presented in this thesis have illustrated means of improving the cavitation efficiency of the used acoustic devices, which may be important to some selected industrial processes.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Prentice, Dr. Paul and Lucas, Prof. Margaret
• Date of Award: 2022
• Depositing User: Theses Team
• Unique ID: glathesis:2022-82763
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 28 Mar 2022 15:14
• Last Modified: 08 Apr 2022 16:42
• Thesis DOI: 10.5525/gla.thesis.82763
• URI: https://theses.gla.ac.uk/id/eprint/82763

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