A study of cluster cavitation erosion using electrochemical, physical and high-speed imaging techniques

Abstract

Cluster cavitation erosion, generated by piston-like emitter (PLE) vibrating at ultrasonic frequencies, was measured using a novel aluminium erosion sensor in conjunction with optoisolation techniques, in order to bridge the electrochemical detection of cavitation erosion with a counting device possessing USB connectivity, while minimising electrical noise. High-speed imaging assisted in correlating the periodicity of cluster collapse with the frequency of erosion events detected by the sensor. The consistency of the shape and duration of current-time transients associated with erosion were shown to be dependent on drive voltage amplitude and drive frequency of the PLE.

Erosion in the presence of silicon carbide particles, agitated by the PLE, was measured in an identical manner. Cluster cavitation dynamics were shown to be affected by the presence of silicon carbide, making it difficult to ascertain whether erosion events were due to silicon carbide grazing the sensor surface or whether the events were bubble-driven. Subsequent high-speed imaging and analysis of the shapes of current-time transients, suggested that under certain experimental conditions, erosion of the sensor surface could be attributed to silicon carbide particles.

Analysis of the acoustic noise spectrum generated during inertial cavitation showed that an increase in the magnitude of the 2f component and the presence of the f/2 component corresponded with the onset of non-inertial bubble collapse and inertial cavitation erosion respectively. However, no subsequent correlation could be made between the magnitude of the f/2 component and the extent of erosion detected. Measurements from both a hydrophone and microphone gave similar results.

The effect of a liquid’s physical properties on the sonoluminescence intensity was investigated by analysing the results of prior studies and experiments conducted here using an image intensifier. Sonoluminescence intensity was found to increase with normal boiling point of a liquid assuming identical experimental conditions (drive frequency, voltage, ambient temperature), and provided the boiling point did not exceed c. 200 oC.

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Identifiers

ORCID for Peter R. Birkin: orcid.org/0000-0002-6656-4074

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