A non-invasive optical technique to map acoustic cavitation activity

This paper proposes a development of a non-invasive measurement system to monitor acoustic cavitation within a reactor vessel. The measurement technique will detect acoustic emission using an optical approach based on Laser Doppler Velocimetry (LDV). In this study, a LDV scanned the acoustic field in a Perspex walled vessel and characteristic signatures such as the fundamental frequency, harmonics, sub-harmonics and the high frequency acoustic emission associated with cavitation have been identified in the frequency domain and used to provide a measure of the strength of the cavitation activity. It has been proposed that the components are generated by acoustic emission from cavitation bubble. In particular, the amount of acoustic cavitation activity is calculated by a broadband integrated noise power within the frequency range between 1 MHz to 8 MHz. The excitation transducer was a 40 kHz Tonpilz device to generate cavitating field and cavitation was measured across a range of excitation power levels corresponding to 10 – 40 W. The measured results clearly illustrate ‘hot-spots’ and ‘cold-spots’ associated with the regions of cavitation and were verified using a conventional aluminium foil erosion test.