Acoustic analysis of vortex-based cavitation devices: inception and extent of cavitation

Hydrodynamic cavitation (HC) is a process of generation, growth and collapse of gas/vapour filled cavities leading to intense shear and localised hot spots. It is essential to identify the inception and extent of cavitation for ensuring appropriate operation of HC devices and processes. In this work, we demonstrate for the first time, usefulness of acoustic data acquired using an everyday mobile phone for characterising inception and extent of cavitation. Acoustic data from vortex based cavitation devices for a range of operating pressure drop (0 – 390 kPa) was obtained. Systematic methodology for identifying relevant acoustic features is presented. ‘Audio’ and ‘DSP’ Toolboxes of MATLAB were used for processing acoustic data. Three specific trends of extracted features with respect to flow rate/ pressure drop across HC device were observed. All the three trends clearly identified inception of cavitation between 50 to 80 kPa pressure drop across the HC device. An attempt is made to connect features extracted from acoustic signals with the extent of cavitation in terms of per-pass performance of HC device. The ‘flatness’ was found to capture influence of HC device scale on performance (in other words, extent of cavitation) reasonably well. The methodology is quite general and will be applicable for any cavitation device. The presented results will be useful for on-line identification of inception and extent of hydrodynamic cavitation.