Experimental and theoretical characterisation of sonochemical cells. : Part 2: cell disruptors (Ultrasonic horns) and cavity cluster collapse

Abstract

Cavitation theory is used to predict the acoustic pressure at the boundary of the inertial/non inertial threshold for a range of bubble sizes. The sound field generated from a commonly employed sonoelectrochemical cell is modelled. The model is tested with a calibrated hydrophone far from the transducer to avoid spatial averaging. This allows the model to provide the absolute pressure amplitude as a function of axial distance from the source. An electrochemical technique for detecting both inertial and non-inertial cavitation within the solution is employed. This technique uses a dual microelectrode to map the boundary between the regions where inertial cavitation occurs (associated with surface erosion), and where it does not. This zone occurs close to the transducer for the microelectrode employed (<1.5 mm). Further characterisation of the inertial cavitation zone is achieved by imaging of multibubble sonoluminescence (MBSL). The pressures at the boundary between inertial and non inertial cavitation that are determined from the electrochemical and imaging experiments are compared to a sound field model and cavitation theory. Qualitative arguments for the invasive nature of the electrode into the sound field are proposed. Evidence for cavity cluster collapse and shock wave emission is presented and discussed in relation to luminescence, the electrochemical experiments and cavitation theory.

Prediction of far-field acoustic emissions from cavitation clouds during shock wave lithotripsy for development of a clinical device

“…These situations for bubble collapse and jet formation are likely to take place in many practical circumstances where shock waves are generated in bubble clouds (including lithotripsy, ultrasonic cleaning, etc. [13,51]) because pressure waves from the collapse and rebound of some bubbles will pass over neighbouring bubbles. Therefore, it is necessary to carry out a study to investigate how the collapses of neighbouring bubbles are affected by their mutual interactions.…”

The study of surface processes under electrochemical control in the presence of inertial cavitation

“…Further discussion of this point is beyond the scope of this paper and is reported elsewhere [14]. This implies that prior to any event that induces a re-passivation transient, the electrode is essentially shielded by the collapsing bubble.…”

“…However, modification of the apparatus allowed XY motion of the microelectrode with respect to the tip with a resolution of 10 µm. Electrochemical data was captured on a PC through an ADC card (Talismann Electronics, Computer Boards PCI-DAS 4020/12) and software written in-house [14].…”

The acoustic bubble: Oceanic bubble acoustics and ultrasonic cleaning

“…However, it would not be correct to equate the bubble activity in the cleaning bath with that which occurs in the UAS. The ultrasonic cleaning bath causes cavitation, whereby bubbles collapse under ultrasound to generate shock waves [27][28][29] and can also involute to form microjets [30,31], both of which can remove material from surfaces [32,33]. In contrast, the UAS system projects sound down a column of water [34] in order to excite surface waves [35][36][37] on the walls of microscopic bubbles on the surface to be cleaned.…”