Combined effects of flow, surface stabilisation and salt concentration in aqueous solution to control and enhance sonoluminescence

Sonoluminescence (SL) intensity can be increased with potassium iodide (KI) concentration, attributed to a reduction in the gas concentration of solution. However, bubble properties and active bubble distributions at different frequencies and powers also influence SL intensities. Hence, to elucidate how salt concentration affects SL intensity, a systematic study with parametric variation was undertaken. SL from KI solutions of 0.1, 1 and 2 M concentration, without flow and in the presence of flow at 24, 228 and 626 mL/min was investigated at 44, 300 and 1000 kHz. At all frequencies an increase in KI concentration caused a change in the active SL distributions. For 44 kHz, localised and standing wave field SL activity could be expanded. Flow at this frequency augmented SL and SL was maximised at the lowest power setting under stabilisation at the highest KI concentration. At 300 and 1000 kHz, attenuation of the sound field was reduced, allowing expansion of activity throughout solution. In this instance, augmentation of SL intensity was only observed under flow conditions at concentrations of 1 M (300 kHz) and 2 M (1000 kHz) under stabilisation. It was theorised that a combination of smaller bubbles at higher KI concentrations and flow effects could reduce bubble clustering and enhance field formations. This was most prevalent where the standing wave was reinforced under stabilised (44 and 300 kHz) or flow (1000 kHz) conditions, here the number of active bubbles in high pressure regions likely increases. Lastly, it was found that in KI solutions flow could localise SL activity beneath and at the flow inlet via reflection and aeration mechanisms.