Spatial Distribution of Acoustic Cavitation Bubbles at Different Ultrasound Frequencies

Abstract

Images of sonoluminescence, sonophotoluminescence and sonochemiluminescence are recorded in order to semi-quantitatively compare the spatial distribution of the cavitation activity at three different ultrasound frequencies (170 kHz, 440 kHz and 700 kHz) and at various acoustic amplitudes. At all ultrasound frequencies investigated, the sonochemically active cavitation zones are much larger than the cavitation zones where sonoluminescence is observed. Also, the sonochemically active bubbles are observed at relatively lower acoustic amplitudes than that required for sonoluminescence bubbles to appear. The acoustic power required for the observation of the initial cavitation bubbles increases with an increase in the ultrasound frequency. The cavitation bubbles are observed relatively uniformly throughout the reactor at 170 kHz whereas they are located away from the transducer at the higher frequencies used in this study. While these observations highlight the complexities involved in acoustic cavitation, possible reasons for the observed results are discussed.

Sono‐RAFT Polymerization in Aqueous Medium

“…Thef ormation of radicals using our ultrasonic setup was quantified via ah ydrogen peroxide (H 2 O 2 )a ssay,w here it is assumed that hydroxyl radical combination leads directly to the formation of H 2 O 2 .T he rate of H 2 O 2 formation at an ultrasonic frequency of 414 kHz initially increased with increasing power, before plateauing at moderate to high power levels ( Figure S1 in the Supporting Information), as is typical for such systems. [16] Am aximum radical generation rate was observed at an applied power of 40 W. Delivered powers were determined calorimetrically (Table S1), however,for simplicity,powers reported in the manuscript are the applied/set values.The optimum conditions (i.e.frequency f = 414 Hz, applied power P = 40 W) were selected for our investigations into the ultrasonic polymerization reaction. Fora ll experiments,t he ultrasonic reactor was jacketed with aw ater circulation system maintained at 21 8 8C, the reaction vessel was placed at ad epth of ca.…”

Sonoluminescence and sonochemiluminescence from a microreactor

“…In most cavitating systems, there exist populations of SL active and SCL active bubbles (Ashokkumar et al, 2010). These populations strongly overlap: SL active bubbles can be SCL active, and vice versa.…”

Correlation between sonochemistry and sonoluminescence at various frequencies

“…8 Our recent studies have shown that SL and SCL probe different bubble populations. 10,11 We have also reported that SL bubbles may be hotter than SCL bubbles. 12 It has been identified that the acoustic frequency and power can influence the SL and SCL bubbles in different ways.…”