Influence of ultrasound on mixing on the molecular scale for water and viscous liquids

Micromixing has a decisive action on the yield of fast reactions such as co mbustions, polymerizations, neutralizations and precipitations. The aim of this study was to test the possible effect of ultrasound on micromixing, th rough the phenomenon of acoustic cavitation. To evaluate the local state of micromixing, we used a system of parallel competing reactions involving th e Dushman reaction between iodide and iodate, coupled with a neutralization . At first, we studied the effects of the acoustic frequency on micromixing ( 20-540-1000 kHz). It was found that micromixing through acoustic cavitation and acoustic streaming was more important at 20 kHz than at 540 kHz or 1 M Hz. At high and low frequency, it was shown that the injection must be loca ted near the ultrasonic emitter. The influence of the acoustic intensity pr oved to be predominant mostly for low intensities: for an acoustic intensit y of 10 W cm(-2), a characteristic micromixing time of about 0.015 s has be en obtained. Viscous media have been studied and experiments showed that mi cromixing is more difficult to achieve than in aqueous media, but that ultr asound may be as effective as classic stirring. (C) 1999 Elsevier Science B .V. All rights reserved.