The influence of ultrasound on micromixing in a semi-batch reactor

This paper deals with the micromixing phenomenon occurring when ultrasonic waves propagate in a reacting medium. Parallel competing reactions A + B -- > R and C + vB --> S were employed to quantify the micromixing. We have use d a 20 kHz horn in a batch reactor to investigate the influence of the acou stic power. Various vessels have been tested in order to study the influenc e of the reacting volume (100-500-3750 ml). The dissipated power, and not t he power per unit mass was found to be the determining variable. Then a cla ssic impeller was compared to the ultrasound device in aqueous media. Value s of characteristic micromixing time around 0.005 s have been obtained for both the mixing processes. But if ultrasound can generate micromixing, thei r energetic performances are still far lower than Rushton turbine ones. Thu s the ultrasound technique must be used in a small zone to generate locally a mixing on a small scale. Finally, the ultrasound technique was also test ed in more visquous liquids (2-170 mPa s) and proved to be of great interes t. (C) 1999 Elsevier Science Ltd. All rights reserved.