Intensification of mixing in an ultrasonic flow reactor

Abstract

The aim of the project including this study is to provide a methodology facilitating the scaling up of ultrasonic flow reactors. To achieve this goal, the philosophy consists in developing lab size ultrasonic flow reactors, in which chemical process could be developed, stackable in parallel to reach industrial production volumes. The first step of this research project is to characterize the flow and the mixing within the 30 kHz vibrating walls of a millimetric-sized channel prototype specifically developed for this project. Mixing performances of this channel are measured by imaging the mixing between distilled water and brilliant blue dye solution thanks to a camera. Images grey scale levels are linked to concentration field of brilliant blue in water thanks to a calibration. Tests are done with and without ultrasonic waves for Reynolds number ranging from 5.2 to 130.6 and electrical power of the ultrasonic transducers ranging from 4 to 64 W. The study has shown mixing enhancement thanks to ultrasound. The mixing quality decreases as flow rate increases while asymptotically increases as the electrical power increase. The optimal electrical power divided by the flow rate has been found equal to 260 J/ml for the best reached mixing efficiency equal to 0.9 (maximum theoretical mixing efficiency is 1).