The effects of ultrasound on micromixing

• Sonication can interfere with Villermaux–Dushman reaction.
• Ultrasonic energy dissipation and frequency should be included in micromixing model.
• Best micromixing was achieved with a 24 kHz probe and high power settings.
• Enhanced micromixing was achieved by both stable and transient cavitation bubbles.
• High frequencies produce best micromixing in the case of transducers when all other parameters are kept constant.

The Villermaux–Dushman reaction is a widely used technique to study micromixing efficiencies with and without sonication. This paper shows that ultrasound can interfere with this reaction by sonolysis of potassium iodide, which is excessively available in the Villermaux–Dushman solution, into triiodide ions. Some corrective actions, to minimize this interference, are proposed. Furthermore, the effect of ultrasonic frequency, power dissipation, probe tip surface area and stirring speed on micromixing were investigated. The power and frequency seem to have a significant impact on micromixing in contrast to the stirring speed and probe tip surface area. Best micromixing was observed with a 24 kHz probe and high power intensities. Experiments with different frequencies but a constant power intensity, emitter surface, stirring speed, cavitation bubble type and reactor design showed best micromixing for the highest frequency of 1135 kHz. Finally, these results were used to test the power law model of Rahimi et al. This model was not able to predict micromixing accurately and the addition of the frequency, as an additional parameter, was needed to improve the simulations.