A novel approach to intensify fluid mixing by introducing a “pre-cavitation” stage in an ultrasonic microreactor

Generation and oscillation of cavitation bubbles are key factors to intensify fluid mixing in ultrasonic microreactors (USMRs). This work proposed a strategy of introducing a “pre-cavitation” stage in a novel USMR (I-USMR), which facilitates accelerating the cavitation and fluid mixing in the mixing zone. The cavitation phenomenon and mixing characteristics in the I-USMR were investigated. Two distinct cavitation bubble patterns, bubble array and bubble cluster, were identified and mapped using dimensionless parameters. Due to the accelerated development of cavitation, very rapid mixing was achieved in both solvent-antisolvent processes and common aqueous–aqueous mixing, under small Reynolds number ( Re < 200). The mixing rate can be improved by several fold compared to previous studies. Finally, this method was applied to synthesize mini-emulsions and PEG-PLGA nanoparticles, both of which were very sensitive to the mixing efficiency, demonstrating excellent mixing performance and great potential in these applications.