Numerical investigation on the hydrodynamics of Taylor flow in ultrasonically oscillating microreactors

Ultrasonic oscillation is an efficient solution for process intensification in microreactors but with complex mechanisms. This study presents a three-dimensional simulation of Taylor flow in a square microchannel under ultrasonic oscillation. The temporal/spatial variation of the pressure and the velocity field around the bubble was investigated. Due to the pressure pulsation parallel to the oscillation direction, the non-inertial cavitation of the bubble could be induced leading to the sub-harmonic bubble surface wave. The pressure threshold for the onset of the surface wave was predicted based on the parametric resonance theory. Owing to the surface wave, a periodic oscillation of the flow field could be found and quantified both in the liquid slug and at the liquid film of the channel corner. The oscillation frequency and intensity of the flow field were determined by the Fourier analysis, then the intensification mechanism for mass transfer/mixing in ultrasonic microreactors could be clarified.