Mixing and Residence Time Distribution in Ultrasonic Microreactors

Intensification of liquid mixing was investigated in domestic fabricated ultrasonic microreactors. Under the ultrasonic field, cavitation bubbles were generated, which undergo vigorous translational motion and surface oscillation with different modes (volume, shape oscillation, and transient collapse). These cavitation phenomena induce intensive convective mixing and reduce the mixing time from 24-32 s to 0.2-1.0 s. The mixing performance decreases with the channel size, due to the weaker cavitation activity in smaller channel. The energy efficiency is comparable to that of the conventional T-type and higher than the Y-type and Caterpillar microreactors. Residence time distribution was also measured by a stimulus-response experiment and analyzed with axial dispersion model. Axial dispersion was significantly reduced by the ultrasound-induced radial mixing, leading to the increasing of Bo number with ultrasound power. VC 2016 American Institute of Chemical Engineers AIChE J, 63: 1404-1418, 2017