Parametrical investigation of acoustic cavitation and extraction enhancement in ultrasonic microreactors.

• Evolution process of oscillation of cavitation bubble with ultrasound was analyzed. • Acoustic cavitation was promoted at low frequency in low surface tension liquid. • A semi-experimental equation was proposed to predict the cavitation mode. • The mass transfer behavior was compared with other reactors using a power law model. • An operation guideline for ultrasound-assisted extraction process was established. Experimental studies on acoustic cavitation and ultrasound-assisted extraction process were systematically investigated in the laboratory-built ultrasonic microreactors. The cavitation evolution process of microbubble after ultrasound exposure was first analyzed, finding that surface tension plays a vital role on bubble oscillation. The effects of fluid property as well as ultrasound frequency on cavitation activity were then investigated, and a discriminating criterion was established on the basis of experimental data, which can well predict the bubble cavitation mode. In addition to acoustic cavitation, the effects of varying parameters, e.g., ultrasound frequency, input mode, on ultrasound-assisted extraction process were also investigated, the result of which, correlates well with the cavitation research from a meso-scale perspective. It was found that the overall mass transfer coefficients are solely related to the specific energy dissipation rate under all circumstances. At specific energy dissipation rate 3–675 W/kg, the overall mass transfer coefficients were measured to be 0.01–0.24 s−1, being comparable to that of reciprocating plate column and far high than the passive microreactor. [ABSTRACT FROM AUTHOR]