Hydrodynamics and mass transfer of oscillating gas‐liquid flow in ultrasonic microreactors

Abstract

in Wiley Online Library (wileyonlinelibrary.com) Ultrasonic microreactors were used to intensify gas-liquid mass-transfer process and study the intensification mechanism. Fierce surface wave oscillation with different modes was excited on the bubble. It was found that for slug bubbles confined in smaller microchannel, surface wave oscillations require more ultrasound energy to excite due to the confinement effect. Cavitation microstreaming with two toroidal vortices was observed near the oscillating bubble by a streak photography experiment. Surface wave oscillation at the gas-liquid interface increases the specific surface area, while cavitation microstreaming accelerates the interface renewal and thus improves the individual mass-transfer coefficient. With these two reasons, the overall mass-transfer coefficient was enhanced by 3-20 times under ultrasonication. As for gas-liquid flow hydrodynamics, ultrasound oscillation disturbs the bubble formation process and changes the initial bubble length and pressure drop.

Liquid–liquid two‐phase flow in ultrasonic microreactors: Cavitation, emulsification, and mass transfer enhancement

“…The introduction of acoustic field influenced the droplet formation process as well as the slug size. Figure shows that initial droplet and unit size variations in MR1 and MR0.5 are entirely different, which is in accordance with the observations in gas–liquid system . In MR1, the acoustic pressure oscillation accelerated the squeezing process, resulting in decreased droplet size.…”

“…The detailed description of the design, fabrication, and characterization of the USMR have been involved in our previous paper . The whole USMR is designed as a longitudinal half wavelength resonator with antinode plane of the highest sound intensity located at the microreactor plate .…”

“…The mechanical effect of ultrasonic irradiation can enhance mixing as well as avoid the clogging problem in microreactors . In the meanwhile, strong and uniform ultrasonic field can be realized in microreactors due to their much smaller volume in comparison with conventional reactors …”

“…In our previous work, a highly efficient ultrasonic microreactor has been built and applied to enhance miscible liquid mixing and gas–liquid mass transfer processes . Following these research, we extend the application of this reactor to immiscible liquid–liquid system.…”

Design of a High Frequency Driving Circuit of Surface Acoustic Wave Transducer

“…Some researchers have applied the SAW technologies to make SAW transducers, which the device can convert electrical energy into sound energy and convert sound energy into electrical energy. And these technical characteristics are usually applied in microfluidics community, such as acoustic microreactors[11], and microseparattors[12].…”