Effect of ultrasonic waveforms on gas–liquid mass transfer in microreactors

This study aims to investigate the effect of ultrasonic waveforms on the gas–liquid mass transfer process. For a given load power ( P ), continuous rectangular wave yielded stronger bubble oscillation and higher mass transfer coefficient ( k L a ) than continuous triangular and sinusoidal wave. For pulsed ultrasound, the k L a decreased monotonically with decreasing duty ratio ( D ), resulting in weak enhancement at low D (≤33%). For a given average load power ( P A ), concentrating the P for a shorter period resulted in a higher k L a due to stronger cavitation behavior. For a given P A and D , decreasing the pulse period ( T ) led to an increase in k L a , which reached a constant high level when the T fell below a critical value. By optimizing the D and T , a k L a equivalent to 92% of that under continuous ultrasound was obtained under pulsed ultrasound at a D of 67%, saving 33% in power consumption.