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In this article, the effects of liquid properties and operating conditions on gas–liquid mass transfer under ultrasound irradiation and mechanical stirring were studied and compared. Response surface methodology (RSM) was utilized for the design of experiments and evaluation of the influence of operating parameters. The maximum value of volumetric mass transfer coefficient (kLa) was found to be 0.0714 s−1 when the ultrasonic horn was located horizontally just above the gas sparger in the tank. Ultrasonic power and the position of ultrasonic horn were found to be the most significant parameters that influence kLa. Also, three empirical correlations were developed to estimate kLa considering liquid viscosity as one of the main parameters, and their estimations were compared to those estimated using existing correlations in the literature.

This paper aims at investigating the influence of acoustic streaming induced by low-frequency (24 kHz) ultrasound irradiation on mass transfer in a two-phase system. The main objective is to discuss the possible mass transfer improvements under ultrasound irradiation. Three analyses were conducted: i) experimental analysis of mass transfer under ultrasound irradiation; ii) comparative analysis between the results of the ultrasound assisted mass transfer with that obtained from mechanically stirring; and iii) computational analysis of the systems using 3D CFD simulation. In the experimental part, the interactive effects of liquid rheological properties, ultrasound power and superficial gas velocity on mass transfer were investigated in two different sonicators. The results were then compared with that of mechanical stirring. In the computational part, the results were illustrated as a function of acoustic streaming behaviour, fluid flow pattern, gas/liquid volume fraction and turbulence in the two-phase system and finally the mass transfer coefficient was specified. It was found that additional turbulence created by ultrasound played the most important role on intensifying the mass transfer phenomena compared to that in stirred vessel. Furthermore, long residence time which depends on geometrical parameters is another key for mass transfer. The results obtained in the present study would help researchers understand the role of ultrasound as an energy source and acoustic streaming as one of the most important of ultrasound waves on intensifying gas-liquid mass transfer in a two-phase system and can be a breakthrough in the design procedure as no similar studies were found in the existing literature.

Sonochemical reactors operate based on the release of high amount of energy from ultrasonic irradiations. More application in chemical processes are being developed using these reactors. But the potential of their applications are still limited largely due to the lack of understanding about their design, operational and performance characteristics. A detail review is therefore conducted on available literature in this paper. From the review, the design features of sonochemical reactors are defined by different types, number and position of ultrasonic transducers, whereas their operational parameters are determined by ultrasonic frequency and intensity. As in the case of stirred vessel, sonochemical reactors can be also characterized for their performance based on mass transfer, mixing time and flow pattern. The review claims that sonochemical reactors have potential to be more energy efficient compared to stirred vessel if designed and operated appropriately.

Sonochemical reactors have proven to be very useful for intensification of various reaction systems. However, there is a lack of understanding in mass transfer mechanism under ultrasonication due to dependency of mass transfer on various parameters. The present work aims at investigating the effect of ultrasonic intensity on volumetric gas–liquid mass transfer coefficient, kLa, as a function of gas flow rate and temperature. Response surface methodology (RSM) coupled with central composite design (CCD) was used for design, statistical analysis and evaluation of the interaction between operational parameters. The maximum value of kLa was found to be 0.0128 s−1 in an optimum range of ultrasonic intensity between 320 and 360 W, though gas flow rate was the most influential parameter for kLa. In the next part of the study, a model was developed based on ANFIS to map the input variables to the outputs. Satisfactory agreement was observed between the ANFIS predictions and experimental data.