Motion and mass transfer models for single bubble in an aluminum melt under a compound field of ultrasonic and rotating flow.

• The new coupled models were proposed to manifest the motion and mass transfer of the bubble under the compound field. • The ultrasonic frequency and acoustic pressure have little effect on the bubble trajectory, and the bubble spirals up. • The suitable ultrasonic parameters are the frequency of 50 kHz and acoustic pressure of 100 kPa. A mathematical model has been developed for single bubble motion and mass transfer for aluminum degassing under a compound field of ultrasonic and rotating flow, and it showed good agreement with experimental data. The effects of the ultrasonic frequency and acoustic pressure on the bubble size, bubble trajectory, and mass transfer rate between the bubble and melt were investigated. The ultrasonic frequency and acoustic pressure had little effect on the bubble trajectory, and its curve radius gradually increased with increasing distance. The retention time of the bubble in the compound field was much greater than that in a single rotating flow field, which is conducive for improving the purification efficiency. Under the experimental conditions of 450 rpm rotation speed and 1.1 m/s gas flow rate, the optimal parameters are a frequency of 50 kHz and an acoustic pressure of 100 kPa. [ABSTRACT FROM AUTHOR]