Evaluation of the Hydrodynamic Performance of High-Frequency Sonoreactors Using PIV

In this work, the influence on the flow behavior produced by different operating conditions (varying power dissipation of 300 and 450 W, that is, 60 and 90% of maximum power and two frequencies of 500 and 1000 kHz) in sonoreactors was experimentally characterized by 2D-PIV (particle image velocimetry) technique. Based on the experimental measurements performed at the different operational conditions of power and frequency, the velocity fields produced by the interaction of twelve piezoelectrics operating at the same time were obtained. The vorticity and Reynolds distribution maps at different operating conditions were also obtained. The axial circulation time (tax) was experimentally measured showing a significant decrease for higher power and frequency levels. The fastest tax obtained was 5.79 s. Energy efficiency and the specific power consumption (P/V) were also estimated at both ultrasonic frequencies and powers. Energy efficiency showed a strong dependence on specific power consumption. Distinctive recirculation patterns defined by two large lateral loops interacting with other less energetic were identified. A dimensionless number (NQP(z)) that measures the ratio between the axial flow rate (Qax(z)) and ultrasonic power (Pus) is proposed. The experimental PIV measurements showed that velocity components aligned to the acoustic streaming, prevailed over perpendicular components. Highest velocities were reached at 1000 kHz and increased with ultrasonic power. At this frequency, the highest efficient axial circulation was reached and the shorter mixing times θ95 and tax were obtained.