Simulation and experimental investigation of an ultrasound system with cavitation in concentric zone

Abstract

Nowadays, ultrasonic cavitation has been successfully used for the degradation of organic pollutants. However, many sonotrodes employed for wastewater treatment are excited to present a longitudinal vibration mode. Thus, the strongest cavitation generally occurs at the tip end of the sonotrodes or the inner walls of ultrasound baths, resulting in severe erosion of the vibrating metal surface caused by ultrasonic cavitation, even though the sonotrodes are made of titanium alloy. In addition, recontamination is possible due to corrosion of the sonotrode. To avoid the above issues, a novel ultrasound system composed of a cylindrical sonotrode and a Langevin-type transducer, is proposed for generating cavitation only in the concentric zone of the cylindrical sonotrode. The first-order longitudinal vibration and the radial vibration are simultaneously stimulated in the Langevin transducer and the cylindrical sonotrode, respectively, to produce the focused cavitation at the concentric zone of the sonotrode. At first, the finite element simulation is conducted to confirm the planned vibration of the ultrasound system and to compute its sound pressure. Subsequently, the prototype of the proposed ultrasound system is manufactured and assembled for vibration measurements. Finally, experimental investigations are carried out on the ultrasound system prototype. By the aluminum foil experiments, the cavitation bubbles occurred in the center of the cylindrical sonotrode. The erosion area increased with the increase of the working power and processing time. After treating the methyl violet solution by ultrasonic cavitation for 60 min, the methyl violet in the solution is reduced by 60%, which certainly will help the development of an appropriate flow system for dye degradation. • An ultrasound system for dye wastewater treatment without re-contamination is proposed, simulated, and experimental investigated. • Cavitation bubbles were only produced at the center of the ring sonotrode. • Concentration of methyl violet solution after ultrasonic treatment decreased significantly.