Mapping of a Stirred Ultrasonic Reactor Operated in Recirculation Mode Using a Cavitation Activity Meter and Validation Using Dye Degradation

A stirred closed-loop ultrasonic reactor operating at a constant frequency of 33 kHz was systematically mapped by measuring the local cavitation activity using a cavitation activity meter. Measurements were taken at various horizontal and vertical planes under different power levels (50, 250, and 400 W), stirring speeds (0, 200, and 400 rpm), and recirculation rates (15 and 20 mL/s). The range of cavitation intensity (cavins) varied from 10 to 410 as the power levels increased, indicating a higher cavitational activity within the reactor. Increasing the stirrer speed led to improved uniformity across the reactor, with maximum cavitational activity observed around the impeller. The average cavitation strength increased with an increase in the circulation rate. A similar investigation was conducted using Procion Golden Yellow HR dye to assess degradation at the same locations within the reactor. The dye degradation results validated the cavitation activity meter contour maps, showing similar patterns and also confirming the correspondence between the chemical and physical effects of cavitation. In instances of lower cavitation intensity, the degradation was notably minimal, especially at 50 W power. The study provides both qualitative and quantitative analyses along the horizontal and vertical planes inside the ultrasonic reactor, offering valuable insights into the distribution and intensity of cavitation under different operational conditions. The maximum cavitation zone is observed around the circumference of the stirrer and close to the transducers at much larger dimensions, enhancing reactor uniformity compared to other systems, especially the ultrasonic horn system, which exhibits a cavitation zone solely below the horn tip.