Flow effects on sonochemical oxidation activity in a 20 kHz ultrasonic horn system

Abstract

Forced fluid flow, when properly aligned with the geometry of a 20 kHz horn-type sonoreactor, can increase its sonochemical efficiency (SE). We designed a flow-through reactor configuration to evaluate the effect of fluid dynamics on sonochemical activity. Using particle image velocimetry (PIV), we mapped the velocity profiles within the sonoreactor under flow rates up to 350 ml/min, and ultrasound power density from 142 to 498 W/L. KI dosimetry and sonochemiluminescence (SCL) are conducted to correlate fluid motion with chemical activity.At an ultrasound power density below 241 W/L, placing the probe near the water surface with a 288 ml/min flow rate maximized radical generation. Conversely, above 402 W/L, maximum SE is achieved with the probe near the vessel’s bottom at the same flow rate. At power densities below 241 W/L, external flow increases the liquid residence time in acoustically active zones from 0.16 to an average of 6.3 s, yielding enhanced chemical activity. Above 402 W/L, the introduction of forced flow broadens the acoustic jet, relocating bubbles from the active zone below the probe’s tip to the area around its neck. The expansion of this active zone leads to increased SE.A significant discrepancy is noted between Electron Paramagnetic Resonance (EPR) and KI dosimetry in measuring hydroxyl (OH.) radical concentrations. EPR suggests that most of these radicals are lost to recombination, highlighting the rapid dynamics of radical generation and recombination into hydrogen peroxide (H2O2) at interfacial regions.