Comparison of sonochemical and sonophysical activity under various geometric conditions in 28 kHz Double-Bath sonoreactors.

Sonochemical and sonophysical activities were investigated under various geometric conditions using 28 kHz double-bath-type sonoreactors. Sonochemical activity was quantified using KI dosimetry (triiodide ion concentration), while sonophysical activity was measured via lightweight expanded clay aggregate (LECA) desorption tests (turbidity). Thirty-five different geometric conditions were tested, comprising seven distances between the sonoreactor bottom and vessel bottom (L(2)) and five water levels (L(3)). The optimal conditions for sonochemical activity [(L(2)/L(3), unit: mm): 70/76, 90/116, 70/116, 110/146, and 70/96] and sonophysical activity [(L(2)/L(3), unit: mm): 30/78, 70/88, 150/168, 30/68, and 30/38] did not match, and no conditions showing high values in both activities were found. The presence of a thin-walled vessel did not affect ultrasound transmission. However, the presence of LECAs caused a large attenuation of ultrasound and the formation of different cavitational active zones in the vessel. This was identified as the main reason for the mismatch in optimal geometric conditions for sonochemical and sonophysical activities. The sonochemical activity could be enhanced by the presence of LECAs under conditions; however, the enhanced sonochemical activity was much lower than the five highest sonochemical activities. In addition, the movement of LECAs induced by ultrasound irradiation significantly enhanced the sonophysical activity.