Liquid depth effect on the acoustic generation of hydroxyl radical for large scale sonochemical reactors

Liquid depth (z) is one of the most critical factors that influence the sonochemical activity, particularly for large-scale sonoreactors. This factor is one of the missing links between lab-scale sonoreactors and industrial-scale sonoreactors. Herein, computer simulations of depth effect (z = 0-8 m) on the acoustic generation of free radicals were conducted at various parameters of frequency (355-1000 kHz), acoustic intensity at the source (In,0 = 1-5 W/cm2) and bulk liquid temperature (10-40 °C). The computations were made with and without taking into account the attenuation of the ultrasound wave to concretize the influence of this event on the overall impact of depth toward the chemical activity of imploding cavities. The production of free radicals at the collapse was found to be diminished with increasing depth up to 8 m. The ultrasound wave attenuation contributed substantially in the overall reductive event, particularly at higher z and frequency and lower intensity and liquid temperature. The overall reductive effect of depth was strongly operating conditions-dependent. It was more pronounced at higher frequency (1000 kHz) and lower acoustic intensity (1 W/cm2) and bulk liquid temperature (10 °C). Depending on cavitation conditions, the attenuation of the sound wave may suppress completely the production of free radicals at small depths. All these findings were interpreted and discussed through comparison with results of previous experimental observations. In conclusion, the present computation study may furnish important data for understanding cavitation process in big-scale sonoreactors, in which attenuation of the sound wave with depth could inhibit significantly the intensity of the sonochemical process.