Algerian Journal of Engineering Research
Volume 2, Numéro 4, Pages 13-20

Correlations Between The Production Of Hydroxyl Radical/hydrogen And The Maximum Temperature And Pressure Reached Inside Acoustic Bubbles

Authors : Nassim Kerabchi . Slimane Merouani . Oualid Hamdaoui .

Abstract

The chemical effects of ultrasound (sonochemistry) originate from acoustic cavitations, that is, ultrasoundinduced formation, growth and violent collapse of micro bubbles in a liquid medium. The rapid collapse of cavitation bubbles is nearly adiabatic, rendering each individual bubble a microreactor, inside which temperatures of the order of 5000 K and pressures of hundreds of atmospheres have been shown to exist. This work presents results of a comprehensive numerical assessment of chemical reactions occurring in an O2- bubble oscillating in water irradiated by an ultrasonic wave. Simulations have been performed for diverse combinations of various parameters such as ultrasound frequency (20–1000 kHz),static pressure (0.5–2 atm) and liquid temperature (20–50 °C). The aim of this series of computations was to correlate the production of HO● and hydrogen to the temperature and pressure achieved in the bubble during the strong collapse. The obtained results clearly showed the existence of an optimum bubble temperature of about 4200 °C and pressure of about 2000 atm. The predicted value of the bubble temperature for the production of HO● and hydrogen is in excellent agreement with that determined experimentally. The existence of an optimum bubble temperature and pressure in collapsing bubbles results from the competition between reactions of production and those of consumption of HO● radicals at very high temperatures.

Keywords

Sonochemistry, Acoustic cavitation, Hydroxyl radical (HO●)