Theoretical estimation of the temperature and pressure within collapsing acoustical bubbles
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Date
2014
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Formation of highly reactive species such as OH, H , HO2
and H2O2 due to transient collapse of cavitation
bubbles is the primary mechanism of sonochemical reaction. The crucial parameters influencing the formation
of radicals are the temperature and pressure achieved in the bubble during the strong collapse.
Experimental determinations estimated a temperature of about 5000 K and pressure of several hundreds
of MPa within the collapsing bubble. In this theoretical investigation, computer simulations of chemical
reactions occurring in an O2-bubble oscillating in water irradiated by an ultrasonic wave have been performed
for diverse combinations of various parameters such as ultrasound frequency (20–1000 kHz),
acoustic amplitude (up to 0.3 MPa), static pressure (0.03–0.3 MPa) and liquid temperature (283–
333 K). The aim of this series of computations is to correlate the production of OH radicals to the temperature
and pressure achieved in the bubble during the strong collapse. The employed model combines
the dynamic of bubble collapse in acoustical field with the chemical kinetics of single bubble. The results
of the numerical simulations revealed that the main oxidant created in an O2 bubble is OH radical. The
computer simulations clearly showed the existence of an optimum bubble temperature of about
5200 ± 200 K and pressure of about 250 ± 20 MPa. The predicted value of the bubble temperature for
the production of OH radicals is in excellent agreement with that furnished by the experiments. The existence
of an optimum bubble temperature and pressure in collapsing bubbles results from the competitions
between the reactions of production and those of consumption of OH radicals at high temperatures.
Description
Keywords
Cavitation bubbles, Sonochemical reaction, Computer simulations, OH radical, Bubble temperature