Insight into the impact of excluding mass transport, heat exchange and chemical reactions heat on the sonochemical bubble yield: Bubble size-dependency

Numerical simulations have been performed on a range of ambient bubble radii, in order to reveal the effect of mass transport, heat exchange and chemical reactions heat on the chemical bubble yield of single acoustic bubble. The results of each of these energy mechanisms were compared to the normal model in which all these processes (mass transport, thermal conduction, and reactions heat) are taken into account. This theoretical work was carried out for various frequencies (f: 200, 355, 515 and 1000 kHz) and different acoustic amplitudes (P-A: 1.5, 2 and 3 atm). The effect of thermal conduction was found to be of a great importance within the bubble internal energy balance, where the higher rates of production (for all acoustic amplitudes and wave frequencies) are observed for this model (without heat exchange). Similarly, the ignorance of the chemical reactions heat (model without reactions heat) shows the weight of this process into the bubble internal energy, where the yield of the main species ((OH)-O-center dot, H-center dot, O and H-2) for this model was accelerated notably compared to the complete model for the acoustic amplitudes greater than 1.5 atm (for f = 500 kHz). However, the lowest production rates were registered for the model without mass transport compared to the normal model, for the acoustic amplitudes greater than 1.5 atm (f = 500 kHz). This is observed even when the temperature inside bubble for this model is greater than those retrieved for the other models. On the other hand, it has been shown that, at the acoustic amplitude of 1.5 atm, the maximal production rates of the main species ((OH)-O-center dot, H-center dot, O and H-2) for all the adopted models appear at the same optimum ambient-bubble size (R-0 similar to 3, 2.5 and 2 mu m for, respectively, 355, 500 and 1000 kHz). For P-A = 2 and 3 atm (f = 500 kHz), the range of the maximal yield of (OH)-O-center dot radicals is observed at the range of R-0 where the production of (OH)-O-center dot, O and H-2 is the lowest, which corresponds to the bubble temperature at around 5500 K. The maximal production rate of H-center dot, O and H-2 is shifted toward the range of ambient bubble radii corresponding to the bubble temperatures greater than 5500 K. The ambient bubble radius of the maximal response (maximal production rate) is shifted toward the smaller bubble sizes when the acoustic amplitude (wave frequency is fixed) or the ultrasound frequency (acoustic power is fixed) is increased. In addition, it is observed that the increase of wave frequency or the acoustic amplitude decrease cause the range of active bubbles to be narrowed (scenario observation for the four investigated models).

Automated summary

Numerical simulations were conducted to investigate the effects of heat conduction and chemical reactions heat on the chemical bubble yield of single acoustic bubbles. It was found that thermal conduction had a significant impact on production rates, while chemical reactions heat also played a role. Mass transport had a lesser effect on bubble yield. Additionally, the acoustic amplitude and wave frequency were found to influence production rates, with the maximum yield occurring at optimal ambient bubble sizes.