Behavioral dynamics of ozone microbubbles during their shrinking and collapse stages

Currently, research on the behavioral dynamics of ozone microbubbles (OMBs) is still insufficient, which restricts in-depth studies on the oxidation mechanism of this process. In response, a shrinking stage model was built using optimized Epstein-Plesset and force equations, validated via experiments. A collapse stage model based on Keller equation considered temp changes and heat conduction. MATLAB simulations show that during the shrinking stage of OMBs, two independent factors affect the shrinking rate significantly. One is the size of OMBs, the smaller OMBs exhibit a faster shrinking rate. Another is the ozone concentration in the solution, a higher one in the solution leads to a slower shrinking rate of OMBs. Furthermore, the instantaneous rise velocity of OMBs reaches a peak within 1 ms and then decreases. Larger-sized microbubbles have a higher rise velocity, slower attenuation, shorter residence time in the solution, and their trajectories are close to vertical ascent. In the collapse stage, the internal temperature and pressure of the bubble reach 3198.83 K and 913.56 MPa respectively, while the liquid phase temperature at the interface rises to 343.75 K. The high temperature lasts only 4.6 μs, and the entire process is a quasi-adiabatic compression process involving heat conduction. During collapse, the number of ozone molecules in the microbubble drops sharply to zero, with approximately 75.7% mass transferring to the liquid phase and 24.3% decomposing during quasi-adiabatic compression to generate hydroxyl radicals (·OH). However, the concentration of ·OH is only about 6.3 × 10 −15 mol/L, which is at a negligible level. Therefore, the collapse of OMBs makes a weak contribution to the degradation of pollutants in sewage and hardly plays an effective promoting role.