Global Average Hydroxyl Radical Yield throughout the Lifetime of Cavitation Bubbles

Abstract

An improved model to predict OH• yield in hydrodynamic cavitation for wastewater treatment is developed. Relaxing the chemical equilibrium assumption, the model can estimate the global average OH• yield during the whole oscillation cycle of all bubbles by considering radicals diffusion, cavitation event rate, and bubble radius distribution. Reliability of the model is verified by comparing with experimental data from literature in terms of geometric and operating parameters. The results show that the maximum OH• yield is achieved at optimal upstream pressure of 3.6 × 105 Pa, while increasing downstream pressure always enhances OH• yield. Decreasing the hole and pipe diameters benefits the OH• yield. Finally, a relevant correlation is developed for the design of cavitation reactors.

Analysis of the Influencing Factors of the Hydroxyl Radical Yield in a Hydrodynamic Cavitation Bubble of a Chitosan Solution Based on a Numerical Simulation

“…With the increase of the turbulence intensity downstream of the orifice plate, the expansion and collapse of the cavitation bubble became more severe and the decomposition rate of water vapor in the cavitation bubble accelerated. Therefore, the yield of • OH in the cavitation bubble increased when the downstream recovery pressure increased. , …”

“…To get closer to the experimental results, the following empirical formula was used to calculate the cavitation number. 20,21 C C P P…”

“…However, the cavitation number depends on the orifice discharge coefficient and the upstream and downstream pressure of the orifice plate in the actual operation of the HC equipment. To get closer to the experimental results, the following empirical formula was used to calculate the cavitation number. , where C d is the discharge coefficient under cavitation conditions, β is the ratio of the orifice diameter to the pipe diameter. When the pressure difference between P 1 and P 2 is less than 2.8 × 10 4 Pa and ( P 1 – P v )/( P 1 – P 2 ) is greater than 1.5, there will be some deviation for C d .…”

The hydroxyl radical yield prediction of cavitation bubble clouds during the hydrodynamic cavitation process for chitosan degradation

“…Based on the gas nucleus steady-state size distribution equation proposed by Commande and Prosperetti, 19,21 N ( R 0 ) represents the gas nuclei distribution function with a radius range of R ∼ ( R + d R ) per unit volume.where C i is the volume fraction of gas nuclei dissolved in water per unit volume, ξ is the average of the distribution range of the gas nuclei, λ g is the standard deviation of the actual and mean radius of the bubble, λ g = 0.002 m. 19 R 0 is the radius of the gas nucleus, which is the initial radius of the cavitation bubble, R 1 ≤ R 0 ≤ R 2 , and R 1 and R 2 refer to the minimum and maximum values of the radius distribution of the gas nuclei, respectively. The radius distribution of the gas nuclei is 20–200 μm.…”

“…The ΠOH represents the ˙OH yields of cavitation bubbles with initial radius R 0 . 18,19 ΠOH = J π( R 0 )where π( R 0 ) was the ˙OH yields of the cavitation bubble with initial radius R 0 . Eqn (25) denotes the ˙OH yields of CBC per unit volume and time.…”