Interaction Mechanism Between Ultrasonic Cavitation And Particles

Ultrasonic cavitation plays an essential role in sonochemical reaction process. The effect of ultrasound on heterogeneous system was previously studied. Particles can affect the intensity of ultrasonic cavitation and cavitation field distribution. Simultaneously, cavitation effect could create pitting corrosion of solid surface or micro hole, thus it can cause the change of size and surface properties of porous particle. In the view of ultrasonic cavitation strengthening reaction process, we hope to get ideal sonochemical yield. On the other hand, we want to ensure the integrity of the grain to improve its reusability. Research on the interaction mechanism between them has an important guiding significance for enhancing cavitation intensity, improvement of uniformity and maintaining loading and catalytic properties of particles.Free radical is the fundamental agent of chemical reaction, whose yield indirectly reflects the intensity of cavitation field. This paper chooses the chemical reagents which are sensitive and can generate stable products with hydroxyl radicals. Then we can evaluate the strength of ultrasonic cavitation by spectroscopy analysis method. Through the experiment contrasts of methylene blue(MB) visible spectrophotometry and terephthalic acid(TA) fluorescence method, the letter is an effective measure in the heterogeneous system cavitation field. TA fluorescence method is direct-viewing, simple and feasible. The whole cavitation intensity can be obtained quickly. The powder activated carbon is selected as the typical porous particle. DMPSR, i.e., decrease in mean particle size ratio, is adopted to represent the level of particle breakage. On this basis, the effects of ultrasonic power, frequency, temperature, solid-liquid ratio, particle size, mechanical agitation and different types of particles on the cavitation intensity and particle breakage were studied. The study found that adding solid particles resulted in reducing cavitation threshold, increasing effective cavitation bubble number, facilitating mixing and mass transfer by micro jet at solid-liquid interface. Thus, the effect of solid particles constitutes three mechanisms that all lead to strengthening the intensity of cavitation and homogenizing acoustic field distribution. While adding solid particles had a suppression effect on the cavitation intensity through acoustic scattering and absorption.It was found that trends of cavitation intensity and particle breakage were consistent. Even the amplitude and average rates of variation were both same. It showed that cavitation effect induced particle breakage. Furthermore, SEM micrographs, specific surface area and pore size of solid particles before and after sonication were investigated. It revealed the mechanism of ultrasound mediated particle surface. The cavitation forces including shock wave and high-speed micro-jet induced during transient collapse of cavitation bubbles had a repeated impact the surface of solid, which resulted in mechanical effects like erosion of particle surfaces or pitting.In summary, in the testing range of device, taken into the comprehensive consideration of ultrasonic cavitation strengthening and avoiding transition pitting corrosion of particles, the appropriate parameter conditions were selected. The optimal ultrasonic power was in the range of 70-80 W, the frequency stayed 20 kHz, temperature was better at 20-40?, solid-liquid ratio fall between 0.1wt%-0.7wt%, the particle size was kept within 38-75?m and the introduction of appropriate mechanical stirring was a better choice. In addition, compared to powder activated carbon, effect of granular activated carbon and powder alumina on cavitation and their breakage were lower. Above research results can provide scientific bases for reinforcing cavitation strength in solid-liquid system, contributing to reaction process and promoting chemical industrialization.