The Effect Of Ultrasonic Cavitation On Fine Particle Breakage Around Rigid Wall Under Rotating Flow Field

In the field of modern industry,traditional mechanical crushing method has a grinding limit in the process of large-scale preparation of fine particles.Agglomeration phenomenon is that the particle size cannot be decreased any longer when it is reduced to a certain extent.The liquid phase provides an effective way to reduce the fine particles agglomeration.The appropriate ultrasonic vibration in fluid phase is conducive to disperse particles and cavitation occurs.Transient high pressure occurs when cavitation bubbles collapse.The cavitation micro jet-flow with speeds up to several hundred meters per second has the eroded effect on fine particles.The cavitation micro jet-flow can accelerate the movement of the particles,causing a violent collision between the particles and between the particles and the rigid wall,resulting in further crushing of the fine particles,realizing the mechanical processing of the superfine powder.Cavitation in finer particle crushing has a significant theoretical and application value.First,theoretical research on the fine particle breakage of ultrasonic cavitation micro jet-flow near the rigid wall is carried out.Micro jet-flow decays rapidly because of the high liquid phase resistence,so the effective distance of particle broken and broken works of cavitation micro jet-flow on particles are theoretically calculated.The effect of ultrasonic frequency,ultrasonic sound pressure amplitude,liquid phase viscosity,liquid surface tension and media ball size on micro jet-flow is analyzed.The relationship between bubble collapse velocity and micro jet-flow velocity is established and analyzed.Then,numerical simulation of the motion of the ultrasonic cavitation around the rigid wall has been implemented by using software FLUENT.The influence to vapor content and turbulence kinetic energy of three factors:media ball size,liquid viscosity and power is analyzed.The simulation results show that as the media ball size and power increases,the liquid phase viscosity decreases,the cavitation area of the flow field and the turbulence kinetic energy increases,the cavitation effect is more obvious.Based on the above theoretical and simulation results,an experiment device on the influence of ultrasonic cavitation micro jet-flow near the rigid wall to crush fine particle was constructed.Ten kinds of tests under different conditions are conducted.The scanning electron microscope?SEM?technique is used to characterize the powder morphology.The distribution of the key parameters of the particle size such as median particle diameter D₅₀,10%cumulative particle diameter D₁₀ and specific surface area SSA have been analyzed.Results show that the breakage rate of fine particles below800 mesh can reach 79.35%and production rate more than 10,000 mesh can reach12.84%under below conditions:4%slurry concentration,25w power,20mm ball media size and 79168mm² of media surface area.The media ball area has a greater effect on the breakage rate than that of the power,media ball size,and the mass concentration.Finally,the dispersion characteristics of fine particles under rotating flow field by using FLUENT-EDEM coupling are simulated and experiments of ultrasonic cavitation to crush fine particles under rotating flow field are carried out.The results show that as the speed of flow field increases,the probability of collision between the particles and the media ball increases,and the breakage rate increases.This paper proposes a new particle crushing method based on cavitation impact around the rigid wall under rotating flow field.Simulation and experiment study on the effect of ultrasonic cavitation on the crushing of fine particles around the rigid wall under rotating flow field are provided and conducted.The conclusion of this research provides a significant guide for the application of cavitation impact in the industrial production of fine particle crushing.