| In order to effectively solve the problems of agglomeration and grinding limit in the preparation of fine particles by mechanical method scale,a method of preparing fine particles using a cavitating jet impact coupled with media collision is adopted.In order to explore the comminution mechanism of particle-grinding in liquid phase under cavitation impact and the effect of effective cavitation impact coupled with grinding motion on the comminution of fine particles,this paper analyzes the impact dynamics of cavitation bubble collapse on particles,at the same time,the impact process of cavitation jet near-sphere wall is simulated by FLUENT software and the relevant parameters are optimized.A cavitating jet milling test device is designed and set up,the comparative experiment of cavitating and crushing quartz sand is carried out.The theory and numerical simulation are verified,and the feasibility of the preparation method is also proved.The main contents of this paper are as follows:(1)The conditions for the effective breaking of quartz sand particles with the size of 100 micron by micro-jet and shock wave produced by cavitation collapse are analyzed,the dimensionless distance required for the effective breaking of 50-150 ?m quartz sand particles by micro-jet is 0.90-1.43,and the diameter of the quartz sand particles and the maximum radius of the critical cavities satisfy the relationship of R'max=0.2471 d 0.3864.(2)The influence of inlet pressure and target distance are discussed from the point of view of the distribution characteristics of cavitation cloud near-sphere wall.The simulation results show that the length of cavitating cloud is positively related to the inlet pressure.The optimal inlet pressure of cavitating nozzle is 5 MPa,and the optimal target distance of jet impinging on the spherical wall is 25 mm.With the increase of target distance,the volume fraction of cavitating cloud near the wall decreases gradually.(3)The orthogonal experiment of cavitating and crushing quartz sand is carried out based on multiple factors such as target distance,rotating speed rate,particle mass concentration and nozzle number,and the particle size distribution characteristics are analyzed.The experimental results show that cavitation impact coupling medium impact can rapidly reduce the particle size and increase the yield of fine particles.Cavitation impact can effectively crush particles with a particle size of 74.6-150 ?m.The crushing rate of fine particles at different experimental points has different growth rates in the same time period;the smaller the particle size,the lower the crushing rate;after 3 hours of experiment,the crushing rate of fine particles with a particle size of less than 10 ?m is as high as 67.2%.The SEM observation shows that the fine particles are well dispersed,and there are very fine particles with a diameter of about 800 nm.Target distance and rotating speed are the main factors affecting particle breakage.The best parameters are 25 mm and 60% respectively,followed by the number of nozzles.The experimental results show that cavitating jet impact coupled with medium collision has a limited crushing range for fine particles,and its applicable particle size range is slightly smaller than the theoretical calculation value,at the same time,the crushing effect of cavitating jet impinging on the ball wall under 5 MPa pressure is verified,and the optimal target distance is also corresponding to the appropriate target distance obtained by simulation.In this paper,a method of preparing fine particles using a cavitating jet impact coupled with media collision is proposed,and a cavitating jet milling test device is designed.The numerical simulation and experimental study on the effect of near-sphere wall cavitating jet on the crushing of fine particles are carried out,which provides important engineering and theoretical guidance for the application of cavitation effect in the industrial production of fine particles. |
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