Studies On Drag Force Of Aggregate Particles And Wake Effect In Acoustic Agglomeration Processes

In China,the problem of fog and haze has always been the focus of environmental protection,mainly caused by industrial emission of respirable particulate matter,including PM₁₀ and PM_2.5.The conventional dust removal equipment used in the industry has low efficiency in removing respirable particulate matter.But the pretreatment can improve the dust removal effect,and the sonic agglomeration technology is a promising pretreatment technology.The force of fine particles in the sound field is mainly the airflow’s drag force,and the wake effect is an important mechanism of sound agglomeration.In view of this,the drag force and the mechanism of wake effect of fine particles is studied.In this paper,a test bench for measuring the particles’drag force by the falling ball method was built,and the glass particles were used to simulate the aerosol particles’sedimentation,thereby obtaining the particles’drag correction coefficient.For fluids,viscous glycerin was used in this research.The CFD（Computational Fluid Dynamics）software was used to simulate the drag force and wake effects of fine particles.First,the effects of some dimensionless coefficients on the drag correction coefficient are studied.Experimental results show that the drag correction coefficient of the agglomerates increases linearly with the increase of the particle size ratio.For rectangular agglomerates,the drag correction coefficient is inversely proportional to the aspect ratio.Experiments on some special shape agglomerates show that the drag correction coefficient increases with the increase of the angle of the agglomerate itself.In addition,as the angle between the agglomerate and flow field increases,the drag correction coefficient increases linearly.The particle number of the agglomerate has a linear positive correlation with the drag correction coefficient,and the agglomerate dispersion is inversely proportional to the drag correction coefficient.For irregular agglomerates,the drag correction coefficient is gradually smaller as the fractal dimension of the agglomerates increases.Then,numerical simulations are performed on the wake effect.The results show that when the angle between the particle and the sound field is 0°³0°,the particles attract each other.As the distance between the particles decreases,the polymerization speed first increases and then decreases,while the 0°working time is shorter than30°.When the angle between the particle and the sound field is 60°⁹0°,the particles repel each other,and the particle polymerization speed decreases with the increase of the distance.When the distance between particles is as large as 100μm,the decreasing tendency begins to be gentle.The larger the angle between the particles and the sound field,the faster the particles repel each other.In addition,the effects of acoustic frequency and acoustic vibration velocity on the wake effect are studied.When the amplitude of the acoustic vibration velocity is the same,the higher the acoustic frequency,the greater the polymerization speed.Similarly,when the acoustic frequency is the same,the larger the amplitude of the acoustic vibration velocity,the faster the polymerization speed.