Study Of The Electrostatic Characteristics Of Collisional Charging Of Single Particles

In the process of crushing,sieving,granulating and transportation,the particle electrification and electrostatic interactions are obvious due to the violent collision and friction between particles and between particles and walls.Highly charged particles can cause problems such as agglomeration and wall sticking,and may even cause electrical discharge,fire or explosion.Particle-to-particle and particle-to-wall collision are the main reason for particle charging in gas-solid multiphase systems.Therefore,the theories of particle-to-particle and particle-to-wall collision electrification mechanism are important to understand the electrostatics of particle systems.This paper conducts experimental research on particle charging characteristics at the particle scale,obtains the detailed mechanism of particle-particle collision charging and particle-plate collision charging and modifies the capacitor charging model.The main results of the full text are as follows:(1)A particle-to-particle collision charging experiment system was built and the reliability of the experimental system and the repeatability of the experimental data were verified to ensure the accuracy of the experimental results.The effects of particle size difference,collision speed,particle material,and particle initial charge on the charge transfer between colliding particles were explored.It reveals the internal mechanism of charge transfer during particle-particle collision.The results show that the incident particles of smaller size are positively charged after colliding with the target particles of larger size.The larger the size of the incident particles,the more charges are transferred.When different size particles collide with the target particles at the same collision velocity,the charge transfer amount per unit contact area is different due to the difference in the maximum contact area.After the same material particles with different sizes are collided and charged,the polar of charge on particles depends on the type of particle material.It also reveals the relationship between the maximum contact area during the collision and the charge transfer undergone elastic collision and plastic deformation.For POM and PA66 particles,the smaller particles are positively charged,while for PTFE particles,the smaller particles are negatively charged.The amount of charge transfer between particles generally increases with the increase of the collision speed.(2)Through theoretical analysis and finite element numerical solution,the potential difference between the contact surfaces of various materials due to the electric field of the initial surface charge is obtained.The detailed mechanism by which the initial charge of particles affects the charge transfer in the collision process is clarified.The results show that the initial charge on the particle surface limits the charge transfer between particles.The charge model of the capacitor based on the potential difference drive compares the charging tendency of particles of different materials.The order of the initial charge on particle impact charging is PTFE and POM.With PA66.The results show that the surface charge of the dielectric material will be redistributed by the polarization and cause the contact potential difference to change significantly.It is found that the essence of the initial charge of the particles on the charge transfer is the dielectric polarization of the insulator material.The relative dielectric constant of the particulate material determines the strength of the polarization between the particles,thereby changing the induced potential difference between the contact surfaces.And the higher the dielectric constant leads to the greater the induced potential difference.For two particles with different sizes that are close to each other,the smaller particle is more likely to be affected by the relative size of the two particles.This paper introduced the dielectric properties of the insulator material,put forward the corrected potential difference coefficient,and thus improved the capacitor charging model.(3)Experiments on the collision charging characteristics of particle-to-particle,particleto-wall of the same material were conducted.The influence of factors such as relative collision speed,particle size,material type,environmental humidity and plate temperature on charge transfer were investigated.The detailed rules of charge transfer during particle-plate collision are explored,and the difference between particle-particle and particle-plate collision charges is compared and analyzed.The experimental results show that the collision charge between particles of different sizes and the plate increases with the increase of the collision speed,and with the particle size,the collision charge between the particles and the plate is different,which explores the relationship between the maximum contact area and charge transfer during the collision.For hydrophilic particles,the increase in relative humidity promotes the charge transfer between the particles and the plate,while for hydrophobic particles,the increase in relative humidity leads to a decrease in the collision charge.It clarifies the internal mechanism of relative humidity affecting particle collision charge transfer.The amount of transferred charge on the particle decreases firstly and then increases with the increase of the plate temperature and the detailed law of the influence of plate temperature on impact charging was discussed.Comparing the collision charging between particles and the plate and the collision charging between particles,it is found that there are differences in the charge polarity and quantity of the collision charging.