The Study Of Characteristics Of Packing Of Quasi-Cylindrical Particles Based On Discrete Element Method

Particle packing widely exists in fields of geology,agriculture,medicine,material metallurgy,chemical engineering etc.In petrochemical industry,it is of great significance to study the packing characteristics of catalyst particles to optimize the heat and mass transfer in fixed bed reactors.The application of non-spherical particle packing is much wider than that of spherical particles in practice.However,the packing properties of non-spherical particle is not sufficiently studied as spheres by and large.Considering the information obtained from traditional physical experiments of particle packing is limited compared to numerical method,we established a packing model based on the Discrete Element Method for the quasi-cylindrical particle which is composed of four identical sphero-cylinders.The packing structure was studied from three indicators as packing fraction,coordination number and particle orientation.Random packing of this quasi-cylindrical particle was obtained by repeatedly filling.Influence of the initial state of filling,container diameter and particle aspect ratio on random packing was investigated.Initial state of filling greatly impact the particle orientation of the final packing structure.It also turns out that the particle has a nature of horizontal orientation in packing.A small increase in the diameter of container can significantly reduce the structure's radial packing fraction,lower the average coordination number and enhance the trend of horizontal orientation of particle.Due to the concave surface of quasi-cylindrical particle the effective packing density is not inversely proportional to the aspect ratio absolutely as assumed.The more elongated particle is the more contact particles it needs to maintain stability.The flatter the particle is,the greater tend of horizontal orientation of the particles.The influence of vibration in the vertical direction on packing also has been explored.It was found that there were two kinds of densification mechanisms.One works when the vibration intensity is small,particles show a trend of horizontal orientation producing a close packing structure of low potential energy.Another takes effect when the vibration intensity is large,particles in the packing tends to rearrange vertically generating a nematic phase of high potential energy.