Numerical Simulation On Dispersion Behavior Of RLCA Aggregates Using Discrete Element Method

Uniform mixing the nano-powder in the polymer matrix is an important method to improve the physical and mechanical properties of the composite material,but the nano-particles in the powder are very easy to form agglomerates under the action of adhesion,which seriously damages the excellent performance of the nano-scale particles.Therefore,it is of great significance to improve the dispersion uniformity and dispersion degree of aggregates in the processing flow field.The existing experimental methods are difficult to accurately observe the movement information of nanoparticles in the flow field,so it is difficult to study the dispersion mechanism of aggregates in the flow field and evaluate the dispersion effect of aggregates.At present,the research on this subject is mainly achieved by computer numerical simulation.With the development of the Discrete Element Method(DEM),some scholars have used the discrete element method to study the dispersion behavior of fractal aggregates in the flow field,but the fractal aggregates studied are usually generated using Diffusion Limited Aggregation(DLA)model or Diffusion Limited Cluster-Cluster Aggregation(DLCA)model.Therefore,these two models have some limitations.In order to improve the calculation accuracy of the dispersion behavior of cohesive particles in the flow field,the contact force and van der Waals force must be coupled when calculating the force between particles,and the influence of the velocity field on the drag force must be considered when calculating the drag force of particles in the flow field.In this paper,the Reaction Limited Cluster-Cluster Aggregation(RLCA)model is used to generate particle aggregates.The DEM is used to model the dispersion dynamics of adhesive particle aggregates,the JKR contact model is used to calculate the normal contact force between particles,and the Thornton model is used to calculate the tangential contact force between particles,Stokes' law is used to calculate the fluid drag force and the method proposed by Kim et al.is used to correct the fluid drag force of the particles to reflect the influence of the fluid velocity field.The simulation results show that the larger the bonding index and the initial bonding probability,the fewer the Brownian motion steps required to complete the RLCA fractal agglomeration process,and the smaller the fractal dimension of the generated RLCA agglomerates,and as the particle concentration increases,the fractal dimension of the generated RLCA agglomerates increases.The dispersion behavior of RLCA composed of adhesive particles in the flow field is studied.It was found that the dispersion process of RLCA agglomerates in the flow field was deformed first,and then broken,finally the weighted average particle number of the fragments no longer changed;With the increase of surface energy of adhesive particles,the weighted average number of fragments after dispersion of RLCA agglomerates increases with power-law relationship.With the increase of flow field strength,the weighted average number of fragments after dispersion of RLCA agglomerates increases with power-law relationship.Under the same intensity of flow field,the dispersion effectiveness of extensional flow is better than shear flow.