Binary Packing of Spherical Particles with Moderate Size Ratios in Viscous Fluid: A CFD-DEM Study

Random packing of binary mixtures of spherical particles in viscous fluid is numerically investigated via CFD-DEM, where moderate size ratios (d/D) are specially considered. Results indicate that binary packing in fluid is much looser than that in the absence of fluid, and two distinct phenomena can be identified as the global packing density varies with the volume fraction of coarse particle (X_D). For small size ratios, the global packing density first increases with increasing X_D due to the occupation mechanism, and then it reaches the maximum value when X_D ≈ 0.6, beyond which the global packing density decreases as X_D increases further. However, for large size ratios, the global packing density always decreases with increasing X_D. These phenomena are further discussed by using the local packing density determined by Voronoi tessellation, the mean and local coordination number, and radial distribution function, with which the particle arrangements within binary mixtures are well identified.