R.P. Zou

Evaluation of the packing characteristics of mono-sized non-spherical particles

Abstract An experimental study has been carried out under both loose and dense random packing conditions to quantify the dependence of the packing characteristics such as porosity and packing size on particle shape. It is shown that the porosity of mono-sized particles is strongly dependent on both particle shape and packing method, and for a given packing method, the porosity-shape relation can be approximately by the proper use of the packing results of cylinders and disks. The results indicate that the equivalent packing diameter of a particle is only affected by particle shape and not sensitive to the method of evaluation including factors such as the packing method and the mixing composition. Based on the measurements, correlations have been formulated for predictive purposes. The formulated porosity-shape and packing size-shape relations are demonstrated to be useful in particle characterization and in porosity prediction of non-spherical particle mixtures.

Microdynamic analysis of particle flow in a horizontal rotating drum

The flow of particles in a horizontal rotating drum is studied based on the results generated by Distinct Element Method (DEM). The simulation conditions are comparable to those measured by means of Positron Emission Particle Tracking (PEPT), with a drum being 100 mm in diameter, 35% filled by spheres of 3 mm diameter, and rotating at a speed from 10 to 65 rpm. The simulation method is validated from its good agreement with the PEPT measurement in terms of the dynamic angle of repose and spatial velocity fields. The dependence of flow behaviour on rotation speed is then analysed based on the DEM results, aiming to establish the spatial and statistical distributions of microdynamic variables related to flow structure such as porosity and coordination number, and force structure such as particle interaction forces, relative collision velocity and collision frequency. An attempt has also been made to explain the effect of rotation speed on agglomeration based on the present findings.

On the relationship between porosity and interparticle forces

This paper presents an attempt to quantify the relationship between porosity and interparticle forces for mono-sized spheres. Two systems are considered: the packing of wet coarse spheres where the dominant interparticle force is the capillary force, and the packing of dry fine spheres where the dominant force is the van der Waals force. The interrelationships between porosity, capillary force and liquid content are first discussed based on the well-established theories and experimental observations. The resultant relationship between porosity and capillary force is then applied to the packing of fine particles to quantify the van der Waals force in a packing. A generalised relationship between porosity and interparticle forces results as an extension of this analysis. The usefulness of this relationship is finally demonstrated in depicting the fundamentals governing the relationship between porosity and particle size.

The packing of spheres in a cylindrical container: the thickness effect

An experimental investigation has been carried out to quantify the wall effect on porosity for uniform spheres packed in cylindrical containers. The results indicate that the wall effect should be composed of two components: the side wall effect and the top-bottom wall effect or the thickness effect, and the accurate determination of porosity and/or porosity-related properties should consider both of them

Dense random packings of spherocylinders

In this paper, the random packing of spherocylinders of different aspect ratios is simulated with an improved geometric based relaxation algorithm. It is shown that the packing density increases to a maximum and then decreases with the growth of aspect ratio, which is consistent with the literature results. However, the maximum packing density reaches 0.722 when the aspect ratio is 0.5, higher than those reported. The positions and orientations of the particles are demonstrated to be randomly distributed. The first three peaks in the radial distribution function g(r) may correspond to three possible local structures, and the second peak moves in the positive direction of the r-axis with the increase of aspect ratio. The coordination number results generally agree with those reported in the literature. Nevertheless, considering that a spherocylinder consists of a cylinder and two hemispherical parts, different types of contacts can be identified, including sphere–sphere, sphere–cylinder, and cylinder–cylinder contacts. The sphere–sphere contacts decrease and cylinder–cylinder contacts increase with the increase of aspect ratio. The findings are useful for a better understanding of the packing of spherocylinders.

Effect of material properties on the packing of fine particles

The packing of fine particles differs from that of coarse particles because of the strong cohesive interparticle forces. Consequently, material properties of particles have a strong effect on the packing structure of fine particles. This article presents a study of this effect by means of discrete element method. Variables considered include sliding and rolling friction coefficients related to the surface forces, and Hamaker constant and particle density related to the body forces acting on a particle. The results are analyzed in terms of porosity, mean coordination number and radial distribution function. It is shown that porosity increases with sliding and rolling friction coefficients as well as the Hamaker constant, but decreases with particle density, and coordination number and radial distribution function vary with these variables in line with porosity. The results have also been used to link the macrostructural property such as porosity to microstructural properties such as coordination number and radial distribution function. It is demonstrated that porosity can be described as a function of the force ratio between the van der Waals force and gravity force on a particle but the relationship varies with the sliding and rolling friction coefficients.

Packing of multi-sized mixtures of wet coarse spheres

The effect of water addition on the packing of multi-sized coarse spheres has been experimentally investigated under standard poured packing conditions. The results indicate that porosity is strongly affected by particle characteristics such as particle sizes and their distribution, in addition to water content. The packing features in the relationship between porosity and moisture content for wet multi-sized spheres are found to be similar to those for wet mono-sized spheres, implying that the same governing mechanisms apply. The comparison between the dry and wet packing systems confirms that there is a similarity between them, suggesting that the packing of wet particles can be predicted within the framework of a packing model developed for dry coarse particles. Future work in this direction is also discussed.

Critical states and phase diagram in the packing of uniform spheres

This paper presents a study of the structural transition of the packing of uniform spheres with a wide range of packing fractions. Several critical states are identified including the onset of local jamming, onset of global jamming and maximally random jammed (MRJ) states. With the increase of packing fraction ρ, the packing structure transforms from one-dimensional chains to two-dimensional triangles and finally three-dimensional tetrahedra, correspondingly undergoing phase changes from non-jamming to local jamming, global jamming, MRJ and finally crystal structure. There is a competition between FCC (face-centred cubic) and HCP (hexagonal closed packed) in the transition from disordered to ordered structure with the increase of ρ. HCP can transform to FCC after reaching its maximum at ρ=0.7.

Simulation study of the evolution mechanisms of clusters in a large-scale liquid Al system during rapid cooling processes

Molecular dynamics simulations have been performed for a large-scale system consisting of 400 000 atoms of liquid metal Al. To describe the complex microstructural evolutions in the liquid system during the rapid cooling processes, the tracing atom method and cluster bond-type index method have been used. It is demonstrated that the number of (12 0 12 0) icosahedral clusters, consisting of the 1551 bond type, with a higher degree of ordering, increases continuously and plays a critical and leading role in the solidifying transition. Various cluster configurations, formed by icosahedral clusters and Frank–Kasper, Bernal and defective polyhedra, produce the short-range-order regions in this amorphous system, while the atoms not taking part in forming clusters give the sparse regions possessing disorder characteristics. Large cluster configurations consisting of more than 150 atoms have been found and are shown to be formed by combining smaller clusters and to be different from those obtained by gaseous deposition and ionic spray methods.

Simulation of the packing of cohesive particles

Abstract The packing behaviour of cohesive particles differs from that of coarse, cohesionless particles. To understand the underlying fundamentals, we have conducted a series of studies by means of discrete particle simulation. The forces involved vary with packing conditions. The packing structures are characterised in terms of porosity, coordination number and radial distribution function, and the particle–particle or pore–pore connectivity is analysed with the Voronoi or Delaunay tessellation. The force structures and their link with jamming states are also discussed. Structural properties are shown to be correlated with porosity which links directly to the cohesive force acting on a particle.