Evaluation of particle packing models by comparing with published test results

The existing particle packing density models each with two or more parameters accounting for certain particle interactions (the loosening effect parameter, wall effect parameter, wedging effect parameter, and compaction index, denoted by a, b, c, and K, respectively) may be classified into the 2-parameter model (with a and b incorporated), the compressible model (with a, b, and K incorporated), and the 3-parameter model (with a, b, and c incorporated). This paper evaluates these models by comparing their respective packing density predictions with the test results published in the literature. It was found that their accuracy varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, some of them become inaccurate and the errors tend to be larger at around the volumetric fractions giving maximum packing density. Relatively, the 3-parameter model is the most accurate and widely applicable.     

Effects of particle shape and packing style on ethylene oxidation reaction using particle-resolved CFD simulation

Gaining in-depth insights into the effects of particle shapes and packing style on ethylene oxidation reaction is of paramount industrial importance. In this work, reactor models of five packing structures with different particle shapes and three packing structures with different packing styles are established by employing software Blender and COMSOL Multiphysics to explore how the reaction-diffusion behaviors affect ethylene oxidation process. The reliabilities of rigid body dynamics model and particle-resolved reactor model are verified by comparing simulated and experimental pressure drops and ethylene conversions. In all the five packing structures with laminar flow conditions, the high bed porosity and low total particle surface area for the trilobe packing structure give rise to the lowest pressure drop of 27.8 Pa/m, while the internal voids cutting mode provides the excellent heat transfer capacity for the Raschig ring packing structure and the highest ethylene conversion and thereby the highest bed temperature rise of 25.1 K for the four-hole cylinder packing structure. Based on these analyses, changing the packing style to the bottom-up Raschig ring - four hole cylinder packing structure would be a good strategy for the effectively lowered reactor temperature rise by 4.8 K together with the slightly reduced ethylene conversion.     

Random packing of tetrahedral particles using the polyhedral discrete element method

The random packing of tetrahedral particles is studied by applying the discrete element method (DEM), which simulates the effects of friction, height ratio, and eccentricity. The model predictions are analyzed in terms of packing density and coordination number (CN). It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing density of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.     

Experiments on densifying packing of equal spheres by two-dimensional vibration

Densification of mono-sized sphere packings using two-dimensional （2D） vibration was experimentally studied. The effects of vibration mode, amplitude and frequency, feeding method, and container size on packing density were systematically analyzed. Useful results were obtained.     

Dense packing properties of mineral admixtures in cementitious material

The effect of ultra-fine fly ash （UFFA）, steel slag （SS） and silica fume （SF） on packing density of binary, ternary and quaternary cementitious materials was studied in this paper in terms of minimum water requirement of cement. The influence of mineral admixtures on the relative density of pastes with low water/hinder ratios was analyzed and the relationship between paste density and compressive strength of the corresponding hardened mortars was discussed. The results indicate that the incorporation of mineral admixtures can effectively improve the packing density ofcementitious materials; the increase in packing density of a composite with incorporation of two or three kinds of mineral admixtures is even more obvious than that with only one mineral admixture. Moreover, an optimal amount of mineral admixture imparts to the mixture maximum packing density. The dense packing effect of a mineral admixture can increase the packing density of the resulting cementitious material and also the density of paste with low water/binder ratio, which evidently enhances the compressive strength of the hardened mortar.     

Effect of particle polydispersity on particle concentration measurement by using laser Doppler anemometry

Measurement of particle concentration by laser Doppler anemometry (LDA) is studied on a vertical air jet seeded by a powder disperser with controlled particle and air flow rates. Particle arrival rate is utilized to retrieve particle number densities from conventional LDA operation. The effect of polydisperse nature of the particles is assessed. Comparisons between measured and estimated particle number densities suggest that only a certain portion of the particle population with a particle size to fringe spacing ratio around unity can be detected. Results indicate that reliable measurement of absolute particle concentration is possible for a particle population of narrow size distribution with an average diameter equivalent to fringe spacing. Present number density measurement technique which is useful for practical purposes with conventional LDA systems is found to yield physically reasonable profiles in both laminar and turbulent regimes.     

Improvement of boundary conditions for non-planar boundaries represented by polygons with an initial particle arrangement technique

The boundary conditions represented by polygons in moving particle semi-implicit (MPS) method (Koshizuka and Oka, Nuclear Science and Engineering, 1996 Koshizuka, S., and Y. Oka. 1996. “Moving-Particle Semi-Implicit Method for Fragmentation of Incompressible Fluid.” Nuclear Science and Engineering 123: 421–434.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) have been widely used in the industry simulations since it can simply simulate complex geometry with high efficiency. However, the inaccurate particle number density near non-planar wall boundaries dramatically affects the accuracy of simulations. In this paper, we propose an initial boundary particle arrangement technique coupled with the wall weight function method (Zhang et al. Transaction of JSCES, 2015 Zhang, T.G., S. Koshizuka, K. Shibata, K. Murotani, and E. Ishii. 2015. “Improved Wall Weight Function With Polygon Boundary in Moving Particle Semi-Implicit Method.” Transaction of JSCES. No. 20150012. [Google Scholar]) to improve the particle number density near slopes and curved surfaces with boundary conditions represented by polygons in three dimensions. Two uniform grids are utilized in the proposed technique. The grid points in the first uniform grid are used to construct boundary particles, and the second uniform grid stores the same information as in the work by Zhang et al. The wall weight functions of the grid points in the second uniform grid are calculated by newly constructed boundary particles. The wall weight functions of the fluid particles are interpolated from the values stored on the grid points in the second uniform grid. Because boundary particles are located on the polygons, complex geometries can be accurately represented. The proposed method can dramatically improve the particle number density and maintain the high efficiency. The performance of the previously proposed wall weight function (Zhang et al.) with the boundary particle arrangement technique is verified in comparison with the wall weight function without boundary particle arrangement by investigating two example geometries. The simulations of a water tank with a wedge and a complex geometry show the general applicability of the boundary particle arrangement technique to complex geometries and demonstrate its improvement of the wall weight function near the slopes and curved surfaces.