Degree Of Particle Clustering Research Articles

Optimizing injection modes and reactor shapes in gas-particle fluidized beds using a mesoscale CFD model

We introduce the concepts of ‘multi-level-nozzle’ and ‘continuous oscillatory tapered’ fluidized beds to enhance contact efficiency and promote mixing between the gas and particle phases for a pilot-scale turbulent fluidized bed. Before delving into these concepts, we comprehensively assess the mesoscale drag correction model's parameter sensitivity, ensuring its applicability in lab-scale and pilot-scale turbulent fluidized beds, as well as pilot-scale risers. Following this evaluation, we design multiple cases to systematically investigate the influence of injection nozzle numbers, heights, and angles on the hydrodynamic mechanisms, specifically focusing on the degree of particle clustering and intermittency. Furthermore, we explore the effect of reactor shapes in terms of tapered ratios and sub-tapered bed numbers to intensify contact efficiency of two phases. By implementing these conceptual designs, we effectively enhance the intermittent extent of particles by over 30% and achieve higher oscillation frequencies with relatively low instability, leading to intensification of flow quality.

Preferential concentration of heavy particles in compressible isotropic turbulence

Numerical simulations of particle-laden compressible isotropic turbulence with Taylor Reynolds number Reλ ∼ 100 are conducted by using a high-order turbulence solver, which is based on high-order compact finite difference method in the whole flow domain and localized artificial diffusivities for discontinuities. For simplicity, only one-way coupling (i.e., the influence of fluid on particles) between the carrier flow and particles is considered. The focus is on the study of the preferential concentration of heavy particles in dissipative scale of turbulence and the underlying mechanisms. Firstly, the effect of Stokes number (St) on the particle distribution in flow of Mach 1.01 (referred to as high-Mach-number case in this study) is investigated as a necessary supplementation for the previous studies in incompressible and weakly compressible flows. It turns out that heavy particles with Stokes number close to unity exhibit the strongest preferential concentration, which is in agreement with the observation in incompressible flow. All types of heavy particles have a tendency to accumulate in high-density regions of the background flow. While all kinds of particles dominantly collect in low-vorticity regions, intermediate and large particles (St = 1 and St = 5) are also found to collect in high-vorticity regions behind the randomly formed shocklets. Secondly, the impact of turbulent Mach number (Mt) (or the compressibility) of the carrier flow on the spatial distribution of the particles with St = 1 is discussed using the simulated compressible flows with Mt being 0.22, 0.68, and 1.01, respectively. In low-Mach-number flow, particles tend to concentrate in regions of low vorticity due to the centrifuge effect of vortices and particle concentration decreases monotonically with the increasing vorticity magnitude. As Mach number increases, the degree of particle clustering is slightly weakened in low-vorticity regions but is enhanced in high-vorticity regions, which only account for a small fraction of the flow domain. This observation as well as the anomalous correlation between the fluid density and vorticity can be ascribed to the appearance of randomly distributed shocklets in high-Mach-number turbulence, which enhance the vorticity and density (pressure) immediately behind them. Finally, the effects of the forcing and cooling schemes on the properties of flow and particles are also discussed.

Elastic Property Simulation of Nano-particle Reinforced Composites

A series of numerical micro-mechanical models for two kinds of particle (cylindrical and discal particle) reinforced composites are developed to investigate the effect of microstructural parameters on the elastic properties of composites. The effects of both the degree of particle clustering and particle’s shape on the elastic mechanical properties of composites are investigated. In addition, single particle unit cell approximation is good enough for the analysis of the effect of averaged parameters when only linear elastic response is considered without considering the particle clustering in particle-reinforced composites.

Numerical characterization and modeling of particle clustering in wall-bounded vertical risers

Abstract This paper aims at investigating the capability of numerical models to accurately capture the physical characteristics of particle clustering in vertical risers. Within the energy sector, particle clustering in vertical risers of circulating fluidized bed reactors are known to play a key role in the multiphase dynamics as well as secondary processes such as catalytic conversion and heat transfer. Recent experiments suggest that particle clustering is most significant in the fully developed flow region of the riser, hence this study focuses on this region. To explore such flows, a high-fidelity large-eddy simulation framework is combined with a Lagrangian particle tracking solver to simulate statistically stationary gravity-driven risers in vertical pipes for a large range of Archimedes numbers. The walls of the reactor are modeled using a conservative immersed boundary scheme integrated with the Lagrangian particle tracking framework. A structure tracking algorithm akin to particle image velocimetry is used to accumulate statistics on individual clusters. Cluster descent velocities display excellent agreement with experimental measurements for the range of flow conditions considered. Predicted volume fraction fluctuations and mean solid concentration within the clusters also match experimental correlations. The probability distribution function of solid concentration and radial distribution function provide insight on the degree of clustering and the characteristic cluster length scale. The degree of particle clustering is found to be independent of the Archimedes number, and models for the volume fraction distribution are discussed. Statistics on the solid concentration and phase velocities for two- and three-dimensional configurations are compared, and the ramifications of simulating risers in two dimensions are discussed.

Effects of particle clustering on the tensile properties and failure mechanisms of hollow spheres filled syntactic foams: A numerical investigation by microstructure based modeling

Particle clustering originated from manufacturing process is thought to be one of the critical factors to the mechanical performance of hollow spheres filled syntactic foams. Although experimental evidence provides a qualitative understanding of the effects of particle clustering on the mechanical properties of syntactic foams, a quantitative assessment cannot be made in the absence of an appropriate micromechanical modeling strategy. In this study, three-dimensional microstructures of syntactic foams with different degrees of particle clustering were reconstructed based on random sequential adsorption (RSA) method. Three-phase finite element models considering the progressive damage behavior of the microsphere–matrix interface were accordingly developed by means of representative volume element (RVE) to quantitatively investigate the effects of particle clustering on the tensile properties and failure mechanisms of syntactic foams. The simulation results indicate that the elastic behavior of syntactic foams is insensitive to the degree of particle clustering, but the strength properties as well as the failure mechanisms are significantly influenced by the degree of particle clustering. From the micromechanical viewpoint, the clustered regions containing higher concentration of microspheres than the average volume fraction would serve as crack initiation sites due to stress concentration, and consequently lead to a negative effect on tensile strength, fracture strain, and interfacial damage of syntactic foams.

3D Finite Element Modeling for Particle-Reinforced Polymer Composites for Wind Energy Application

A series of numerical meso-mechanical models for different kinds of particle (include spherical, cylindrical and discal) reinforced composites are developed to investigate the effect of microstructural parameters on the elastic properties of composites. In these models, an effective interface concept is adopted. Finite element models with prescribed and random parameters are automatically generated in ABAQUS PDE (Python Development Environment). In the simulative investigations, it is observed that the degree of particle clustering and particle’s shape have strong effects on the elastic mechanical properties of composites.

Numerical simulation of the effect of particle spatial distribution and strength on tensile behavior of particle reinforced composites

The spatial distribution of reinforcement particles significantly influences the tensile behavior of particle reinforced composites. In this study, we have modeled the effect of particle clustering in a model metal matrix composite, SiC particle reinforced Al. The SiC particles were modeled as purely elastic, while the Al matrix was modeled as elastic–plastic. To study the effect of particle distribution, the SiC particles were represented as two-dimensional circular particles of uniform diameter. Three particle distributions – ordered, random, and clustered were evaluated. The degree of particle clustering was quantified using the coefficient of variance of the mean near-neighbor distance method. The evolution of damage by particle fracture was included in the model. The cases for (a) all SiC particles having uniform fracture strength and (b) variable fracture strength were considered (using a Weibull distribution in strength). The effects of particle distribution were elucidated and are discussed.

Microstructure-based modeling of crack growth in particle reinforced composites

Crack growth in particle reinforced composites is significantly influenced by the size, orientation, morphology and distribution of the reinforcement particles. Hence, to accurately model crack growth in such a system it is important that the complex microstructure of the particles be taken into account and not approximated by circles or ellipses. In this paper, the effects of particle morphology and distribution (homogeneous and clustered) on crack growth have been studied using the finite element method. The degree of particle clustering in aluminum/silicon carbide composites was quantified by the coefficient of variance in the mean near-neighbor particle spacing, and cluster size distributions obtained by an image analysis technique. Two-dimensional linear elastic fracture mechanics principles were used to propagate the crack, to obtain the local stress intensity values, and to gain an understanding of the local stress state. Predictions from these analyses were in agreement with experimental observations of crack growth in Al–SiC systems.

Deformation behaviour of particle-strengthened alloys: a Voronoi mesh approach

A modelling approach based on the discretisation of a particle-strengthened material using a Voronoi mesh is considered. The model is applied to studying the effects of particle arrangement on the deformation behaviour of a particle-strengthened alloy, particularly on its creep resistance. On a local scale, i.e. within an individual Voronoi cell containing a single particle, a dislocation density-based constitutive model developed previously is applied. Interaction with adjacent Voronoi cells due to plastic incompatibilities is also included. The model predicts a dependence of the creep resistance on the character of particle distribution, notably, on the degree of particle clustering. Application to oxide dispersion strengthened (ODS) nickel-base alloys MA 754 and PM 1000, which are very similar in their metallurgical characteristics, including the volume fraction of oxide dispersoids, but differ in the dispersoid arrangement, shows an excellent predictive capability of the Voronoi mesh modelling technique.

Matrix‐isolated Nano‐sized Carbon Grains as an Analog for the 217.5 Nanometer Feature Carrier

The effect of particle shape or particle clustering on the extinction behavior of nano-sized hydrogenated carbon grains is investigated experimentally. The particles were extracted by a molecular beam technique at different condensation and clustering states and isolated in an argon matrix for UV spectroscopy. The state of clustering in the samples was controlled by transmission electron microscopy analysis. The simple spherical morphology of the matrix-isolated nonagglomerated particles permitted the derivation of reliable optical constants. A clear correlation was found between the measured UV feature width and the degree of particle clustering, in agreement with theoretical investigations based on the derived optical data. Therefore, the results prove unambiguously the expectation that the optical properties of carbonaceous grain material are strongly influenced by the particle shape and the clustering degree. For particles produced in hydrogen-containing atmospheres, the UV extinction peak was shifted blueward to a position close to the 217.5 nm hump. This shift was found to be nearly independent of the amount of hydrogen in the condensation zone. We also discuss the infrared spectra of the hydrogenated carbon materials. The astrophysical implications of the results are discussed with regard to the observational as well as the elemental abundance constraints.