Segregation Of Granular Materials Research Articles

Experimental study on the combined influence of particle shape, density, and size on segregation behavior in binary and ternary granular mixtures

Segregation of granular materials is a common experience; however, a few studies consider the segregation of granular mixtures characterized by variations in particle shape. Additionally, many particle systems in industry and geophysics consist of nonspherical particles. In the present study, we conducted a series of experiments to investigate the influence of particle shape, density, and size on the dynamic characteristics and segregation behavior in binary and ternary granular mixtures. Our experimental findings demonstrated a noteworthy correlation between the final steady-state segregation intensity and the proportion of non-spherical beans and cube-shaped particles in a ternary granular mixture. Specifically, the presence of beans, which are larger than the other particles, in a binary and ternary granular mixture increased the size-induced segregation phenomenon. Conversely, the steady-state segregation intensity decreased as the proportion of cube particles, which were less dense but of the same volume as the other materials, increased in a ternary granular mixture, indicating a mitigation of density-induced segregation. The study also discusses the relationship among the dynamic angle of repose, dynamic properties, and segregation behavior arising from the effects of shape, size, and density in binary and ternary granular mixtures.

Identification of dominant DEM parameters for multi-component segregation during heap formation, hopper discharge and chute flow

Segregation of granular materials is a critical phenomenon in various industries, such as food processing, pharmaceuticals, and mining. The Discrete Element Method (DEM) is an effective tool for gaining insight into granular segregation by providing particle-level information and the freedom to model mixtures that are often difficult or impossible to achieve through experiments. To ensure realistic material behaviour and correct representation of segregation, it is essential to calibrate the model parameters systematically. However, in the context of multi-component segregation, it is extremely challenging and computationally expensive to consider all parameters in the calibration procedure since interaction parameters between components must also be considered. This work aims to identify the dominant DEM parameters for modelling multi-component segregation during hopper discharge, chute flow and heap formation in a mixture of pellet and sinter. Utilising a representative example of a multi-component mixture with different sizes, densities and shapes used in blast furnaces, the investigation is done for various initial configurations as well as various mass ratios of the mixture. Our findings revealed that, while only particle-geometry interaction parameters dominate the segregation after the hopper and chute flow, particle-particle parameters are also significant for segregation in the heap. We also demonstrated that the downstream segregation is significantly influenced by the segregation upstream. Moreover, we found that the effect of pellet-sinter interactions is negligible. This research provides insights into the dominant DEM parameters, facilitating more efficient and robust calibration of multi-component models in future research endeavours.

A review on flow and segregation of granular materials during heap formation

Segregation is an important process mainly used in industries during the flow of granular materials. A granular medium is repeatedly collected particles that have different properties like size, shape, and density. Heap formation in the industry occurs if particles with various sizes, forms, material densities or surface properties are made of bulk materials, then they spatially separate during formation of the heap. This paper provides a detailed understanding of segregation dynamics in granular flows within industrial processes. Focusing on the intricate interplay of particle characteristics, mixing phenomena, and heap formation methodology, the review delves into the essential aspects influencing the spatial separation of particles. Granular media, comprising particles with distinct properties such as size, shape, and density, undergo segregation during the flow processes commonly employed in industries. The formation of heaps becomes a consequential outcome when bulk materials consist of particles exhibiting variations in size, shape, material density, or surface properties. The comprehensive analysis within this review encompasses detailed insights into granular material flow, the intricacies of mixing, the mechanisms of segregation, and the profound effects of particle characteristics on these processes. Additionally, the paper scrutinizes various methodologies employed in industrial settings for heap formation, providing a holistic perspective on the key factors influencing segregation dynamics in granular flows. This review aims to contribute valuable insights to researchers, engineers, and practitioners involved in the optimization and control of granular material handling within diverse industrial applications.

DEM Modelling of Segregation in Granular Materials: A Review

DEM Modelling of Segregation in Granular Materials: A Review

Segregation behavior of particles with Gaussian distributions in the rotating drum with rolling regime

The mixing and segregation of granular materials are essential to provide valuable insights and references for practical industrial production. In this paper, the segregation behaviors of particles with Gaussian distributions and 40% filling level in the rotating drum with rolling regime were numerically studied by the discrete element method. The effects of rotation speed and particle size parameter λ (size ratio of the largest versus smallest particles) on the segregation behavior (mixing index, segregation rate), flow characteristics (particle velocity and trajectory, gyration degree and radius, particle size distributions) and the microscopic properties (collision, contact force, axial diffusion, and kinetic energy) of granular systems were systematically investigated. The results show that the segregation rate and degree of particles with Gaussian distributions gradually increase with the increase of the rotation speed and particle size parameter λ. The radial and axial segregation patterns become more obvious with the increase of λ. And the variation of the flow characteristics of particles with different sizes in the same system is also inconsistent. The microscopic properties of Gaussian-dispersed particles change with the rotation speed and λ. The rapid radial segregation depends on the larger pores existed in the granular system, which leads to a gradual increase of the axial dispersion coefficient of large particles and a gradual decrease of the axial dispersion coefficient of small particles.

Multiscale Brazil nut effects in bioturbated sediment

Size segregation in granular materials is a universal phenomenon popularly known as the Brazil nut effect (BNE), from the tendency of larger nuts to end on the top of a shaken container. In nature, fast granular flows bear many similarities with well-studied mixing processes. Instead, much slower phenomena, such as the accumulation of ferromanganese nodules (FN) on the seafloor, have been attributed to the BNE but remain essentially unexplained. Here we document, for the first time, the BNE on sub-millimetre particles in pelagic sediment and propose a size segregation model for the surface mixed layer of bioturbated sediments. Our model explains the size distribution of FN seeds, pointing to a uniform segregation mechanism over sizes ranging from < 1 mm to > 1 cm, which does not depend on selective ingestion by feeding organisms. In addition to explaining FN nucleation, our model has important implications for microfossil dating and the mechanism underlying sedimentary records of the Earth’s magnetic field.

Radial segregation of a gaussian-dispersed mixture of superquadric particles in a horizontal rotating drum

The mixing and segregation of granular materials are essential for industrial design and applications. In this work, the superquadric equation is used to construct spherical and non-spherical particles, and the discrete element method is used to investigate the radial segregation characteristics of a gaussian-dispersed mixture in a horizontal rotating drum. The influences of particle shape, standard deviation of the mixture, and rotating speed on the segregation behaviors are discussed by the gyration degree and mixing index. The results reveal that small and large particles are respectively distributed in the center and periphery of the drum, while the medium-sized particles are evenly distributed in the system. Larger standard deviation, smoother particle shape, and smaller rotation speed are conducive to the segregation of granular systems. When the granular system is close to the high-speed centrifugal state, the smallest particles have the largest radial velocity and are close to the drum wall.

Density and size-induced mixing and segregation in the FT4 powder rheometer: An experimental and numerical investigation

Segregation of granular materials is often induced by differences in size, density, shape and surface properties. Density and size-induced mixing and segregation of binary mixtures of glass beads and/or resin particles in the FT4 powder rheometer are investigated experimentally using a new FT4 methodology. The proposed methodology allows for quantification of mixing and segregation of components based on a mixing index. It is observed that the mixing index increases with increasing density and size ratio. Variation of flow energy and torque is related to the mixing and segregation of the mixture components, thus demonstrating that the FT4 powder rheometer may be used as a predictive tool for the tendency of mixture components to segregate under various stress conditions. Numerical analysis by DEM shows that for non-cohesive systems mixing and segregation occur by sifting of fines through interstitial gaps formed between coarse particles in the dilated region. For the non-cohesive system, higher blade tip speeds reduce the rate of mixing and minimise the segregation of different-sized components. Increasing the interfacial energy reduces the rate of mixing and alleviates the segregation of particles. For the cohesive systems, mixing occurs by rupture of cohesive fine clusters with the mixing index increasing with increasing blade tip speed owing to the higher shear stresses that break the agglomerates.

A modified calculation of particle buoyant forces in vibro-fluidized beds

Segregation of granular materials under vibration or flow conditions such as the Brazil nut effect has been well known, however, there is yet no consensus mechanisms to explain this phenomenon. This study attempts to investigate particle buoyant forces in the segregation process. To explain the difference of the segregation behavior for the large particle with different size, a modified calculation method of particle buoyant force is suggested for considering the effect of particle size ratio. A simple verification illustrates its validity.

Size segregation in compressible granular shear flows of binary particle systems

This paper deals with the modelling and simulation of segregation in granular materials. The basis is a hydrodynamic model for granular material flows, which is extended to capture the dynamic process of segregation in shear flows of systems with small and large particles. The granular flow equations consist of a set of compressible Navier–Stokes-like equations as well as an equation for the granular temperature. With the help of the granular temperature equation, the granular flow equations are able to cover a wide range of regimes, starting from dilute to arresting flows. However, this paper focuses on dry granular shear flows. It extends this hydrodynamic system in a dense shear flow regime by a segregation equation using the framework of mixture theory. Special focus is lain on the segregation direction. A procedure from mechanics is adapted to obtain the segregation direction from the granular flow system independent of the choice of the coordinate system. In particular, this is done in three-dimensional space. Due to the compressibility of the granular flow system and the structure of the derived segregation equation, solving the segregation equation requires special numerical treatment. Therefore, a suitable numerical scheme is presented which prevents the system from reaching unphysical states.

Multicomponent granular mixing in a Bohle bin Blender-Experiments and simulation.

Study of mixing and segregation of granular materials was performed in a Bohle bin blender using both computational modeling and experiments. A multicomponent mixture of pharmaceutical excipients and coated theophylline granules, an active pharmaceutical ingredient (API) was considered as the blend formulation. A DEM (Discrete Element Method) Model was developed to simulate the flow and mixing of the multicomponent blend to compare with the experimental data. DEM is a numerical modeling technique which incorporates all the material properties (such as Particle size, density, elastic modulus, yield strength, Poisson's ratio, work function etc.)to simulate granular flow (such as mixing, conveying) of particles. In simulation, the degree (Relative standard deviation) of mixing in a Bohle bin blender was assessed as a function of critical processing parameters (loading pattern, rotational rate, and fill percentage). Numerical simulation results reveal radial mixing in a Bohle bin blender is faster than axial mixing due to symmetric geometry limitation. This study investigates a numerical model-based approach to study the effect of the critical process parameters on the mixing dynamics in Bohle bin blender for a moderately cohesive pharmaceutical formulation. The DEM model can be used to provide crucial insights to developed optimized mixing protocols to ascertain the best mixing conditions for different formulation. As for example, as we try to develop a mixing protocol for another formulation with different operational parameters such as loading pattern, rotational speed, and fill percentage, one can device an optimized mixing protocol of the formulation with the help of this DEM model.

Flow &amp; Segregation of Granular Materials Out of Storage and Flowing Vessels: Application in Food Science &amp; Technology and in Bio-Pharmaceutical Engineering

Flow &amp; Segregation of Granular Materials Out of Storage and Flowing Vessels: Application in Food Science &amp; Technology and in Bio-Pharmaceutical Engineering

Segregation of granular materials in a pulsating pumping regime

The segregation of particles in a granular material is a well known effect of high importance in many industries. Concentrated suspensions like concrete are strongly influenced by the behavior of the coarse aggregates. In these suspensions, the segregation also occurs, especially during the transport of the material through pipes. Typically, concrete is pumped by using double piston pumps leading to a pulsating pumping regime in contrast to a linear (continuous) pumping. This paper shows the behavior of particles during the pulsating pumping regime and the migration in the tube axis. Discrete element simulations of dry, bidisperse materials were carried out to show the influence of material parameters and the segregation behavior. Detailed understanding of the dry material behavior is of great importance for the interpretation of characteristic phenomena, which can be also found in concentrated suspensions, like the formation of a lubrication layer during the concrete pumping.

Effect of pressure on segregation in granular shear flows.

The effect of confining pressure (overburden) on segregation of granular material is studied in discrete element method (DEM) simulations of horizontal planar shear flow. To mitigate changes to the shear rate due to the changing overburden, a linear with depth variation in the streamwise velocity component is imposed using a simple feedback scheme. Under these conditions, both the rate of segregation and the ultimate degree of segregation in size bidisperse and density bidisperse granular flows decrease with increasing overburden pressure and scale with the overburden pressure normalized by the lithostatic pressure of the particle bed. At overburdens greater than approximately 20 times the lithostatic pressure at the bottom of the bed, the density segregation rate is zero while the size segregation rate is small but nonzero, suggesting that different physical mechanisms drive the two types of segregation. The segregation rate scales close to linearly with the inertial number for both size bidisperse and density bidisperse mixtures under various flow conditions, leading to a proposed pressure dependence term for existing segregation velocity correlations. Surprisingly, particle stiffness has only a minor effect on segregation, although it significantly affects the packing density.

Investigation on Electrostatic Charging and Its Effect on Mixing of Binary Particles in a Vibrating Bed

The vibrating bed is widely applied in various industrial areas for drying, mixing, and segregation of granular materials. Triboelectrification becomes unavoidable due to frequent collisions and friction between particles and between particles and the wall, which will greatly affect the performance of the vibrating bed. In our study the triboelectrification model under the framework of the discrete element method was implemented to simulate the triboelectrification process, as well as the effect of electrostatic forces on the hydrodynamics of spherical particles and cylindrical particles. The numerical results showed that the triboelectrification could become stronger with increasing solid loading or bed diameter, and decreasing particle size. At low vibrating frequencies or amplitudes, the triboelectrification for cylindrical particles was stronger than that for spherical particles, while at high vibrating frequencies or amplitudes the triboelectrification for spherical particles became stronger. The repulsive or attractive electrostatic forces among particles could help improve the mixing between spherical particles and cylindrical particles. With the increasing vibrating frequencies and amplitudes, the mixing between spherical particles and cylindrical particles was improved and then approached a plateau. Due to strong triboelectrification between solid particles and the wall, the particles could attach to the wall due to attractive electrostatic forces from the wall, and form rings in the vibrating bed, which might deteriorate the mixing in the vibrating bed. These results may help us get insight in the triboelectrification of the vibrating bed and provide guidance in improving its performance by virtue of electrostatics.

Segregation of particulate solids: Experiments and DEM simulations

Segregation of granular materials is a complex phenomenon, difficult to measure quantitatively and to predict. Discrete element method (DEM) can be a useful tool to predict segregation effects and to support the industrial design. In this context, a very challenging idea is the characterization of the granular solids to provide the key parameters needed for a successful DEM simulation of segregation processes. Rolling friction, sliding friction and the coefficient of restitution are the critical parameters to be studied. These microscopic simulation parameters are calibrated by comparing the macroscopic behavior of granular matter in standard bulk experiments, which have the advantage of being highly repeatable and reliable.An experimental method is presented to characterize free surface segregation. The effects of different particle properties, particularly, shape and size, on segregation of cohesionless materials were investigated. From the experiments, particle size demonstrated a stronger effect on segregation than particle shape. Finally, the corresponding DEM simulations of the segregation experiments were presented. The parameters obtained by calibration were validated by the comparison of the modeled segregation behavior with the experimental results. Thus, calibrated DEM simulations are capable of predicting segregation effects.

Visualization and quantitative profiling of mixing and segregation of granules using synchrotron radiation X-ray microtomography and three dimensional reconstruction

Tomographic imaging techniques have great potential for improving understanding of the dynamics of granular materials during manufacturing, handling, and storage. In this study, the synchrotron radiation X-ray computed microtomography (SR-μCT) was used non-invasively to monitor blend homogeneity of binary mixtures. Granular samples of microcrystalline cellulose and starch were characterized using the SR-μCT individually. Simultaneously, particle distribution was investigated by calculating the frequency distribution of a statistic for testing sphericity. Then, the microcrystalline cellulose and starch granules were blended in a cylindrical container. Influences of the time of rotations TR and the time of vibration TV on the mixture homogeneity were studied with the SR-μCT and statistical evaluation. The mixing index is also adopted to evaluate the mixture homogeneity of the particle system. The results showed that mixture homogeneity is improved with increasing TR. Furthermore, segregation increased with longer TV when particles are different in size and shape. The larger starch granules of non-spherical shape have a tendency to rise to the top, while the smaller microcrystalline cellulose granules which are spherical tend to migrate to the bottom of the mixture. Therefore, we demonstrate that SR-μCT can investigate the mixing and segregation of granular materials in three-dimensions combined with statistic method.

Segregation Diagram of a Mixture of Particles with Different Sizes and Densities

Segregation in granular materials has been studied by means of Monte Carlo simulation. The mechanism of segregation in a binary mixture of particles with different sizes and densities has been investigated for shaking and rotating processes in two-dimensional space. From the simulations we have obtained the segregation diagrams for shaking and rotating. These diagrams show what type of segregation occurs in a binary mixture with given values of the size ratio and the density ratio. From the diagrams we can also know what conditions are required to avoid segregation and mix uniformly a mixture of particles with different sizes and densities by the shaking and fast rotating processes. It is also shown that in the shaking process there is a critical size-ratio above which large-sized particles always segregate upward irrespective of the density ratio. Some implications of the segregation diagrams for shaking and rotating obtained by our simulations are discussed with consideration for real granular materials.

The role of friction in mixing and segregation of granular material

We use discrete element modelling to investigate the processes of mixing and size segregation in a polydisperse mixture of spherical particles in a three-dimensional rectangular box and analyze the influence of friction between the particles on segregation. The packed bed is stirred by a rectangular bar moving periodically in the horizontal direction. The parameters were introduced to characterise the segregation and mixing intensities, and a differential equation was proposed to describe the evolution of segregation intensity approaching exponentially a certain steady state value. It was found that the dynamic friction coefficient has a non-monotonous influence on the processes of mixing and size segregation in poly-disperse granular systems. Critical value of the dynamic friction coefficient μcrit was identified. For the values of friction μ > μcrit, behaviour of granular material can be characterised as a “laminar” flow with dominating convective motion of packed bed. For values of friction μ < μcrit, behaviour of granular mattter can be characterised as “turbulent” flow with dominating “local” mixing inside the packed bed.

A dynamical systems approach to mixing and segregation of granular materials in tumblers

The physics of granular matter is one of the big questions in science. Granular matter serves as a prototype of collective systems far from equilibrium and fundamental questions remain. At the same time, an understanding of granular matter has tremendous practical importance. Among practical problems, granular mixing and its interplay with segregation is arguably at the top of the list in terms of impact. Granular mixing in three-dimensional systems is complicated, as flow induces segregation by particle size or density. Several approaches and points of view for analysis are possible in principle, ranging from continuum to discrete. Flow and segregation in three-dimensional systems is seemingly complicated; however, to a reasonable approximation, all of the dynamics takes place in a thin flowing surface layer. This observation, coupled with key experimental results, leads to a simple, compact and extensible continuum-based dynamical systems framework applicable to time-periodic flow in quasi-two-dimension...