Particle Segregation Research Articles

Characteristics of particulate matter during New Year's eve fireworks and Taal volcano ashfall in Metro Manila on January 2020

In this study, we describe the chemical and physical characteristics of two air pollution events in the first half of January 2020 in Metro Manila, Philippines, namely the New Year's eve fireworks and the Taal volcano ashfall. During the New Year's eve fireworks, PM2.5 concentration and most of the chemical components increased three-fold. However, we found disproportionately higher increases for certain metallic components typically used as pyrotechnic propellant and/or colorant for blue, white, and green light: Fe(5-fold), Cr(5-fold), Cu(8-fold), Ni(9-fold), V(10-fold), Ti(11-fold), and Ba(34-fold). These results provide insights for health assessments and legislation related to fireworks emissions. On January 12, 2020, the Taal volcano eruption caused much concern in Metro Manila as visible tephra deposits were observed. There was only a slight increase (8%) in PM2.5 concentration and its components related to basaltic ash. The low PM2.5 concentration was mainly due to the inhibited intrusion of ash into the stable nocturnal boundary layer. In addition, the detection of lightning in the plume and umbrella region showed size segregation of ash particles. The WRF-Chem model was able to capture the distribution of both tephra advection and fallout, a first for Taal volcano, making it possible for use in the future ashfall forecasting.

A force partitioning method to model spherical particles in liquid flows with low grid resolution

We have extended the traditional point-force method for modeling suspended small particles to include a force partitioning approach for particles that are slightly larger than the grid size. This size range falls between the limits of applicability for both the point-force and immersed-boundary methods. In our approach, we partition the modified term of the momentum exchange between the solid and fluid phases into the grid cells based on the area and volume fraction of the solid particle contained in each cell. We demonstrate that, for particle Reynolds numbers less than 40 and using the relatively coarse grid resolution, our method yields resolution-consistent results for the flow field, which are in good agreement with those obtained using the highly resolved immersed boundary method. By incorporating our method with the immersed-boundary method to handle large-sized particles, we demonstrate the ability to efficiently model the segregation of mixed-sized particles in liquid flows.

Particle size and shape effect of Crumbler® rotary shear-milled granular woody biomass on the performance of Acrison® screw feeder: A computational and experimental investigation

Physical experiments and discrete element model (DEM) simulations are conducted to evaluate particle characteristics and operation parameter effects on screw feeding performance for rotary shear-milled Douglas fir. Three performance metrics are used: mass flow rate, shaft driving torque, and specific energy consumption. The impact of particle size, particle size distribution (PSD), shaft rotational speed (rpm), and hopper dimensions on the performance are investigated. All employed performance metrics reveal the superior flowability of the 2-mm particles in contrast to the larger 6-mm counterpart. Remarkably, wider PSD results in poorer flowability than the two mono-sized particles, proving the flowability enhancement achieved by narrower PSD of the woody feedstock. More importantly, DEM simulations unveil PSD-induced degradation in flowability is attributed to mechanical interlocking and particle segregation effects. Furthermore, higher shaft rpm causes higher mass flow rate at the cost of higher specific energy consumption due to viscous dissipation and changes in flow pattern.

Liquefaction Behavior of a Well-Graded Gravelly Soil under Initial Static Shear Stress in Cyclic Triaxial and Simple Shear Conditions

Among other reasons, studies of the liquefaction potential of gravelly soils are limited because of the difficulties involved in preparing uniform specimens, without particle segregation, especially for a well-graded gravelly soil in a dry state for simple shear testing. Errors and difficulties are also involved in compensating for membrane penetration to a gravelly soil specimen in triaxial testing to get reliable data. Thus, innovative approaches for preparing triaxial and simple shear specimens for gravelly soils are introduced and implemented in this study to overcome experimental problems in acquiring accurate test results. In addition to the aim of obtaining reliable testing data on the liquefaction of gravelly soils under initial static shear stress for simulating sloping ground conditions, a study of the effect of various stress paths on the liquefaction resistance of gravelly soils was another goal of this research. In this regard, two sets of cyclic tests using medium-size triaxial and simple shear devices are conducted on a unique soil to compare the liquefaction potential of the tested gravelly soil using these two devices. Results of simple shear tests indicate that as the value of initial static shear stress increases, the cyclic resistance of the tested gravelly soil decreases. However, the results of the triaxial tests show that the variation of cyclic resistance for the tested soil depends on the initial static shear stress level and associated stress reversal conditions. Furthermore, the observed value of the pore water pressure ratio at failure using the strain-based liquefaction criteria for the tested gravelly soil was about 0.85, regardless of the type of testing. In addition, the relationship between the liquefaction resistance of gravelly soils using cyclic triaxial and simple shear devices was obtained.

Study on Segregation and Heat Transfer of Polydisperse Particles in a Three-Dimensional Rotating Drum by Using the DEM

The segregation and heat transfer of polydisperse particles in the rotating drum have an important impact on many industrial fields, and the theory is not completely clear. Based on the verified discrete element method model, the segregation and heat transfer of polydisperse particles in the rotating drum indirectly heated by the side wall are studied. The results show that the polydisperse particles form the segregation structure of the radial core and axial band in the rolling regime rotating drum. The comparison with monodisperse particles indicates that the heat transfer of polydisperse particles is influenced by the segregation structure. Small changes in rotation speed and filling level in the rolling regime do not alter the particle segregation and heat transfer structure. The addition of lifters is an effective means to reduce particle segregation and improve the heat transfer effect. This work provides a reference for revealing the segregation and heat transfer theory of polydisperse particles in the rotating drum.

The segregation of cement clinker particles in a mill-feeding hopper: PIV experiment and FEM modelling

The feeding hopper is frequently used in grinding cement clinker to ensure a stable and homogeneous feed of particles. However, due to the large variances in size, the clinker particles can segregate significantly and cause undesirable fluctuations in the subsequent grinding process. This work investigates the flow and segregation of particles in mill-feeding hoppers using the experimental PIV technique and the FEM simulation. The results demonstrate the different zones of fine and coarse particles, corresponding to the flow patterns of the hopper, are affected by the material parameters. Particularly, it is found that the geometric design of the hopper also has a great influence on the flow and segregation. An optimized hopper design using FEM is shown to effectively alleviate the segregation problem in the mill feeding hopper.

Secondary Motion of Non-Spherical Particles in Gas Solid Flows

Objective of this study is to investigate the effect of secondary motion of particles in multiphase gas-solid flows parametrically and test the relative impacts of particle shape and orientation information on particle distribution. For that purpose, predictive accuracies of simplified drag coefficient models are assessed for the conditions relevant to a wood recovery plant operating at dilute flow regime. After demonstrating the strong impact of the shape and orientation information on the force balance for single particles, we compared the steady state Eulerian-Lagrangian simulation results for particle volume fractions, residence times and particle diameter distributions within the chamber for different (i) superficial gas velocities (5 m/s, 7.5 m/s), (ii) orientation tendencies and (iii) particle shapes. Transient simulations are performed until the system reaches steady state conditions by monitoring the mass flow rates of the particulate phases leaving the chamber. The secondary motion of non-spherical particles is represented by stochastic sampling from the available experimental data. Analysis of the force balance on single particles revealed log-scale variations if the orientation of the particles with respect to flow fluctuates. Variations in the single particle force balances are found to be still visible in the CFD analysis, where the secondary motion of particles drastically changed the particle distribution in the chamber. The native non-spherical model which only accounts for the shape correction was found to over-predict the entrainment, leading to a significantly different particle volume fraction and diameter distributions. Spherical particle assumption also caused significant errors in the particle distribution, which increases as aspect ratio of the cylindrical particle diverges from one. Results show that particle orientation statistics are extremely important to capture the particle mixing and segregation patterns at dilute regime, which cannot be captured with such simplifying assumptions.

Particle size distribution of growing media constituents using dynamic image analysis: Parametrization and comparison to sieving

AbstractGrowing media constituents have heterogeneous particle size and shape, and their physical properties are partly related to them. Particle size distribution is usually analyzed through sieving process, segregating the particles by their width. However, sieving techniques are best describing more granular shapes and are not as reliable for materials exhibiting large varieties of shapes, like growing media constituents. A dynamic image analysis has been conducted for a multidimensional characterization of particle size distribution of several growing media constituents (white and black peats, pine bark, coir, wood fiber, and perlite), from particles that were segregated and dispersed in water. Diameters describing individual particle width and length were analyzed, then compared to particle size distribution obtained by dry and wet sieving methods. This work suggests the relevance of two parameters, FeretMAXand ChordMINdiameters for assessing particle length and width, respectively. They largely varied among the growing media constituents, confirming their non‐spherical (i.e., elongated) shapes, demonstrating the advantages of using dynamic image analysis tools over traditional sieving methods. Furthermore, large differences in particle size distribution were also observed between dynamic image analysis and sieving procedures, with a finer distribution for dynamic image analysis. The discrepancies observed between methodologies were discussed (particle segregation, distribution weighing, etc.), while describing in details methodological limitations of dynamic image analysis.

Photoactive and Intrinsically Fuel Sensing Metal-Organic Framework Motors for Tailoring Collective Behaviors of Active-Passive Colloids.

Microorganisms display nonequilibrium predator-prey behaviors, such as chasing-escaping and schooling via chemotactic interactions. Even though artificial systems have revealed such biomimetic behaviors, switching between them by control over chemotactic interactions is rare. Here, a spindle-like iron-based metal-organic framework (MOF) colloidal motor which self-propels in glucose and H2 O2 , triggered by UV light is reported. These motors display intrinsic UV light-triggered fuel-dependent chemotactic interactions, which are used to tailor the collective dynamics of active-passive colloidal mixtures. In particular, the mixtures of active MOF motors with passive colloids exhibit distinctive "chasing-escaping" or "schooling" behaviors, depending on glucose or hydrogen peroxide being used as the fuel. The transition in the collective behaviors is attributed to an alteration in the sign of ionic diffusiophoretic interactions, resulting from a change in the ionic clouds produced. This study offers a new strategy on tuning the communication between active and passive colloids, which holds substantial potentials for fundamental research in active matter and practical applications in cargo delivery, chemical sensing, and particle segregation.

3D printing of customised particles for powder rheology, mixing and segregation study

Due to the heterogeneity of particle shape and surface, it remains a big challenge for quantitative analysis of the detrimental influencing factors for certain powder kinematics. The current study aims to investigate the relative effect of particle shape and surface on the bulk properties by printing of specific particle shapes with distinct surface textures using Binder Jetting. The FT4 powder rheometer is used to analyse the powder bulk behaviour and as a blending rig for binary particle mixing and segregation study. It is found that both particle shape and surface have significant effects on the powder flow and compressibility. Specifically, surface has overcome shape effect on the flowability of irregular-shaped particles and compressibility of all particles. Different shapes exhibit different segregation behaviours when mixed with spheres. With “ideal and colourful” particles created, we anticipate in providing a strong experimental validation for simulation study of particle dynamics.

Computational particle fluid dynamics 3D simulation of the sorption-enhanced steam methane reforming process in a dual fluidized bed of bifunctional sorbent-catalyst particles

Sorption enhanced steam methane reforming (SE-SMR) is an efficient hydrogen production technology that combines steam methane reforming with CO2 capture. Reactions are shifted over their thermodynamic limits and hydrogen yield is enhanced, in more favorable thermodynamic conditions. Bifunctional sorbent-catalyst particles have been developed to assure stability over multiple cycles and to make the endothermic methane reforming and the exothermic CO2 capture completely integrated. Moreover, handling one granular material simplifies system management, reduces bed inventory and avoids the problem of segregation in case of two separated materials. The continuous and simultaneous operation of the process in a dual fluidized bed reactor (DFB), which combines a reformer and a calciner, for sorbent regeneration through high temperature calcination, increases productivity and allows a greater optimization.Aim of this work is the 3D simulation of the SE-SMR process in a DFB reactor, by the Computational Particle Fluid Dynamics (CPFD) method of the Barracuda VR® software. The simulation results in terms of solid flow, pressure balance and particles segregation are reported. A post-processing routine has been written to characterize bubbles in the two fluidized beds. The effects of bed inventory, superficial velocity and steam to methane ratio on hydrogen purity and methane conversion are discussed in the paper.

Fuel-Appropriate Distribution of the Material Layer Based on Numerical Model of Sintering with Particle Swarm Optimization Algorithm

An optimization model for the fuel distribution of the material layer with mechanism models and algorithms is presented, which can reduce the fuel ratio of ore blending and enhance the fuel content in the upper layer to improve the homogeneity of the sinter quality. The actual fuel distribution of the material layer is analyzed through the granulation model and the theoretical fuel distribution for each unit is obtained using the numerical model. Then, the fuel particle size composition and segregation characteristics are optimized via the particle swarm optimization algorithm to bring fuel distribution close to the theoretical value, with a sum of their absolute values of 0.025. In comparison with the initial conditions, the fuel particle size composition conforms to a normal distribution with increased coarse particles, and the deviation of the granules from the vertical direction of the sinter layer decreases. Through this optimization method, the sinter bed with the ideal thermal profile can be achieved, namely uniform sintering along with a reduced coke ratio.

Route of biofuel production from macadamia nut shells: effect of parameters on the particles mixing index in fluidized beds

Pyrolysis of macadamia nut shells (MNS) in a fluidized bed reactor has excellent potential to produce bio-oil. High heat transfer rates and uniform temperature in the fluidized bed can be achieved due to effective gas-solid contact in the reactor. However, binary mixtures can lead to the segregation of particles, which negatively affects heat and mass transfer in such a reactor. Therefore, a 2³ statistical experimental design was used to assess the effects of parameters (i.e., air velocity, particle diameter ratio, and mass fraction of MNS) on the mixing index of the bed of MNS and sand. Among the analyzed factors, only DMNS/DS and V/VMF influenced the mixing index (Im) within a confidence interval of 95%. Based on statistical data analysis, an air velocity 20% above the minimum fluidization and particle diameter ratio (DMNS/DS) smaller than 3 results in uniform particle mixing in the bed (i.e., reaching ideal mixing index values). Moreover, the experimental results indicate that fluidized be used for biofuel production from Macadamia nut Shells.

Effects of drying rate and slurry microstructure on the formation process of LiB cathode and electrochemical properties

The drying process of electrode slurry for LiB should be crucial to obtain higher electrochemical performance, but it has been a black box. Furthermore, the lack of sufficient information on slurry microstructure complicates solving this issue. In this study, the cathode slurries having different internal structures are prepared and characterized by rheological properties. The drying process of the coating layer is evaluated in terms of film shrinkage. When the coarse particles of active material and the network structure of acetylene-black particles are uniformly mixed, a low drying rate results in extensive particle segregation and poor cycle performance. On the other hand, it is found that insufficient dispersion of active materials causes poor rate performance. Under the optimal drying condition, the slurry microstructure is found not to affect battery performance. However, the optimization of drying conditions requires consideration of material mobility during drying.

Size-induced axial segregation of ellipsoids in a rotating drum

Granular materials of different sizes and shapes in a rotating drum tend to segregate in the axial direction. In the past, extensive numerical studies have been conducted for spherical particles, showing the phenomenon of band formation. However, the axial size-induced segregation of non-spherical particles receives limited attention. In this work, we report an interesting finding of band formation for ellipsoidal particles with aspect ratio varying from 0.5 to 2.0. The results show that for ellipsoids, two weak bands appear in the vicinity of endwalls, indicating that low flowability of ellipsoids reduces the tendency of band formation. Moreover, for different shaped particles, small particles in the bands come from different regions. The results also illustrate that the radial size-induced segregation pattern develops quickly, with small particles located at the centre and then the small particles tend to migrate along the drum to form bands.

Computational investigation of particle segregation in capsule filling for hot isostatic pressing

Particle segregation, which is defined as location-dependent congregation of particles of similar size in a powder batch, can happen during the capsule filling step of hot isostatic pressing (HIP). Segregation can lead to microstructural and macrostructural flaws of the post-HIP compact. Since a systematic study of segregation with respect to filling parameters is not reported in the literature, the current work computationally investigates the effects of the geometry of the HIP capsule, the particle size distribution of the powder batch, the vibration frequency, amplitude and duration on segregation using discrete element method simulations. The results prove that cone shaped capsules are more prone to segregation, particularly if the direction of the flow of the particles is towards the tip of the cone. Particle size distributions with larger particles are more susceptible to segregation too. Moreover, higher frequencies and amplitudes increase segregation to different extents. Vibration duration initially reduces the segregation by a small amount and then reaches to an asymptote at a characteristic duration.

Effects of laser welding parameters on the porosity and acicular phase in SiCp/6092 aluminum matrix composite welded joints

Al matrix composites (AMCs) are preferred engineering materials for aerospace and automotive industries owing to their high specific strength, superior wear resistance and low thermal expansion. It is a challenge to achieve high-quality fusion welded joints of AMCs because of the occurrence of defects such as pores, particles segregation and acicular phases. In this study, the effects of laser welding parameters including laser power, welding speed and laser incident angle on the formation of porosity and acicular phase were investigated in SiCp/6092 aluminum matrix composite welded joints using orthogonal experimental method. Range analysis of the orthogonal test results showed that the laser power and the welding speed had the greatest influence on the porosity and acicular phase size during the laser welding of aluminum matrix composites. At a heat input of 60 J/mm, the porosity in the weld was only 1.6% while that at 190 J/mm was 15.2%. Higher heat input produced a much larger size of brittle Al4C3 phases. The size of the acicular phase Al4C3 at the top and bottom of the weld was larger than that in the middle. Active Ti was added to the weld zone to mitigate the adverse effect of Al4C3 brittle phase and porosity on mechanical properties. The ultimate tensile strength increased from 115 MPa in direct laser welding to 148 MPa for the laser welding process employing the Ti interlayer. This work will provide referenceable data for designing high-quality AMC welded joints for aerospace and automotive industries.

Biaxial characterization of open-cell aluminum foams from macro to micro responses

This experimental work aimed to understand the effect of a biaxial combined compression-torsion loading complexity on the mechanical properties of two types of aluminum foams having porosities of 85% and 80% and nominal relative densities of 15% and 20%, respectively. In this investigation, open-cell aluminum foam of highly uniform architecture with a spherical porosity was designed and used to investigate the biaxial plastic response. These foams were tested under different quasi-static complex loading paths using a patented rig, called ACTP with different torsional component rates. The key responses to be examined were yield stress, stress plateau, energy absorption capacity, densification strain, micro-hardness, and microstructure. It was revealed that the greater the density of the foam with the higher the loading complexity, the greater the yield strength, the energy absorption capacity, and the micro-hardness. The highest foam strength was thus recorded under the most complicated loading path (i.e., biaxial 60°) for the densest foam (i.e., 80% porosity). This was due to the variation in the cell wall thickness. In addition, the effect of the loading complexity on the microstructure was studied using SEM. The loading complexity of biaxial-45° provides higher particle segregation at the grain boundary and a larger densification strain for the 85% porosity foams.

Hindered settling of flocculated multi-sized particle suspension, part II: Experimental study of particle segregation based on copper tailings suspension

Hindered settling of flocculated multi-sized particle suspension, part II: Experimental study of particle segregation based on copper tailings suspension

Numerical study of airborne particle dynamics in vortices near curved electrode surfaces

A study is formulated to identify unique features in the dynamical behavior of airborne particles near curved surfaces, subject to a combination of aerodynamic and electrostatic influences. Particle tracing investigation is conducted in numerically fabricated steady vortices distorted near curved electrodes. The effect of direction and strength of air circulation on uncharged airborne particles is studied relative to that of the externally induced electric field, for a range of particle sizes and inertia. Unique features such as (a) improvement, deterioration, and controlled cutoff of electrostatic capture of particles; (b) segregation of particles expelled onto the domain walls selectively based on their size and inertia; and (c) particle flight manipulation with airborne trapping in inertial limit cycle trajectories and inverse cyclonic separation are observed. These phenomena are characterized by suitably identified dimensionless numbers Stv and ξv representing the ratio of the aerodynamic drag and the dielectrophoretic force to the particle inertia, respectively.