Behavior Of Particles Research Articles

Motion and Combustion Behavior of Single Char Particle in Oxy-Fuel Fluidized Bed: Experimental and Modeling Studies

Motion and Combustion Behavior of Single Char Particle in Oxy-Fuel Fluidized Bed: Experimental and Modeling Studies

Bonding behavior of Ti-6Al-3Nb-2Zr-1Mo/WC composite coating on titanium alloy by gas tungsten arc welding cladding

In this study, tungsten carbide (WC) ceramic particles were introduced into the molten pool of gas tungsten arc welding (GTAW) to successfully prepare a composite coating without solidification cracking and with lower dilution. The formation mechanism and properties of the bonding interface are deeply analyzed. Results demonstrate that metallurgical bonding was achieved. The dissolution behavior of WC particles and the diffusion of W element into the heat-affected zone promoted the formation of a special β(Ti, W) diffusion layer below the fusion line. (Nb, Ti)C was mainly found distributed close to the diffusion layer. Nanoindentation test results show remarkable inhomogeneity in the interface area. The fracture surface of the broken coating revealed that the titanium matrix exhibited quasi-cleavage fracture, while the particles displayed brittle fractures. The fracture surface of coatings that experienced decohesive rupture in the shear test underwent plastic deformation in the shear direction.

Microstructure evolution and mechanical properties of selective laser melting fabricated hybrid particle reinforced AlSi10Mg composites

(SiC+TiB2)/AlSi10Mg composite powders with 5 wt% micro-SiC particles and 1.5 wt% nano-TiB2 particles were prepared by high energy ball milling, and hybrid particle reinforced aluminum matrix composites (AMCs) were fabricated by SLM. This study systematically investigated the effects of SiC and TiB2 particles on the phase composition, microstructure evolution, grain crystallization, and mechanical properties. The machanisms of potential strengthening and fracture mechanisms were revealed. The tribological behaviors of the hybrid particle reinforced AlSi10Mg composites under different friction conditions were explored as well. The results show that the 1.5 wt% nano-TiB2 particles provided sufficient nucleation sites for grain growth, completely transforming from coarse columnar to fined equiaxed grains. The average grain size decreases from 7.98 μm to 3.34 μm, and the texture is significantly weakened, which is beneficial to the homogenization of the microstructure, thereby improving the mechanical properties of the SiC/AlSi10Mg composites. The (SiC+TiB2)/AlSi10Mg composites showed a high ultimate tensile strength (∼ 489.1 MP), hardness (172.2 HV) and elongation of 8.2 %. The enhancement of mechanical properties was attributed to Orowan strengthening, fine grain strengthening, and load-bearing strengthening. Due to the Si precipitates and fine microstructure, a low wear rate of 0.50 × 10−5 g/m was obtained, 10.7 % lower than that of SLM formed SiC/AlSi10Mg composites. The friction process is affected by abrasive wear, adhesive wear and delamination wear. It is aspired that the current approach can provide guidance for the design of new alloy systems with excellent performance.

Fractal Analysis of Particle Size and Morphology in Single-Particle Breakage Based on 3D Images

The accurate modeling of single-particle breakage based on three-dimensional (3D) images is crucial for understanding the particle-level mechanics of granular materials. This study aims to propose a systematic framework incorporating single-particle breakage experiments and numerical simulations based on a novel 3D particle reconstruction technique for fractal analysis of particle size and morphology in single-particle breakage. First, the vision foundation model is used to generate accurate particles from 3D images. The numerical approach is validated by simulating the single-particle breakage test with multiple Fujian sand particles. Then, the breakage processes of reconstructed sand particles under axial compression are numerically modeled. The relationship between 3D fractal dimensions and particle size, particle crushing strength, and morphology is meticulously investigated. Furthermore, the implications of these relationships on the particle breakage processes are thoroughly discussed, shedding light on the underlying mechanisms that govern particle breakage. The framework offers an effective way to investigate the breakage behavior of single sand particles, which will enhance understanding of the mechanism of the whole particle breakage process.

Numerical modelling and experimental validation of an Enhanced multi-force model of free-fall electrostatic separators

Electrostatic separation is a crucial process for separating mixed materials, especially in recycling discarded electrical and electronic equipment. This study aims to validate an enhanced numerical model for free-fall electrostatic separators by incorporating additional forces. The model simulates particle trajectories under electrostatic forces, considering electrostatic interactions and collisions. The particles’ positions, masses, and charges are recorded to create a comprehensive database for model verification. The model was validated experimentally using three-particle mixtures of PVC-PC, PS-PC, and PS-PVC; experimental validation confirms that the updated model accurately captures the complex physical processes in the electrostatic separator. Including additional forces results in more precise particle behavior, essential for optimizing separator design and improving the purity of the separated products. The results show a concordance of mass and charge 98.812% and 96.907% for PS + PVC, 99.972% and 98.715% for PC + PVC mixtures, and 92.406% for mass and 97.244% for charge in PS+PC mixtures, demonstrating the model’s accuracy and reliability.

Structural analysis of superparamagnetic colloid aggregates confined in spherical cavities under external magnetic field

In this study, we investigated the behaviour of aggregates composed of superparamagnetic colloids under the influence of an external magnetic field, confined within several spherical cavities. The study included systems of two and three cavities in contact, as well as two cavities separated by a distance d along the direction of the external field. Monte Carlo computer simulations employing a model of hard spheres with central dipoles were realised to explore the behaviour of the magnetic particles, constrained to move within pairs (and trios) of spherical cavities. The primary focus of this investigation was to elucidate the structures formed by magnetic particles within systems presented here. Chains or ribbons primarily form within the central region of the spherical cavities. The aggregates within each cavity are drawn towards one another until they make contact at the closest points of the cavities. This behaviour is replicated when there is a separation distance between the spherical cavities, including cases where three cavities are in contact. This phenomenon may explain the observed attraction between magnetoliposomes as reported in the literature [García-Jimeno et al. Nanoscale. 9 (39), 15131–15143 (2017)].

Impact of freeze-thaw cycles on the remobilization behaviors of microplastics in natural soils

Freeze-thaw (FT) cycle would greatly influence the fate of plastic particles (one of emerging contaminants with great concerns) in soils, yet its impacts and mechanisms remain unclear. The vertical migration/release behaviors of plastic particles (with diameters of 0.2 μm and 1 μm) in two natural soils and one model soil (i.e. quartz sand) without/with FT treatments (1 and 3 cycles) were examined. Owing to the presence of Fe/Al oxide minerals, finer pore structure, and uneven surfaces of natural soils, the breakthrough ratio of plastics in two natural soils was over 25% lower than in quartz sand. However, regardless of porous media type, FT processes (increasing cycles) significantly promoted the remobilization of plastics initially retained in three media during the subsequent water flushing processes. Via theoretical calculation, tracer experiments, and visible chamber experiments, the mechanisms driving plastics release from natural soils subjected to FT treatments during the water elution processes were determined to be different from those from pure quartz sand. The change of sand local configuration (the rearrangement of local sand pore spaces) during FT process mainly drove to plastics released from quartz sand columns. While the alteration in local soil configuration, the formation of preferential pathways, and increased release of soil particles contributed to plastics remobilization from soil columns subjected to FT. Clearly, FT processes significantly increased the vertical migration of plastics in soils potentially to groundwater, enhancing environmental risks of plastics.

Kinetic study of dry magnetic separation based on Gauss-Maxwell magnetic stress tensor: A 3D finite element method (FEM)

In this paper, two artificial magnetic particles (1#, 2#) with known magnetic parameters were taken as the objects, a finite element model based on Gauss’s law was established for the calculation of the transient Maxwell magnetic stress tensor on the surfaces of particles and kinetic study, a high-speed camera was used to obtain the motion behaviors of magnetic particles in comparison with the simulation. According to the results of multiple simulation-experiment comparisons, the motion behaviors of magnetic particles in the finite element simulation were consistent with experimental phenomena under the identical conditions, indicated that the accuracy of the model is reliable. In the comparison of two kinds of magnetic force calculations, the magnetic force FM based on the Gaussian formula had a similar tendency to FD based on the kinetic calculations, and since the FM was obtained by converting the surface tension of particles, it more accurately reflected the overall magnetic force and magnetic torque acting on the particles. Kinetic analysis showed that the magnetic force acting on a particle was strictly dependent on its magnetization, dynamic and non-uniform magnetization caused the magnetic particle to be subjected to magnetic force and magnetic torque in the non-uniform magnetic field, resulting in displacements and flips. In addition, compared to the particle release attitude, the influence of the distribution of magnetic substance and the particle’s release position on the displacement was particularly significant. The 3D finite element model established for dry magnetic separation can be further used for the study of dynamic, non-uniform magnetization and the force of magnetic particle or grain groups, which is of certain significance for the kinetic study of magnetic separation and improving research of magnetic separation equipment.

Influence of Particle Size on Flotation Separation of Ilmenite and Forsterite

In addition to bubble–particle interaction, particle–particle interaction also has a significant influence on mineral flotation. Fine particles that coat the mineral surface prevent direct contact with collectors and/or air bubbles, thereby lowering flotation recovery. Calculating the particle interaction energy can help in evaluating the interaction behavior of particles. In this study, the floatability of coarse ilmenite (−151 + 74 μm) and different particle sizes (−45 + 25, −25 + 19, −19 μm) of forsterite with NaOL as a collector was investigated. The results showed that forsterite sizes of −45 + 25 and −25 + 19 μm had no effect on the ilmenite floatability, whereas −19 μm forsterite significantly reduced ilmenite floatability. A particle size analysis of artificially mixed minerals and a scanning electron microscopy (SEM) analysis of the flotation products showed that heterogeneous aggregation occurred between ilmenite and −19 μm forsterite particles. The extended DLVO (Derjaguin–Landau–Verwey–Overbeek) theory was applied to calculate the interaction energy between mineral particles using data from zeta potential and contact angle measurements. The results showed that the interaction barriers between ilmenite (−151 + 74 μm) and forsterite (−45 + 25, −25 + 19, and −19 μm) were 11.94 × 103 kT, 8.23 × 103 kT and 4.09 × 103 kT, respectively. Additionally, the interaction barrier between forsterite particles smaller than 19 μm was 0.51 × 103 kT. The strength of the barrier decreased as the size of the forsterite decreased. Therefore, fine forsterite particles and aggregated forsterite can easily overcome the energy barrier, coating the ilmenite particle surface. This explains the effect of different forsterite sizes on the floatability of ilmenite and the underlying mechanism of particle interaction.

Coupled CFD-DEM modeling of surface erosion in granular soils: Simulation of erosion function apparatus experiments

This study introduces a numerical modeling approach that couples the computational fluid dynamics (CFD) with the discrete element method (DEM) to simulate grain-scale soil erosion processes induced by water flows. In this modeling framework, CFD simulates fluid flows by solving the volume-averaged Navier-Stokes equations, and uses the k-ω turbulent model for turbulent flows. Simultaneously, DEM computes the displacement of solid particles by incorporating the fluid-particle interactions driven by fluid flows while adhering to Newton's laws of motion. These interactions encompass drag force, buoyancy force, pressure-gradient force, and viscous force exerted by fluid flows and acting on the particles. The coupled CFD-DEM modeling adeptly replicates soil erosion processes, demonstrating good alignment with results obtained from laboratory erosion function apparatus (EFA) tests. In particular, the DEM facilitates the estimation of shear stress acting on the soil surface based on fluid-particle interaction forces, which has been roughly approximated by empirical or semi-empirical models. This study underscores the capability of coupled CFD-DEM in providing valuable insights into the grain-scale behavior of soil particles subjected to fluid flows, with the potential for extension to address soil erosion and fines migration.

Initial Characteristics of Submillimeter Metal Particles in GIS under Impact Vibration

As a critical component within power systems, Gas Insulated Switchgear (GIS) is notably susceptible to insulation degradation due to submillimeter metal particles, compromising its operational safety and stability. Moreover, impact vibrations induced by circuit breaker operations can dislodge particles that typically adhere to the interior walls, causing them to become airborne and thereby intensifying their movement and discharge activities. To investigate this phenomenon, this study establishes a testing platform where alternating current (AC) voltage is superimposed with impact vibration. A camera system, interfaced with an upper computer, is used to capture the real-time motion behavior of the particles. This study focuses on characterizing the initial movement of submillimeter metal particles of varying sizes under the influence of impact vibration by analyzing critical voltages, such as the initial lift-off voltage, stable jumping voltage, and extinction voltage. Furthermore, the effects of introducing large, centimeter-scale spherical metal and rubber particles on these initial characteristics are examined. The findings provide crucial insights into the initial behavior of submillimeter metal particles in GIS, particularly in relation to circuit breaker operations.

Enhanced Diffusion and Non-Gaussian Displacements of Colloids in Quasi-2D Suspensions of Motile Bacteria

In the real world, active agents interact with surrounding passive objects, thus introducing additional degrees of complexity. The relative contributions of far-field hydrodynamic and near-field contact interactions to the anomalous diffusion of passive particles in suspensions of active swimmers remain a subject of ongoing debate. We constructed a quasi-two-dimensional microswimmer–colloid mixed system by taking advantage of Serratia marcescens’ tendency to become trapped at the air–water interface to investigate the origins of the enhanced diffusion and non-Gaussianity of the displacement distributions of passive colloidal tracers. Our findings reveal that the diffusion behavior of colloidal particles exhibits a strong dependence on bacterial density. At moderate densities, the collective dynamics of bacteria dominate the diffusion of tracer particles. In dilute bacterial suspensions, although there are multiple dynamic types present, near-field contact interactions such as collisions play a major role in the enhancement of colloidal transport and the emergence of non-Gaussian displacement distributions characterized by heavy exponential tails in short times. Despite the distinct types of microorganisms and their diverse self-propulsion mechanisms, a generality in the diffusion behavior of passive colloids and their underlying dynamics is observed.

Solidification behavior of WC particles reinforced nickel alloy cladding layers by plasma surfacing: Simulation and experiment

In this work, a numerical simulation model was developed to investigate the complex heat and mass transfer process inside the molten pool during plasma surfacing. The temperature distribution and fluid flow were employed to depict the evolution of the molten pool. The findings revealed that the maximum temperature is located on the surface of the cladding layer corresponding to the position of heat source, and the temperature distribution follows a Gaussian distribution along the scanning direction. Thermal accumulation is obvious due to the continuous energy input in the initial stage, as a result, the maximum temperature and fluid flow velocity gradually increase with the deposition process. The maximum temperature and fluid flow velocity at 4.0 s are 1893 K and 0.281 m/s in case 110 A, respectively. The predicted shapes and dimensions are consistent with the results of the deposition experiments, with a maximum error of no more than 15 %. In order to investigate the impact of WC particles on the solidification microstructure of nickel composite layers, corresponding plasma surfacing experiment was implemented. The solidification characteristics of the microstructure follow planar-cellular-columnar-equiaxed crystals in the bonding layer and WC particles-columnar-equiaxed dendritic crystals in hard layer, respectively. Furthermore, the Ni dendritic near the retained WC particles transformed into columnar crystals due to temperature gradient in the local area.

Molecular modelling of active oil droplet propulsion: Insights from dissipative particle dynamics simulation

This study employed dissipative particle dynamics (DPD) simulations to investigate the self-propelled motion of oil droplets in water–oil–surfactant systems. It is the first attempt to replicate self-propulsion models of oil droplets at the molecular level, contrasting previous simulations focused on Brownian motion and hydrodynamic behaviour of colloidal particles. The DPD model reproduced droplet propulsion and visualised internal Marangoni flow, showing that larger droplet radii and greater interfacial tension differences increase propulsion speeds. Additionally, surfactants with stronger oil–oil repulsion enhanced propulsion speed, suggesting that surfactant-induced local structures are crucial for the self-propulsion mechanism.

Human Mastication Analysis-A DEM Based Numerical Approach.

Mastication is an essential and preliminary step of the digestion process involving fragmentation and mixing of food. Controlled muscle movement of jaws with teeth executes crushing, leading towards fragmentation of food particles. Understanding various parameters involved with the process is essential to solve any biomedical complication in the area of interest. However, exploring and analyzing such process flow through an experimental route is challenging and inefficient. Computational techniques such as discrete element numerical modeling can effectively address such problems. The current work employs the Discrete Element Method (DEM) as a numerical modeling technique to simulate the human mastication process. Tavares and Ab-T10 breakage models coupled with Gaudin Schumann and Incomplete Beta fragment distribution models have been implemented to analyze the fragmental distribution of food particles. The effect of particle shape (spherical, polyhedron, and faceted cylinder), size (aspect ratio), and orientation (vertical and horizontal) on breakage and fragment distribution is analyzed. To account for the elastic-plastic behavior and moisture content in food particles, modifications has been made in breakage models by incorporating numerical softening factor and adhesion force. The study demonstrates how numerical modeling techniques can be utilized to analyze the mastication process involving multiple process parameters.

Effect of Process Parameters on Yttria‐Stabilized Zirconia Particles In‐Flight Behavior and Melting State in Atmospheric Plasma Spraying

The preparation of coatings by atmospheric plasma spraying gives rise to complex physical processes, which present challenges to the study of plasma jet characteristics and particle in‐flight behavior. Herein, a 3D numerical model that integrates multiple physical phenomena, including electromagnetism and thermal and gas dynamics, to simulate the heating, acceleration, and melting of particles under the thermal–mechanical effect, is developed. Meanwhile, yttria‐stabilized zirconia (YSZ) coatings are prepared under varying process parameters. The DPV‐2000 system is employed for the diagnosis of particle velocity, surface temperature, and diameter. Following comparison, the simulation exhibits errors of 4.5% and 14.8% for the maximum temperature and velocity, respectively. An increase in current intensity from 500 to 600 A results in a rise in the proportion of particles exhibiting temperatures above the melting point (2963 K), from 75.1 to 93.4%, accompanied by an increase in average velocity of ≈16.6%. As the spraying distance increases from 60 to 100 mm, the proportion of particles melting decreases from 93.5 to 66.3%, and the average velocity decreases by ≈9.2%. This work will provide a theoretical foundation for the optimization of process parameters to adjust particle behavior and melting state, thus achieving an optimal spraying effect.

Capture behavior of self-propelled particles into a hexatic ordering obstacle

Abstract Computer simulations are utilized to investigate the dynamic behavior of self-propelled particles (SPPs) within a complex obstacle environment. The findings reveal that SPPs exhibit three distinct aggregation states within the obstacle, each contingent on specific conditions. A phase diagram outlining the aggregation states concerning self-propulsion conditions is presented. The results illustrate a transition of SPPs from a dispersion state to a transition state as persistence time increases within the obstacle. Conversely, as the driving strength increases, self-propelled particles shift towards a cluster state. A systematic exploration of the interplay between driving strength, persistence time, and matching degree on the dynamic behavior of self-propelled particles is conducted. Furthermore, an analysis is performed on the spatial distribution of SPPs along the y-axis, capture rate, maximum capture probability, and mean-square displacement. The insights gained from this research serve as valuable contributions to understanding the capture and collection of active particles.

Characterization of AI-enhanced magnetophoretic transistors operating in a tri-axial magnetic field for on-chip bioparticle sorting.

We demonstrate two general classes of magnetophoretic transistors, called the "trap" and the "repel-and-collect" transistors, capable of switching single magnetically labeled cells and magnetic particles between different paths in a microfluidic chamber. Compared with prior work on magnetophoretic transistors operating in a two-dimensional in-plane rotating field, the use of a tri-axial magnetic field has the fundamental advantages of preventing particle cluster formation and better syncing of single particles with the general operating clock. We use finite element methods to investigate the energy distribution on the chip surface and to predict the particle behavior at various device geometries. We then fabricate the proposed transistors and compare the experimental results with the simulation predictions. We found that with gate electrical currents of ~ 40mA for a transistor with proper geometry, complete switching of magnetic particles with diameters in the range of 8-15μm is achieved. We show that the device is reliable and works well at different magnetic field strengths (50-100 Oe) and frequencies (0.05-0.5Hz). We also employed an image processing code with a trained convolutional neural network to automate the proposed transistors for identifying and sorting particles with various sizes and magnetic susceptibilities with accuracies higher than 98%. The proposed transistors can be used in designing novel magnetophoretic circuits for important applications in biomedical microdevices and single-cell biology.

Characteristics and fouling behaviors of soluble microbial products and sub-visible particles in an anaerobic membrane bioreactor treating sewage at room temperature

A lab-scale anaerobic membrane bioreactor (AnMBR) was employed to investigate the characteristics and fouling behaviors of soluble microbial products (SMP) and sub-visible particles (SVP) in sewage treatment. The study revealed a noteworthy trend, where SMP and SVP concentrations initially surged, subsequently declined, and ultimately stabilized at comparable levels. Compositions and fluorescent property analyses indicated that protein-like substances with tryptophan are the primary fluorescent composition in both SMP and SVP. Notably, SVP exhibited a superior protein concentration and a higher protein-to-polysaccharide ratio, thereby resulting in a higher filtration resistance than SMP. Moreover, microbial species involved in biofouling (Rhodocycales and Desulfovibrionales) also have a higher abundance in SVP, meaning SVP has a higher biofouling potential than SMP. Achievements in this study expanded the knowledge of the characteristics of SMP and SVP and revealed the significant role of SVP in membrane fouling of AnMBR.

The Dissolution Behaviors of Carbides During Solution Treatment for AMSC‐DB Ni‐Based Superalloys Fabricated by Laser‐Directed Energy Deposition and Forging

To gain insights into the microstructure evolution of as‐fabricated Ni‐based superalloys during post‐heat treatments, a comparative microstructure analysis is made based on the AMSC‐DB alloy samples fabricated by laser‐directed energy deposition (L‐DED) and forging. In L‐DED samples, the (Nb,Ta)C carbides experience a continuous dissolution process during the solution treatment. In contrast, the coarsening behaviors of carbide particles in forge alloys are observed to take place simultaneously with their dissolution. Characterization results show that the carbides in L‐DED alloy present uniformly distributed particle sizes and nodular shapes with much irregular surface curvatures. Also, less‐pronounced Nb segregation behaviors in carbide vicinity are found in L‐DED alloys. Therefore, the difference in carbide dissolution kinetics in L‐DED and forge alloys can be ascribed to the combined effects of phase morphologies and local chemical driving forces. Correspondingly, the segmented changes in grain boundary misorientations and recrystallization process in forge alloys are observed to be highly coupled with the carbide dissolution behaviors, compared to the continuous microstructural evolution in L‐DED alloy. The different recrystallization behaviors can be quantitatively reflected by the Zener pinning effect. This work sheds light on the proper design of post‐heat treatments for L‐DED alloys compared to the traditionally manufactured counterparts.