Behavior Of Particles Research Articles

Shape-dependent aerosol dynamics in indoor environments: Penetration, deposition, and dispersion

Particle shape exerts a significant influence on their dynamic behavior, and it is imperative to elucidate these effects given the potential for severe environmental toxicity associated with shaped particles. Despite extensive research on the dynamical processes of spherical particles, the behaviors of non-spherical particles have been insufficiently investigated. In this study, we have developed a suite of computation-based models that account for particle shape and have reported on the typical dynamical behaviors of non-spherical particles within indoor environments. We have explored three typical scenarios, i.e., particle penetration into indoor spaces through building cracks, indoor particle deposition, and indoor particle dispersion. The shape-induced deviations are associated with dynamical processes, showing a decrease trend among penetration, deposition, and dispersion of the non-spherical particles. The maximum discrepancy due to particle shape during the penetration process exceeds 1000 %, observed with particles of approximately 0.02 μm in diameter interacting with straight cracks 4.5 cm in length and 0.25 mm in height. Moreover, there is a discrepancy of more than 70 % in the deposition of particles with a diameter of approximately 10 μm on side walls when using side air supply ventilation. Similarly, a discrepancy of nearly 11 % is noted for particles around 0.02 μm in diameter during dispersion under displacement ventilation within indoor settings. The interaction between shape-related particle dynamics, particularly their diffusion characteristics, and the properties of the flow field leads to these shape-dependent dynamical discrepancies. These findings offer a comprehensive understanding of how the shape of particles affects their indoor dynamic behavior, thereby supporting the control of hazardous particles in indoor environments.

Double Mpemba effect in the cooling of trapped colloids.

The Mpemba effect describes the phenomenon that a system at hot initial temperature cools faster than at an initial warm temperature in the same environment. Such an anomalous cooling has recently been predicted and realized for trapped colloids. Here, we investigate the freezing behavior of a passive colloidal particle by employing numerical Brownian dynamics simulations and theoretical calculations with a model that can be directly tested in experiments. During the cooling process, the colloidal particle exhibits multiple non-monotonic regimes in cooling rates, with the cooling time decreasing twice as a function of the initial temperature-an unexpected phenomenon we refer to as the Double Mpemba effect. In addition, we demonstrate that both the Mpemba and Double Mpemba effects can be predicted by various machine-learning methods, which expedite the analysis of complex, computationally intensive systems.

The Cumulation of Debris Clouds around a Fast-rotating Asteroid

Abstract The rotational mass loss has been realized to be a prevalent mechanism to produce low-speed debris near the asteroid, and the size composition of the asteroid’s surface regolith has been closely measured by in situ explorations. However, the full-scale evolution of the shedding debris has not been examined using the observed particle sizes, which may hold vital clues to the initial growth of an asteroid moonlet and help us to understand the general mechanisms that dominate the formation of asteroid systems. This paper presents our study on the cumulative evolution of the debris cloud formed by a rotationally unstable asteroid. A semianalytical model is developed to characterize the spatiotemporal evolution of the debris cloud posterior to a shedding event. Large-scale discrete element method (DEM) simulations are performed to quantify the clustering behavior of the debris particles in the mechanical environment near the asteroid. As a result, we found that the cumulation of a steady debris cloud is dominated by large pieces of debris, and the shedding particles follow a common migration trend, which fundamentally determines the mass distribution of the debris cloud. For the accretion analysis, we sketched the life cycle of a debris cluster and showed its dependency on particle size. The DEM simulations adopt physical parameters estimated from observations and asteroid missions. The results confirm that porous fluffy cluster structures can form shortly after a shedding event with magnitudes the same as the observed shedding activities. Measurements of these structures show that they themselves possess a certain strength and have the capacity to collisions to absorb dissociative particles that collide with them.

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

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.

Study on the surface texture-microparticles synergistic lubrication mechanism of artificial joint

Abstract After total joint replacement surgery, frequent injection of lubricating substances is required due to lubrication failure caused by the absorption of lubricants by the human body, which will cause serious physiological and psychological burdens on patients. In this study, with the help of surface texture aggregation of particles, gelatin microgel particles with a diameter of about 4 µm were used as lubricating substances to achieve aggregation in the texture, thus improving the friction environment under low-concentration lubricants. The study found that the rectangular cross-section texture demonstrated the most effective anti-friction properties, resulting in a 26% reduction in friction coefficient compared to non-textured surfaces. Additionally, utilizing COMSOL for particle flow simulation, researchers observed the motion behavior of particles within the texture and clarified the mechanism of particle aggregation and the improvement of lubrication on the surface. This article confirms the beneficial effects of combining surface texture and particles on lubrication, thus providing valuable insight for improving lubrication in dilute particle solutions.

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)].

Influence of Binding Energies on Required Process Conditions in Aerosol Deposition

AbstractWith the high interest in aerosol deposition in order to form high-quality coatings by solid-state impact, there is an increasing demand for developing general guidelines to estimate needed particle velocities and thus process parameter sets for successful deposition of ceramic materials. By using modeling approaches, rather different material properties in first instance can be expressed in terms of binding energies. Needed velocities for possible bonding can then derived by impact simulations and compared to experimental results from the literature. In order to study the role of binding energy on the impact behavior of ceramic particles in aerosol deposition, a molecular dynamics study is presented. Single-particle impacts are simulated for a range of binding energies, particle sizes and impact velocities. The results show that increasing the binding energy from 0.22 to 0.96 eV results in up to three times higher characteristic velocities corresponding to the threshold of bonding or grain size-dependent fragmentation of the particles. However, regardless of the binding energy, exceeding the characteristic velocities results in a similar deformation and fragmentation pattern. This allows for a general representation of the impact behavior as a function of normalized impact velocity for different ceramic materials. Apart from dealing with prerequisites for bonding of different materials by aerosol deposition, this study could also be generally relevant to the high-velocity deformation behavior of ceramics with different grain sizes.

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.

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.

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.

Particle-Scale Research on the Unsteady Gas-Solid Flow in the Launch System with a Complex Charging Structure

Abstract This work is focused on the the intricate behavior of gunpowder particles in a dynamic gas-solid flow with sudden spatial changes, crucial for the stability in a launch system (LS) with a complex charging structure. The 3D particle-scale gas-solid flow model is developed to explore particle detail characteristics in the LS with the hollow base projectile by the CFD-DEM method. The results show that the dispersion of particles characterized by slope stacking and the horizontal stacking when particles are stationary. The axial length of horizontality is 164mm, and the thickness of it is 43mm. The majority of particles are concentrated in the sloped area, and the total length of the three slope stacking is 551mm. The height of the slope shape in the chamber changes exponentially along the axial position, while that of the slope shape in the groove increases linearly along the axial position.