Particle Motion Patterns Research Articles

Spatio-temporal patterns of sediment particle movement on 2D and 3D bedforms

An experimental study was conducted to explore sediment particle motion in an open channel and its relationship to bedform characteristics. High-definition submersed video cameras were utilized to record images of particle motion over a dune’s length scale. Image processing was conducted to account for illumination heterogeneity due to bedform geometric irregularity and light reflection at the water’s surface. Identification of moving particles using a customized algorithm was subsequently conducted and then the instantaneous velocity distribution of sediment particles was evaluated using particle image velocimetry. Obtained experimental results indicate that the motion of sediment particles atop dunes differs depending on dune geometry (i.e., two-dimensional or three-dimensional, respectively). Sediment motion and its relationship to dune shape and dynamics are also discussed.

New weight factor for Brownian force exerted on micro/nano-particles in air flow

In order to effectively describe the effect of Brownian force exerted on the micro/nano-particles in air flow, a new weight factor, which is defined as the ratio of the characteristic velocity of the Brownian motion to the macroscopic velocity, is proposed and applied to the particle settlement under gravity. Results show that the weight factor can quantitatively evaluate the effect of Brownian force on the particle motion. Moreover, the value of the weight factor can also be used to judge the particle motion pattern and determine whether the Brownian force should be taken into account.

Numerical simulation study on the influence of incident position on erosion characteristics of gas-particle two-phase flow in 90° elbow

In gas gathering pipeline system, 90° elbow suffers constant and severe collision of gas-carrying particles, which causes serious erosion on the inner wall. In this study, models of standard elbows (carbon steel with 210 GPa in elasticity modulus and 8300 kg/m3 in density) whose diameter varies from 65 to 200 mm with curvature ratio 1.5 are established to predict erosion rate causes by silica sand (100 μm in diameter, 1550 kg/m3 in bulk density) under gas gathering operating conditions (5.0 MPa, 10 m/s). Unlike most of the previous studies which only focus on erosion result on the wall, in this article, author extracts sample particles as research objects and studies the motion of every single particle. It has been found that there are three typical types of particle motion patterns in the elbow, and a part of sand particles released from lower area of incident plane will not even cause erosion.

Movement patterns of ellipsoidal particles with different axial ratios in three-body abrasion of monocrystalline copper: a large scale molecular dynamics study

In this paper, the movement patterns of monocrystalline diamond ellipsoidal particles, which are sandwiched between monocrystalline copper workpieces, were investigated by large-scale molecular dynamics (MD).

Deposition of particles in the supersonic flow past a wedge

In our previous research, we find three particle motion patterns when submicron particles enter a supersonic laminar boundary layer over a flat plate. In these three patterns the deposition pattern is the most intriguing one because it is the lateral lift force directed to the wall that results in the particle deposition, hence the lateral deposition. In this paper, we investigate the particle motion in the supersonic flow past a wedge instead of a flat plate. The inertial deposition mechanism is introduced when the wedge replaces the flat plate. The inertial deposition is essential for the whole deposition process. Therefore, we build a two dimensional Eulerian Lagrangian numerical model to investigate this process. Several factors including particle initial position, wedge angle, initial Mach number and particle size are studied. It turns out that the higher particle has a more important lateral deposition mechanism, and as the wedge angle, initial Mach number or particle size increase, the importance of inertial deposition increases. Finally, as the three particle motion still exists in the wedge cases, we also propose a non-dimensional number to describe these patterns.

Study of Interaction Between an Axial Particle-Suspended Gas Flow and Radial Gas Jets in a Variable Cross-Section Cylindrical Channel

The results of experimental investigations of hydraulic characteristics of an axial particle-suspended gas flow in a cylindrical channel enlarged suddenly upon interaction with radial gas jets are reported. The flow velocity variation along the pneumatic pipe height and the pattern of particle motion in the pneumatic pipe are studied. It is shown that hydraulic resistance to a flow containing solids depends essentially on the radial gas jet velocity and mass solid concentration.

DEM/CFD approach for modeling granular flow in the revolving static mixer

DEM/CFD (Discrete Element Method/Computational Fluid Dynamic) approach was used to develop a three dimensional model of fluid flow and mixing process of solid particles within the revolving static mixer, type Komax. Static mixers are widely used in process industry, food industry, pharmaceutical and chemical industry. Mixing process adds significant value to the final product and it can be regarded as a key process. The quality and the price of the product often depend on mixing efficiency. Both design and operation of the mixing unit itself have a strong influence on the quality produced. In this paper, DEM is used for modeling granular flow of zeolite spheres in the revolving Komax static mixer and CFD method was used for modeling fluid flow through the Eulerian multiphase model. Coupling of these two methods provides reliable analysis of particle motion and flow pattern of the working fluid. The objective of this paper is to predict the behavior of particles after several rotations of the revolving static mixer. This type of device is used for premixing action before the main mixing process, for significant reduction of mixing time and energy consumption. This type of premixing action is not investigated in detail in the open literature. The results of the numerical simulation are compared with appropriate experimental results. The special design revolving static mixer, made of transparent Plexiglas was used for this experiment. Mixing quality was examined by RSD (relative standard deviation) criterion. Application of this model provides the optimization of the number of revolutions and geometrical parameters of mixing process taking into account the quality of the mixing process.

Abrasion wear behavior of a forged and unforged Fe-B alloy

Abstract Fe-B alloys exhibit continuous networks of eutectic borides, which destroy the continuity of matrix and result in the brittleness of the material. In order to improve its toughness, Fe-B alloy was treated by hot forging process in this study. Three-body abrasion wear behaviors of forged and unforged Fe-B alloy under three different abrasive (SiC, garnet and quartz sand) and applied load conditions were studied. Wear mechanisms were investigated by using scanning electron microscope (SEM) and 3D laser scanning microscope (LSM). The result shows that under three-body abrasion condition, Fe-B alloy exhibits excellent wear resistance. The wear resistance of forged samples is higher than that of unforged samples on the three different kinds of abrasive. A correlation between the hardness of the abrasive, movement patterns of abrasive particles and applied load was found. The movement patterns of quartz sand are sliding between the contacting surfaces under the load of 3 kg. In the wear process of Fe-B alloy, sliding/cutting is the dominant removal mechanism in the case of quartz sand abrasive and rolling is the dominant removal mechanism in the case of garnet abrasive during three-body abrasion under the load of 3 kg. When Fe-B alloys are tested under the load of 1, 3 and 5 kg, it is found that load can change the movement patterns of abrasive particles. With increasing load, the movement patterns of abrasive particles are changed from rolling to sliding mechanism. Our investigations reveal that the three-body abrasive wear mechanism of forged and unforged Fe-B alloy depends on material/abrasive hardness ratio and applied load.

Coupled CFD–DEM of particle-laden flows in a turning flow with a moving wall

The nature of the particle–solid interactions and particle–fluid interactions in rectangular duct bend geometry with/without a moving wall is studied, taking into account particle collision, colloidal, and hydrodynamic forces, and four way coupling between the fluid flow and particles. The focus is on systems where particles and fluid phase have similar length scales, fluid Reynolds number (Ref)∼1, and particle's Stokes number (St)∼1. Particles move toward the walls of the channel near the bend, and have long residence times in these regions. Buoyancy force has negligible effect on particle motion, where adhesion and drag forces lead to particle motion and agglomeration patterns. The effect of a free surface on agglomeration sites in the turning flow is elucidated.

Thermophoretic motion behavior of submicron particles in boundary-layer-separation flow around a droplet

As a key mechanism of submicron particle capture in wet deposition and wet scrubbing processes, thermophoresis is influenced by the flow and temperature fields. Three-dimensional direct numerical simulations were conducted to quantify the characteristics of the flow and temperature fields around a droplet at three droplet Reynolds numbers (Re) that correspond to three typical boundary-layer-separation flows (steady axisymmetric, steady plane-symmetric, and unsteady plane-symmetric flows). The thermophoretic motion of submicron particles was simulated in these cases. Numerical results show that the motion of submicron particles around the droplet and the deposition distribution exhibit different characteristics under three typical flow forms. The motion patterns of particles are dependent on their initial positions in the upstream and flow forms. The patterns of particle motion and deposition are diversified as Re increases. The particle motion pattern, initial position of captured particles, and capture efficiency change periodically, especially during periodic vortex shedding. The key effects of flow forms on particle motion are the shape and stability of the wake behind the droplet. The drag force of fluid and the thermophoretic force in the wake contribute jointly to the deposition of submicron particles after the boundary-layer separation around a droplet.

DEM analyses of the whole failure process of shallow foundation in plate load test on dense sand

Shallow foundations are widely used in civil engineering practice, but the instability mechanism is still unclear yet. Previously, the Finite Element Method (FEM) was commonly used to analyze the failure process of shallow foundations, but it meets difficulty in properly simulating the whole failure process of shallow foundation on the strain-softening material. Hence, the Discrete Element Method (DEM) is employed in this paper to study the instability mechanism of the shallow foundation via numerical plate load test with focus on the microscopic features evolution during vertical loading. In the simulation, an amplified gravity was applied to a dense granular ground to reproduce a gravity stress state at a large scale. Then, a plate was put on the granular ground to simulate the plate load test. Deformation pattern, particle velocity and distribution of void ratio in the ground were examined to illustrate the microscopic features in the whole failure process of the granular ground. The results show that: 1) There are a marked peak value and a settlement softening branch in the stress-settlement relationship. 2) The grids close to the edge of the plate are peculiarly extended and twisted. 3) Four particle motion patterns were observed in the velocity fields and the percentage of each motion pattern changes during loading. 4) The void ratio field varies during loading, and the distinguishing interface tends to be similar to Terzaghi's shear failure surface.

Underground pneumatic separation of coal and gangue with large size (≥ 50 mm) in green mining based on the machine vision system

Coal gangue separation is of key important for green mining. Underground pneumatic separation of coal and gangue based on the machine vision system is proposed in this study. This method has the potential to be used in coal mining due to the real time control and simple work principle. Here, the theoretical pneumatic separation distance formula of coal and gangue is derived based on energy conservation principle. Then hard-sphere model is applied to simulate the particle motion pattern in a three-dimensional model with a pressure–velocity boundary, and key factors affecting coal gangue pneumatic separation for large diameter (≥50mm) are analyzed. An air–solid multiphase flow simulation was conducted to clarify all the three factors (airflow velocity u, the conveyor velocity v0 height difference hp between conveyor belt and air nozzle) have great influence on separation distance. Especially, the optimal parameters for best separation distance are presented at u=320m/s,v0=0.5m/s,hp=0.4m. Besides, the theoretical pneumatic separation distance formula is corrected based on experiment data, the error between experiment value and calculate value of the separation distance is less than 15%. The corrected formula has important guiding significance and practical value for coal gangue pneumatic separation.

Motion of Submicron Particles in a Supersonic Laminar Boundary Layer under Hypergravity

The process of submicron particle movement in laminar boundary layers has many applicable backgrounds including high-speed centrifugal devices. Although a big progress has been made on this problem during the last decades, many mechanisms in this process still remain unclear. Here, we developed a theoretical model to understand how submicron particles will behave when they are in a supersonic laminar boundary layer above an adiabatic plate along with the main stream under both zero gravity and hypergravity. In this model, we applied the Lagrangian method to track the particles and calculate their trajectories, and the Eulerian method was used to calculate the flow field. Because of the large velocity and temperature gradient near the wall and the small size of the particle in this question, and the high gravity field, five forces (e.g., drag force, Saffman lift force, thermophoretic force, Brownian force and gravitational force) acting on the particle are considered, and the role of each force is studied. The effects of entering position, intensity of gravity field, the size and density of particles are investigated. As a result, we discovered that there are three particle movement patterns when they enter the supersonic boundary layer under regular gravity and other patterns under high gravity. This research gives a better understanding of the particle movement process in the supersonic laminar boundary layer, which can be a useful instruction for the industrial processes relating to this phenomenon.

Motion of Submicron Particles in Supersonic Laminar Boundary Layers

Submicron-particle motion in laminar boundary layers is present in many practical applications. Some important findings on this issue have been achieved during the last decades, but many mechanisms in this process still remain unclear. In the present work, a model has been developed to describe the motion of the submicron particles in supersonic laminar boundary layers above an adiabatic plate along with the mainstream. In this model, the Lagrangian method is used to track the particles and calculate their trajectories, and the Eulerian method to calculate the flowfield. The effects of the entering position, Mach number, and the size and density of the particles were investigated. It is concluded that there are three particle-motion patterns when they enter the supersonic boundary layer, which are departure pattern, equilibrium pattern, and deposition pattern. The drag force and Saffman lift force were discovered to play dominating roles in deciding the patterns, and thermophoretic force and Brownian force are of less importance. A dimensionless number to describe these three patterns is suggested. This work was intended to provide an insight into the submicron-particle motion in the supersonic laminar boundary layer, which can be guidance for industrial applications involving this phenomenon.

Tracing dust sources in different atmosphere levels of Tehran using hybrid single-particle lagrangian integrated trajectory (HYSPLIT) model

Thepresent study aims to tracing dust sources of Tehran (capital city of Iran)using HYSPLIT model and atmospheric circulationsystems atdifferent levels. The statistical analyses within the period 1981-2005 indicatethat one of the most significant dust events in Tehran province occurred in May2000 and continued for more than 4 days in Abali, Chitgar, Firuzkuh, Karaj andNorth Tehran stations. For this purpose, in order to identify the sources of dustparticles and their directions, firstly, high-level atmospheric data includingzonal and meridional wind, geopotential height at pressure levelof 700 and 850 hPa and atmospheric circulation patterns werestudied from two days before the storm, the first of May until the end of thesecond, fourth and fifth day. By using atmospheric circulation maps, the synoptic systems effective in causing dust events, flowsdirections and their speeds were determined. In this modeling approach, a backwardparticle tracking method was applied to determine the direction of dustparticles, 48 hours before dust storm in Tehran, at three elevations of 100,500 and 1000 meter. With regard to the fact that the pressure systems ofnorthern latitudes are active over Iran in transition period of spring, itshould be noted that the results of the present study were affected by thesesystems. Results indicate that the high-pressure system hovering above theSaudi Arabia and the low-pressure tongue at higher latitudes play an importantrole in forming particle motion patterns and flow speeds of mentioned levels.Using HYSPLIT Lagrangian model shows the effects of arid regions of SaudiArabia, Iraq and some parts of Syria on producing greatest amount of dustparticles transferred to Tehran.

Quantifying the Dynamic Evolution of Graded Gravel Beds Using Particle Tracking Velocimetry

AbstractThe motion of graded gravels under steady and spatially uniform turbulent flow is investigated in laboratory conditions using particle tracking velocimetry (PTV). The gravel bed is subjected to flows approaching critical armor velocity, and water worked until static armor is reached. A digital particle tracking (DPT) algorithm, based on image subtraction between subsequent frames, is developed and applied on the particle scale as the graded gravel bed is water-worked. The dynamic evolution of graded gravels is quantified continuously for up to 8 h. Characteristics of particle motion are identified, and movement patterns under complex flow conditions are analyzed. Particle tracking is applied to low-frequency (0.67-fps) and high-frequency (30-fps) data. This study provides a new perspective on gravel particle transport distances, trajectory sinuosity, sediment transport rate, fractional sediment transport rates, particle movement patterns, and instantaneous particle velocities.

Movement Patterns of Metallic Particles in a Single Phase Compressed Gas Insulated Busduct with Electromagnetic Field Effect

Movement Patterns of Metallic Particles in a Single Phase Compressed Gas Insulated Busduct with Electromagnetic Field Effect

Three-dimensional modeling of system of vibrating spherical balls using discrete element method

The modeling of particulate systems has been an important focus of research worldwide, as these are fairly common in nature, such as rain drops in air, snowfall, and several industrial processes such as chemistry, agriculture, pharmaceutical, powder metallurgy, soil mechanics, casting, cement manufacturing, civil, and etc. In recent years, one of important aspects of the granular material physics in industries is controlling way of the granular flow. One of the best ways of controlling the flow is the use of mechanical vibrations to guide the particles in desirable way. In this paper the effect of horizontal harmonic vibration on the particles flow is theoretically and experimentally investigated. During the base vibration, the spherical particles collide with each other and with the walls as well, causing a global pattern of particle motion which is interpreted as flow. The motion of spherical particles and the interaction forces due to the vibration is obtained numerically via discrete element method (DEM). Finally, the presented numerical model is compared with the experimental one and a good agreement between them is noticed.

CFD–DEM modeling of gas–solid flow and catalytic MTO reaction in a fluidized bed reactor

The methanol-to-olefins (MTO) process is currently being implemented successfully in fluidized bed reactors (FBRs) in China. Characterizing the gas–solid flow is crucial in operating MTO FBRs effectively. In this work, a combined discrete element method (DEM) and computational fluid dynamics (CFD) model is developed to describe the gas–solid flow behavior in an MTO FBR. In this model, the particles are modeled using DEM, and the gas is modeled using Navier–Stokes equations. The combined model incorporates the lumped kinetics in the gas phase to achieve the MTO process. Moreover, the combined model can characterize the heat transfer between particles as well as that between the gas and the particles. The distinct advantage of the combined model is that real-time particle activity can be calculated by tracking the motion history of the catalyst particle with respect to heat transfer. The simulation results effectively capture the major features of the MTO process in FBR. Moreover, the simulation results are in good agreement with the classical calculation and experimental data. The particle motion pattern and distributions of a number of key flow-field parameters in the reactor are analyzed based on the validated model. The effects of operating conditions on FBR performance are also investigated. The simulation results show that the particle motion exhibits a typical annulus–core structure, which promotes excellent transfer efficiency. The results also demonstrated that the feed temperature, inlet gas velocity, and feed ratio of water to methanol significantly affect reaction efficiency.

Abrasive wear of nanoscale single crystal silicon

Nanoscale three-body and two-body abrasive wear on the monocrystalline silicon are investigated using a large-scale molecular dynamics approach. A nanoscale model of three-body abrasion is proposed to evaluate the movement pattern of a sphere particle. It is concluded that the rolling movement of a particle is observed without sliding in the present nanoscale computation process. It is found that there exists a large elastic recovery which prevents the sphere particle from sliding. A modified e/h criterion is proposed to predict the movement pattern of a particle. The result confirms the crucial effect of the elastic recovery on movement pattern. The plowing is also observed as a main wear pattern in three-body abrasion at the nanoscale, whereas the wear mechanism will transform from plowing into cutting at a large indentation depth for two-body abrasion. The cutting tendency is increased with increasing indentation depth. In both the three-body and two-body abrasion, friction force is directly proportional to normal force which governs the friction rule. A turning point is found lied on frictional line related to normal force, which indicates a transition of wear mechanism in two-body abrasion. It is also examined that three-body abrasion is able to cause more massive phase transformation than two-body abrasion although it is with shallower groove in three-body abrasion than in two-body abrasion.