Average Particle Velocity Research Articles

Particle velocity profile in an inclined rotating drum

Various experimental and numerical studies have been carried out to study the velocity profiles of the particles inside horizontal rotating drums, but little emphasis has been laid on inclined rotating drums, though these drums are extensively used in granular process industries. In this study, velocity profiles of the particles in a rotating drum with 0o, 5o, 10o, and 15o inclinations have been studied by using the discrete element method. It was found that at the locations of the drum with the volumetric fill in the range of 0.2 0.8, the inclined rotating drum has a similar variation of velocity with the radial height to the horizontal rotating drum. However, the variation of the average particle velocity along the length of the drum differs for horizontal and inclined drums. Furthermore, for the inclined rotating drum, the average velocity increases with the increase in the volumetric fill.

Electrostatic Charge Distribution-Based Direct Velocity Tomography Method for Gas–Solid Two-Phase Flow

Electrostatic direct velocity tomography method (EDVT) based on electrostatic tomography (EST) is a technology that uses the induced charge signal on the electrode surface through an image reconstruction algorithm to obtain the particle velocity distribution of gas-solid two-phase flow. To simplify the calculation, EDVT assumes that the charge in the imaging region is uniformly distributed. However, due to the complexity of gas–solid flow, this assumption cannot be satisfied, which often brings great measurement errors. To solve the problem, this article proposes an electrostatic charge distribution-based direct velocity tomography (ECDDVT) method by introducing charge distribution information to improve the cross-correlation sensitivity matrix. To evaluate the effect of the particle velocity distribution reconstruction method, this article established an evaluation platform based on a three-dimensional (3-D) simulation of gas–solid flow field and electrostatic field. By assigning the weight value of the number of particles in different pixel units, a more accurate method for measuring the average particle velocity can be obtained. The simulation results and the experiment results of the belt type electrostatic velocity measurement facility show that the performance of the proposed ECDDVT in terms of image correlation coefficient and absolute percentage error (APE) is better than EDVT. The experimental results of the gas–solid two-phase flow rig show that the ECDDVT method can better reflect the particle velocity in the center of the pipe.

Towards an evaluation of bedload transport characteristics by using Doppler and backscatter outputs from ADCPs

Both the apparent bedload velocity and the backscattering strength measured by acoustic Doppler current profilers could assist bedload assessment in the field. To test this hypothesis, two ADCPs working at three frequencies (3 MHz and 1 MHz, M9; 2 MHz, StreamPro) were deployed simultaneously to measure seven different bedload transport conditions in a laboratory flume. The bedload transport was monitored by two high-speed cameras and a bedload trap. For some experiments 3 MHz and 1 MHz delivered spatially averaged apparent velocity, for others the velocity corresponded to the average velocity of particles. The 2 MHz severely underestimated the average particle velocity. The M9 backscattering strength decreased as the bedload concentration increased, independently of the size and velocity of transported particles. The 2 MHz resulted in almost constant backscattering strength. These findings demonstrate that further examination of the acoustic configurations and parameters could lead to a methodology for bedload quantification based solely on the acoustic outputs.

GPU-based DEM simulation for scale-up of bladed mixers

GPU-based DEM is used to study large-scale particle mixing in bladed mixers. A bladed mixer is scaled-up to three different sizes by maintaining the geometric similarity. Four Froude numbers are selected as the main operating conditions of bladed mixers with different sizes. The results demonstrated that the mixing quality across different mixer sizes is similar at the same Froude number, but it requires a longer mixing time to achieve similar mixing performances as the mixer becomes larger. Correlations to predict the mixing rate, average particle velocity, average total forces, average contact forces and average blade torque as functions of the scale-up ratio and Froude number (or rotation speed) are proposed. A similarity study shows that maintaining the dynamic or kinematic similarity does not produce a similar mixing performance, while maintaining the mixing rate produces a similar mixing performance across all mixers.

Changes in the Coating Composition Due to APS Process Conditions for Al2O3-Cr2O3-TiO2 Ternary Powder Blends

Thermally sprayed coatings from the single oxides and binary compositions of the Al2O3-Cr2O3-TiO2 system show multifunctional properties. Ternary compositions are promising for further improvement in their performance. The stability of the composition during coating formation is an important issue for blended feedstock powders in order to obtain the desired properties. This work focuses on the compositional changes of a ternary blend of Al2O3, Cr2O3 and TiOx powders of equal content by mass in a conventional atmospheric plasma spraying (APS) process using an Ar/H2 plasma gas mixture. By increasing the argon flow rate at constant hydrogen flow rate, the total plasma gas flow rate and the Ar/H2 ratio were varied. For the highest argon flow rate, this resulted in an average particle velocity of 140% and an average particle temperature of 90% of the initial values, respectively. Coating composition and microstructure were studied by optical microscopy, SEM, including EDS analyses, and XRD. In addition, the coating hardness and electrical impedance were also measured. Differences in the “difficulty of melting factor” (DMF) and the thermal diffusivity of the three oxides appear to be responsible for the dramatic change of the coating composition with an increasing argon flow rate. For the highest argon flow rate applied, besides TiO2, the coating contains only 8 wt.% Al2O3, while the Cr2O3 content remained almost constant. At the same time, the change of the Ar/H2 ratio resulted in the formation of stoichiometric TiO2 in the coating by oxidation of TiOx in the feedstock powder. Moreover, a small content of titanium was found in the Cr2O3 splats, showing that there are only limited interactions between the large oxide powder particles. Thus, the study has shown that stability of the chemical composition during spraying of ternary powder blends is strongly influenced by the process conditions.

Dynamical model for primordial black holes

Primordial black holes are analytically and numerically discussed based on the extended McVittie spacetime solution. By assuming that dark matter and radiation are the only sources of energy accreted by the forming central object, it is found that the black-hole mass evolution depends on the initial mass of the seed, the time in which the black hole emerges, and also on the average peculiar velocity of dark matter particles. Constraints on the initial conditions of the primordial black holes are derived from profiles of the black-hole accretion mechanism and cosmological environment. A large range of masses is compatible with our approach. In particular, masses of the order of $10^{10}M_{\odot}$ today may also be generated from small seeds. An incubation time for the emerging horizons is observed when the initial masses of the seeds are close to the particle-horizon mass. It is also argued that the McVittie-type description is consistent with the Schwarzschild solution as long as other astrophysical processes near the central object are neglected.

Settling of inertial nonspherical particles in wavy flow

Motivated by the problem of microplastics in the ocean, we experimentally investigate settling of plastic rods, disks, and spheres in wavy flows. We find that particle average vertical velocity can both increase and decrease in waves, relative to particle settling velocity in quiescent flow. This variation is a function of flow inertia at the particle length scale, characterized by particle Reynolds number Re${}_{p}$, and also of particle shape. We find that even though the relative vertical velocities between particles and flow remain constant with Re${}_{p}$, the particles nonuniformly sample the flow as a function of particle shape and Re${}_{p}$.

A chimera approach for MP-PIC simulations of dense particulate flows using large parcel size relative to the computational cell size

The Multiphase Particle in Cell (MP-PIC) is an Eulerian-Lagrangian numerical method that resolves the particle-particle interactions using the averages mapped from the Lagrangian parcels onto the Eulerian mesh. The MPPIC's accuracy depends on mesh quality and resolution, but the mesh resolution requirements for the Computational Fluid Dynamics (CFD) fields and MP-PIC models are not in accordance. This paper proposes a chimera approach, which implements two overlapping meshes in the Lagrangian-Eulerian framework with disparate length scales - a fine mesh for the CFD fields and a coarser mesh for the MP-PIC fields. The CFD fields are mapped to the MP-PIC mesh, while the coarse mesh fields, such as solids volume fraction and momentum source of parcels, are mapped to the finer CFD mesh. The National Energy Technology Laboratory's (NETL) Small-Scale Challenge Problems-I (SSCP-I) fluidized bed case is selected for simulations and model validation. A parametric study is conducted, which considers different drag and inter-particle stress models and different solids volume fraction limits. We show that the chimera approach results in a realistic turbulent flow field for accurate drag force calculations on parcels while preserving adequate conditions for the submodels’ validity under MP-PIC. The results are in good agreement with the experimental findings, specifically the pressure drop, Eulerian average particle velocity, and granular temperature. The chimera method is developed to overcome the averaging limitations when the particle size is comparable to the cell size or when particle collisions may not be captured accurately, and a finer mesh is required for the fluid flow.

Ultrasound-enhanced diffusion and streaming of colloids in porous media

Diffusion of colloidal particles in porous media is critical for the development of specially engineered colloids used to aid the recovery of oil from a petroleum reservoir. However, shielded structures, such as dead-end pores, prevent these colloids from reaching the available oil. This article examines the use of ultrasound fields as a mechanism for increasing the mobility of colloidal particles in porous media. Particle tracking of optical video microscopy experiments performed in micromodels of varying porosity are used to construct mean square displacement, from which effective diffusion coefficients and average particle velocities can be measured. We introduce an acoustic field by sweeping a phase space that consists of multiple voltages, frequencies and porosities. Our experiments show that diffusion scales linearly with voltage, while average particle velocity scales quadratically. We found that the diffusion and average velocity peaked near a frequency of ~40 kHz for porosities of 0.62, 0.76 and 0.9, suggesting the presence of a natural frequency. A second natural frequency with a value close to ~90 kHz was also observed in experiments conducted at 0.62 and 0.76. The effective diffusion at 40 kHz has a maximum value ~0.4 μm2/s, which is a factor of 5.5 times greater than in the absence of an acoustic field. Outside of the 40 kHz resonance peak, diffusion remains enhanced, with a measured coefficient of ~0.15 μm2/s. This is still a factor of 2 greater than when no acoustic field is present. Overall, our results demonstrate that ultrasound enhances the transport of colloidal particles through porous media. Future work aims to use these results as the foundation for improved modelling of acoustically stimulated transport through porous media as well as applying these results to problems related to particulate separation.

Investigating slurry erosion behavior of a hydro-machinery steel under various impingement variables

SS410 is widely used as a hydro-machinery steel and is generally exposed to the slurry erosion conditions, which decrease its useable-life. In the current investigation, an attempt was made to analyse the effect of slurry erosion on this steel. The slurry erosion testing was done in a slurry erosion test rig, which provides possibility to vary impingement conditions like average particle size, slurry concentration, impingement angle, and velocity of jet. Moreover, some mechanical and metallurgical properties of the steel were also investigated. It was concluded that the slurry erosion rate of the steel increases with increase in the concentration and jet velocity. However, with the increase in average particle size, slurry erosion was found to decrease, which may be due to the lower penetration capacity of higher sand particles. Moreover, slurry erosion, in general, was found to be maximum at a parametric combination of lowest average particle size (150 µm), 60° impingement angle, maximum concentration (45000 ppm), and maximum jet velocity (35 m/sec). Slurry erosion was found to be maximum at an impingement angle of 60°, indicating a mixed mode of erosion (ductile as well as brittle) for the given steel. The mechanisms involved in slurry erosion were found to be crater formation, ploughing, and lip formation followed by its fracture.

Dissipative particle dynamics model of homogalacturonan based on molecular dynamics simulations

In this study we present an alternative dissipative particle dynamics (DPD) parametrization strategy based on data extracted from the united-atom molecular simulations. The model of the homogalacturonan was designed to test the ability of the formation of large-scale structures via hydrogen bonding in water. The extraction of coarse-grained parameters from atomistic molecular dynamics was achieved by means of the proposed molecule aggregation algorithm based on an iterative nearest neighbour search. A novel approach to a time-scale calibration scheme based on matching the average velocities of coarse-grained particles enabled the DPD forcefield to reproduce essential structural features of homogalacturonan molecular chains. The successful application of the proposed parametrization method allowed for the reproduction of the shapes of radial distribution functions, particle velocities and diffusivity of the atomistic molecular dynamics model using DPD force field. The structure of polygalacturonic acid molecules was mapped into the DPD force field by means of the distance and angular bond characteristics, which closely matched the MD results. The resulting DPD trajectories showed that randomly dispersed homogalacturonan chains had a tendency to aggregate into highly organized 3D structures. The final structure resembled a three-dimensional network created by tightly associated homogalacturonan chains organized into thick fibres.

CFD-DEM Simulation of a Coating Process in a Fluidized Bed Rotor Granulator

Coating of particles is a widely used technique in order to obtain the desired surface modification of the final product, e.g., specific color or taste. Especially in the pharmaceutical industry, rotor granulators are used to produce round, coated pellets. In this work, the coating process in a rotor granulator is investigated numerically using computational fluid dynamics (CFD) coupled with the discrete element method (DEM). The droplets are generated as a second particulate phase in DEM. A liquid bridge model is implemented in the DEM model to take the capillary and viscous forces during the wet contact of the particles into account. A coating model is developed, where the drying of the liquid layer on the particles, as well as the particle growth, is considered. The simulation results of the dry process compared to the simulations with liquid injection show an important influence of the liquid on the particle dynamics. The formation of liquid bridges and the viscous forces in the liquid layer lead to an increase of the average particle velocity and contact time. Changing the injection rate of water has an influence on the contact duration but no significant effect on the particle dynamics. In contrast, the aqueous binder solution has an important influence on the particle movement.

Non-negative intensity for planar structures under stochastic excitation

Identification of regions on a vibrating structure which radiate energy to the far field is critical in many areas of engineering. Non-negative intensity is a means to visualize contributions of local surface regions to sound power from vibrating structures. Whilst the non-negative intensity has been used for structures under deterministic excitation due to structural forces or harmonic incident acoustic pressure excitation, it has not been considered for analyzing a structure under stochastic excitation. This work analytically formulates non-negative intensity in the wavenumber domain to investigate the surface areas on a vibrating planar structure that are contributing to the radiated sound power in the far field. The non-negative intensity is derived in terms of the cross spectrum density function of the stochastic field and the sensitivity functions of either the acoustic pressure or normal fluid particle velocity. The proposed formulation can be used for both infinite planar structure and finite plate in an infinite baffle. To demonstrate the technique, a simply supported baffled panel excited by a turbulent boundary layer as well as an acoustic diffuse field is considered and those regions contributing to the radiated sound power are identified. It is demonstrated that the non-negative intensity distribution is dependent on the stochastic excitation. It is also found that for a panel under stochastic excitation the more the non-negative intensity distribution is concentrated within the panel surface, the more efficient the panel radiates sound to the far field.

The simulation of particle movement and heat transfer in rotary kiln for plastic waste pyrolysis

The wide application of massive plastic products in our daily life leads to the rapid generation of plastic wastes. The end-of-life management of plastic wastes has become a serious public concern. Converting plastic waste to energy products is a promising solution to both energy shortage and environment pollution. Plastic waste could be converted to pyrolysis gas, pyrolytic oil and pyrolytic char after pyrolysis in rotary kiln. The loading of heat carrier in the rotary kiln has an important impact on the particle movement and heat transfer, hence affecting the distribution of gas, oil and char in the pyrolysis products. This article used quartz sand as the heat carrier to pyrolyze plastic waste, and the heat carrier loading increased from 5% to 15%. With the increase of heat carrier loading, the yield of oil and char increased, but the gas yield decreased. By the analysis of particle movement and heat transfer in EDEM, it was found that loading more heat carrier could increase both the translational velocity and angular velocity of particles. The translational velocity showed an almost linear correlation to the loading of heat carriers. A noticeable phenomenon is that the velocity profile of 5% heat carrier loading was instable with time. This is because low heat carrier loading such as 5% could not impose sufficient friction on the kiln wall, and the heat carrier bed slipped on the kiln wall from time to time. On the contrary, the slipping move did not occur in cases with heat carrier loading more than 10% because of sufficient friction on the kiln wall. At these higher heat carrier loadings, the only way to release of gravitational potential is the rolling of particles from the top position along the bed surface. This rolling mode of particle movement certainly caused high angular velocity of particles, and increased the frequency of particle contacts. With 5% heat carrier loading, the average angular velocity of particles was one magnitude lower due to the fact that particles were slipping as a whole rather than each particle rolling from the top to the bottom. Owing to the difference of particle movement at different heat carrier loadings, the heat transfer was also affected by the heat carrier loadings. The cases with more heat carrier could definitely enhance the physical contact between particles, which facilitated the heat transfer from heat carrier to plastic particles. The temperature profile from EDEM showed that the plastic waste particles were heated at a higher heating rate if more heat carrier was in the rotary kiln. Therefore, loading more heat carriers accelerated volatilization process, and reduced the retention time of volatiles. This led to the increment of oil production and decrement of gas production. In addition, the increased loading of heat carrier could maintain the temperature of particle bed at higher level to enhance the carbonation reaction of volatiles, which increased the yield of pyrolytic char. The DEM simulation provided the detailed information of particle’s movement and heat transfer, which could be used as an effective tool to interpret the experimental observation and optimize the process parameters.

One-dimensional moving window atomistic framework to model long-time shock wave propagation

We develop a long-time moving window framework using Molecular Dynamics (MD) to model shock wave propagation through a one-dimensional chain of atoms. The moving window formulation “follows” a propagating shock wave allowing us to model shock wave propagation much longer than conventional non-equilibrium MD (NEMD) simulations. This formulation also significantly decreases the required domain size and thus reduces the overall computational cost. The domain is divided into a purely atomistic “window” region containing the shock wave flanked by boundary or “continuum” regions on either end which incorporate continuum shock conditions. Spurious wave reflections are removed by employing a damping band method using the Langevin thermostat applied locally to the atoms in each continuum region. The moving window effect is achieved by adding/removing atoms to/from the window and boundary regions, and thus the shock wave front is focused at the center of the window region indefinitely. We simulate the shock through a one-dimensional chain of copper atoms using either the Lennard-Jones, modified Morse, or Embedded Atom Model (EAM) interatomic potential. We first perform verification studies to ensure proper implementation of the thermostat, potential functions, and damping band method, respectively. Next, we track the propagating shock and compare the actual shock velocity and average particle velocity to their corresponding analytical input values. From these comparisons, we optimize the linear shock Hugoniot relation for the given “lattice” orientation and compare these results to those in literature. When incorporated into the linear shock equation, these new Hugoniot parameters are shown to produce a stationary shock wave front. Finally, we perform one-dimensional moving window simulations of an unsteady, structured shock up to a few nanoseconds and characterize the increase in the shock front’s width.

Study of dielectric particles motion in traveling and standing electrostatic waves using particle tracking velocimetry

The accumulation of dust and airborne particles on solar panels drastically reduces the quality of the produced energy. A promising solution consists of using traveling and standing electric waves to clean the solar panels or to avoid particle deposition on their surface. This work aims to better understand the motion mechanisms of micrometer-sized particles under the effect of electrostatic traveling and standing waves, by characterizing their displacement velocity using particle tracking velocimetry (PTV). In this experimental work, the particles motion is recorded using a high speed camera. Then, a PTV based post-processing has been carried out to get velocity vectors of individual particles based on Lagrangian approach. The velocity profiles in both and axis have been studied as a function of voltage, frequency, and particle size. The results show that the particles pass through levitation, falling, and acceleration phases during their motion. Increasing the voltage leads to a higher velocity. The small particles are more likely to be trapped in the electric potential wave because they are less affected by gravitational and drag forces. That makes their velocity higher than the bigger ones. The average velocity of particles goes through a maximum as a function of frequency in the forward direction of the traveling wave conveyor, and in both directions of the standing wave conveyor. The maximum displacement velocity in the traveling wave conveyor is higher than that obtained in standing wave one.

DEM study on the effects of pellet characteristics on particle flow in rectangular hopper

In this work, a non-cohesive and multi-element particle model of discrete element method (DEM) was constructed, which was used in combination with experiments to investigate the particle flow characteristics in retangular hopper equipped with the screw discharging machine. On this basis, different diameter pellets (dp = 20 mm, 25.02 mm) with various sphericities (φ = 0.868, 0.985, 1) and particle size distribution (a = 0:1, 0.1:0.9, 0.15:0.85, 0.2:0.8) were selected to examine the effects of sphericity and particle size distribution on the distribution of particle average velocity, motion distance and voidage. Our results showed that as the a increased, the particle average vertical velocity was first decreased and then increased. The motion distance of particles at 1/2 bed height was relatively stable. Furthermore, the average voidage of cylindrical particles was the largest and that of ellipsoidal particles was the smallest. Finally, the specific position of the lag of particle motion is revealed.

End wall effect on particle motion in a chute flow

The influence of the end wall of a chute on the rotation of internal characteristic particles is mainly on the z-axis. A measurement device based on inertial measurement technology does not require the assistance of external information; hence, it is especially suitable for measuring the angular and translational velocities of internal characteristic particles. To study the influence of the end wall of the chute on the motions of the internal characteristic particles, the z-axis rotational and translational velocities of the internal characteristic particles in the chute were measured, and it was found that the rotational velocity about the z-axis differs according to the initial position. The z-axis angular velocity of a characteristic particle at the centre fluctuates near 0, and the average value approaches 0. The z-axis angular velocity of a characteristic particle at the left end wall is typically negative. This phenomenon is due to the influence of the end wall on the rotational motions of particles with initial positions that are near the end wall. In addition, the average translational velocity of the characteristic particles is also affected by the end wall. The distributions of the average z-axis angular velocity and the average translational velocity are quantitatively analysed, and the correlation between the tilt angle of the chute and the end wall effect is studied.

Responses of macroinvertebrate functional traits to riverbed structure of typical debris flow gullies in the upper reaches of the Yangtze River, China

Debris flow is a typical natural disaster in mountainous areas. Its occurrence has serious impacts on the ecological environment and the life, property safety of local people. The structure of mountain riverbed plays an important role in maintaining the ecological stability of debris flow gullies (DFGs) and improving the ecological condition. However, the effects of hydro-geomorphological processes induced by riverbed structure on local macroinvertebrates have not been well examined. A functional approach was applied to macroinvertebrate data collected in a field survey at sites with different riverbed structure to investigate the response of macroinvertebrate functional traits and environment factors to riverbed structure-induced processes. Riverbed structure was quantitatively calculated by concavity-convexity degree. The results showed that (a) Macroinvertebrates were mainly composed of individuals with the ability of avoiding risks and recovering quickly in DFGs. (b) The environmental factors affecting macroinvertebrates (i.e., average particle size, velocity, flow rate, water depth, and gradient) had a great relationship with riverbed structure. (c) Only 3 (trophic habit, attachment and drift) of the 10 benthic functional traits in the study area had a good correlation with riverbed structure. This study thus found that riverbed structure, as a complex of various environmental factors directly or indirectly affected the community structure and functional traits of macroinvertebrates in DFGs. Besides, it was more suitable for macroinvertebrates of different species to live, and more conducive to the maintenance of ecological stability when the concavity-convexity degree value was about 0.075. Because 5 environmental factors affecting macroinvertebrates were moderate when the degree of concavity was about 0.075. These results can provide scientific basis for ecological conservation and management in DFGs where eco-environment is very fragile.

Characterization of acoustic material at oblique incidence using a spherical microphone array.

This paper proposes two distinct methods for estimating the surface impedance Zs of acoustic materials using a spherical microphone array. The first method is based on the spherical ambisonic representation of sound fields to estimate the normal particle velocity and the sound pressure at the surface of the material. The second method uses an optimization process, where the measured sound pressure field is constrained to match a theoretical model. These two methods are compared to two existing methods: the equivalent source approach and the two-microphone measurement technique. The results show a clear advantage of the microphone array methods compared to the classical two-microphone method. The measurements show an accurate reconstruction of surface impedance and absorption coefficient between 120 and 5000 Hz for various sound incidences but also show edge effect perturbations due to the limited size of the tested samples. In addition, two criteria are proposed, one estimating the noise floor level allowing the optimization of the measurement results, the other evaluating the area of accurate impedance reconstruction on the surface of the material.