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Food powders often exhibit hydrophobic surface areas. To understand the effect of corresponding wettability variations on particle floating, which critically influences powder reconstitution, we studied floating of glass beads after creating surface heterogeneity by spraying cocoa butter. Force-position curves were recorded to characterise contact line pinning. Floating of particles with surface heterogeneities comprised a dynamic phase, which to our knowledge has not been reported previously. Measured forces varied due to contact line pinning/depinning. The results indicate that the dynamic floating phase is caused by gradual depinning. Steady-state floating is reached once pinning is sufficiently pronounced. We also demonstrate that surface heterogeneities complicate theoretical predictions of particle floating. The use of sessile drop contact angles for modelling was identified as an important source of error, as weak pinning points can affect contact angles but are oftentimes overcome during floating. Moreover, local pinning effects are not necessarily represented by a sessile drop. [Display omitted] • Distributed hydrophobic defects significantly affect particle floating. • Floating of particles with surface heterogeneities comprises a dynamic phase. • The height of the wettability contrast affects floating position and kinetics. • Force-position curves show contact line pinning at surface defects. [ABSTRACT FROM AUTHOR]

In order to reduce the particle addition in closed-cell aluminum foam, the effect of particles on foam drainage behavior was investigated numerically. The coupled CFD-DEM method was used to analyze the particle behavior within the node-PBs system. The predicted results agree well with experimental results. The results show that the trajectory of particles in metallic foam is consistent with literatures. Particles grow into clusters and deposit on the oxide film, leading to foam clogging and suppressing the drainage in aluminum foam. The above mechanism explains the phenomenon in literatures that the viscosity obtained from the drainage experiment is much greater than the apparent viscosity of the particle-melt mixture. The effect of particles on suppressing drainage is summarized as the blockage effect of stationary particles and the increasing apparent viscosity of moving particles. There is an optimization possibility of particle size and volume fraction, achieving better performance and lower production costs. [Display omitted] • Motion, growth, and deposition of particles in node-PBs system are investigated. • Clusters causing foam clogging is an important mechanism to suppress drainage. • Foam clogging by particles can explain high viscosity in drainage experiments. • Possible optimization approaches for particle parameters are proposed. [ABSTRACT FROM AUTHOR]

Food powder reconstitution is frequently compromised by powder floating. Although particle floating has been studied for many years, several common properties of food powders have not been considered. To elucidate the effect of dissolution and hydrophobic surface defects, floating of pure and partially coated spherical sucrose beads was analysed. It was found that floating of soluble particles is characterised by a gradual increase of immersion depth which proceeds until the particle is fully engulfed and detaches from the interface. The duration of floating depends on initial floating position, immersion and dissolution velocity. Floating of partially coated beads is additionally affected by contact line pinning at coating material. Theoretical predictions, based on force balance analysis did not reflect the observed floating behaviour indicating that dissolution requires consideration of further factors. Particularly the observed formation of a convection current, which creates an additional downwards drag, is suggested to play a decisive role. [Display omitted] • Distributed hydrophobic defects are sufficient to induce particle floating. • Floating of soluble particles is limited in time. • Initial immersion depth, immersion and dissolution velocity affect floating time. • Dissolution of a floating particle results in the formation of a convective flow. [ABSTRACT FROM AUTHOR]

Terminal Settling velocity (V ts) is a significant phenomenon for two-phase solid-liquid flows in various process units, such as slurry pipeline, annular drillpipe, fluidized bed reactor, drier, and gasifier. A two-phase system operated below V ts encounters several technical issues, such as solid accumulation, surface wear, erosion, flow irregularity, increased energy requirement, and backflow or, even, bursting. Measuring and predicting the V ts of spherical and non-spherical particles in rheologically different fluids are of interest to the concerned research community. Although many empirical models with limited boundary conditions were proposed earlier, the application of artificial intelligence (AI) for such modeling is still in infancy. In the current study, we attempt to address the shortcomings of the previous methods of predicting V ts by using a generalized machine learning (ML) approach. The training and testing of the ML models were conducted using an extensive dataset including various particle shapes and fluid rheologies. The current dataset is substantially larger compared to the similar datasets used for previous studies. We investigated several state-of-the-art ML algorithms, including ensemble learning and multi-stage regression models to find out the most optimum model for predicting V ts. The proposed model is applicable to spherical and non-spherical particles in both Newtonian and non-Newtonian fluids. This new application of AI-based modeling in the field of engineering can be used for industrial-scale design and operation with much needed reliability in a cost-effective manner. [Display omitted] • Artificial intelligence (AI) was applied to predict terminal settling velocity. • Ensemble learning and multi-stage regression models were tested. • A large dataset comprising 3328 samples was used for training and testing. • The validated model is independent of particle shape and fluid rheology. • The outcome of the current study is a generalized machine learning model. [ABSTRACT FROM AUTHOR]

Fluidization regimes for alginate aerogel particles with two different particle sizes were characterized in a laboratory scale Wurster fluidized bed both in the annular zone and the tube zone. For both particle sizes, minimum fluidization and bubbling regimes were observed in both of the zones whereas pneumatic regimes existed only in the tube zone. Moreover, a new regime which was horizontal circular motion was identified for large particles in the tube zone. There existed two other regimes in the bed which were turbulent and circulatory particle motion regimes. All fluidization regimes were mapped on Kunii and Levenspiel diagrams. Circulatory particle motion regime was given on these diagrams for the first time. Furthermore, effects of particle size, batch volume, Wurster tube size, perforated plate geometry and partition gap height on the boundaries of each fluidization regime were investigated by measuring superficial air velocities at the onset and the end of each regime. [Display omitted] • Fluidization regimes for aerogel particles were studied in a Wurster fluidized bed. • A new regime which was horizontal circular particle motion regime was observed. • Six fluidization regimes for particles were mapped on Kunii-Levenspiel diagrams. • Circulatory particle motion was mapped on these diagrams for the first time. • Effects of particle size, design and operating parameters were investigated. [ABSTRACT FROM AUTHOR]

The cooling channel can capture both the droplets and particles in the industrial waste gas. The flow field and particle motion in the corrugated cooling channel were numerically simulated and the capture mechanism was investigated. Submicron and micron particles are captured under the actions of thermophoresis and inertia, coupling with turbulence, respectively. The capture probability shows a high distribution for particles near the wall, and a low distribution for particles in the central area. The deposition probability density distribution of particles on the channel wall changes periodically along the flow direction. The overall capture efficiency decreases first and then increases with increasing particle size for submicron particles, in the range of 40% to 50%, and it keeps increasing with particle size for micron particles, reaching 77% for 10 μm particles. A corrugated cooling channel performs well in capturing particulate matter with the help of thermophoresis and inertia coupled with turbulence. Unlabelled Image • Particle capture by a corrugated cooling channel was numerically studied. • Particles are captured by thermophoresis and inertia coupled with turbulence. • Capture probability at inlet and deposition distribution on wall were revealed. • The overall capture efficiency ranges in 40%–50% for submicron particles. • Capture efficiency increases with micron particle size, reaching 77% at 10 μm. [ABSTRACT FROM AUTHOR]

Industrial bulk material transfer and handling processes often result in large dust emissions and seriously threaten workers' health. Both dust dispersion and ventilation for dust removal are related to the entrained air flow field under the particle flow fall process. The PIV test system is used to test the entrained air flow field during the particle flow free and adheres wall fall process. The particle flow free fall process: The entrained air velocity show a Gaussian distribution at the different height sections. The particle diffuses mainly along the width-side(d), and the diffusion phenomenon is not obvious in the length-side(l) direction. The particle flow adheres wall fall process: When s/d ≤ 5, the existence of the vertical wall has a significant effect on the entrained air flow field, and the entrained air can better adhere to the vertical wall. When s/d >5, the existence of the vertical wall has a little effect on the entrained air flow field, and the entrained air is basically separated from the vertical wall. This study provides a theoretical basis for the ventilation design of industrial particulate transport systems Unlabelled Image • First , The model of particle flow adheres wall fall process has presented. • Second , The PIV test system is used to test the entrained air flow field. • Third , The study provides a theoretical basis for dust control and collection system. [ABSTRACT FROM AUTHOR]

Particulate solids or fragments are found in nature and many industrial processes. They are commonly characterized by a number of morphological parameters, for which the mathematical expressions in literature usually come from comparisons to idealized shapes. Whereas these expressions must fit some requirements firstly on common geometric shapes before being used on a real solid particle. In this work, the expressions for calculating morphological parameters based on both projected area (2D) and on three-dimensional (3D) shapes of solid particles were evaluated. Hereof expressions from literature related to the same morphological parameter were identified, and others defined originally on projected area, 2D, were proposed to be used on 3D shapes. The results allowed to indicate the most suitable expression for each parameter based on pre-established criteria. In practice, distinct values obtained from different expressions applied to the same shape make a comparative analysis a complex task, which requests commitment for Standardization. Unlabelled Image • Expressions of morphological parameters were evaluated by using common geometric shapes. • From literature, expressions related to the same morphological parameter were identified. • Extension from these based on projected area (2D) were proposed to be used with 3D shapes. • Based on three pre-established criteria, the most suitable expressions were indicated. [ABSTRACT FROM AUTHOR]

In the present work, experimental studies were conducted to examine the gas-slurry interfacial shear stress and frictional pressure drop in the presence and absence of surfactant in a rectangular slurry column. A novel mechanistic model has been proposed by considering the energy dissipation rate because of bubble formation, a slip of gas-slurry interface, and the wetting of a thin liquid layer with the column wall. A comprehensive investigation was carried out to enunciate the effect of particle loading, particle size, bubble size, and surfactant on the frictional pressure drop and bubble-slurry interfacial shear stress. Generalized empirical correlations were also developed based on the dynamic variables, geometric variables, and physical properties of the system. Unlabelled Image • Phenomena of frictional pressure is analyzed in a rectangular slurry bubble column. • Bubble-slurry interfacial shear stress is interpreted by a mechanistic model. • Physiochemical effect on bubble-slurry interfacial phenomena is explained. • Rate of energy dissipation by wetting phenomena is enunciated. • Bubble formation effect on interfacial friction factor is explained. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the arching phenomenon in granular assembly. A series of two-dimensional trapdoor tests were conducted using model particles coated with a thin photoelastic sheet. Digital photo images of the model particle assembly were continuously taken during the tests, and the force of each model particle was quantitatively evaluated using a digital RGB photoelastic analysis. The test results showed that two arch structures were initially generated with trapdoor yielding, and the inner arch gradually expanded to the outer arch, while the outer arch became more solid. Given that the force per particle in the arch structure did not change significantly during the arch formation process, we concluded that the arch formation process progressed through the transmission of the force chains rather than by a change in the magnitude of the particle force. Unlabelled Image • Inner and outer arches are generated and finally outer arch only remains. • Size of arches are proportional to the trapdoor width. • Overburden pressure affects the solidity of the arch structure. • Arch formation progresses through the transmission of the force chains. • Arch formation does not change the average particle forces. [ABSTRACT FROM AUTHOR]

The collision between a single-sphere and a double-sphere is measured in this study by a high speed camera to verify the fundamental issue of tangential and normal restitution coefficients for a particular shape of double-sphere. In this experiment, a single-sphere moves and collides on a stationary double-sphere, and a high speed camera is used to capture the collision of them. Numerous tests were performed by varying the pre-collisional inclinations and pre-collisional velocities of the single-sphere. Two different definitions of the kinematic coefficient of restitutions, both normal and tangential, have been scrutinized by the experimental data to see which one is realistically true or reasonable. After comparison, the contact-point (surface) based definition is the right one which has almost case-independent value for the restitution coefficient, either in the normal or tangential direction. This verifies a key point which would be very useful for modeling the rigid body collisions, either spherical or non-spherical. Unlabelled Image • For spheres, normal & tangential coefficients of restitution (COR) are constants. • For non-spherical (NS), only COR defined by contact point's velocities is correct. • For NS, it is incorrect to define COR by post- & pre- velocities of mass centroids • Correct COR definition is independent of velocity, inclination, & particle shape. • Tangential COR also exists for NS although it has a negative constant value. [ABSTRACT FROM AUTHOR]

We propose a novel electrophoretic wet classification method using the applied electric field strength as an operation parameter. The influence of the applied electric field, electrolyte concentration, and particle size on the electrophoretic mobility was directly evaluated by microscopic electrophoresis. For high electrolyte concentrations or small particles, the electrophoretic mobilities decreased with decreasing applied electric field, unlike the basic theory of electrokinetic phenomena. We then fabricated an electrophoretic classification device and investigated the separation efficiencies for various particle sizes, electrolyte concentrations, and applied electric fields. Finally, we performed a classification experiment using the applied electric field as an operation parameter. The applied electric field that provided the highest classification performance was the same as that where the difference in the separation efficiency was the highest. These results highlight the possibility of electrophoretic wet classification using the applied electric field strength as an operation parameter. Unlabelled Image • Wet classification using the electric field as an operation parameter was proposed. • Mobilities of small particles decreased with decreasing applied electric field. • Separation efficiency varied depending on electric field and particle size. • Classification performance changed according to applied electric field. [ABSTRACT FROM AUTHOR]

Large quantities of PM (particulate matter) produced in the construction process poses hazard for both the workers ' health and the whole environment. Despite the wide application of cartridge filters to PM collection, incomplete cleaning often occurs during pulse-jet cleaning of common nozzles. In this study, a built-in rotator used in a larger-diameter pleated filter cartridge was developed to improve the effect of pulse-jet cleaning. Then, the pulse-jet cleaning performances between the built-in rotator and the common nozzle were compared. The results show that the pressure drop of the built-in rotator is similar to that of the non-built-in one under the same superficial filtration velocity. The number of rotations grows with the increase of high-pressure air, while it first increases and then remains stable with the sustained pulse time. For the common nozzle, the cleaning effect is influenced by the nozzle diameter and the jet distance. The optimum jet distance declines with the increase of nozzle diameter. Compared with the common nozzle, the pulse-jet cleaning frequency of the built-in rotator reduced from 11 to 9, the average pulse-jet cleaning interval extended from 4667 s to 5402 s, the average residual pressure drop decreased from 118.39 Pa to 86.04 Pa and the average pressure drop reduced from 243.01 Pa to 232.52 Pa. Despite the average peak dust emission concentration increased from 13.52 mg/m3 to 14.34 mg/m3, the average dust emission concentration decreased from 2.56 mg/m3 to 2.51 mg/m3. Therefore, it is proved that the built-in rotator can improve the performance of pleated cartridge filter. Unlabelled Image • A novel built-in rotator was developed to improve the performance of cleaning. • The number of rotations was selected to evaluate the effect of pulse-jet cleaning. • Optimum common nozzle was obtained by measuring residual pressure drop. • The built-in rotator reduced the average pressure drop and the total dust emission. [ABSTRACT FROM AUTHOR]

The transfer of charge between a solid sphere and a metal plate during an oblique collision has been studied, using larger, more compliant elastic spheres than in previous studies. This relatively slow collision with large maximum strain allowed the normal and tangential impact forces to be measured directly, and the cumulative rolling and sliding contact areas to be deduced using a dynamic model. A rich variety of charging behaviour was observed for different collision regimes, and suggests very different charge transfer mechanisms for sliding, non-sliding, heavy and light contact. The charge transfer to initially-negative and initially-positive spheres was also strikingly different. Although the reasons for this could not be definitively determined, several hypotheses are discussed in detail, including mechano-ion transfer, bulk material transfer, and the effect of the spatial distribution of the initial charge on the statistical distribution of charge transfer events. Unlabelled Image • Collision between elastomer spheres and metal target studied. • Charge transfer and collision forces measured. • Charging mechanism appears very different for light/heavy and normal/oblique collisions. • Transferred charge strongly dependent on polarity of initial charge. • Varying combination of electron, mechano-ion and bulk material transfer hypothesised. [ABSTRACT FROM AUTHOR]

Abstract Discrete Element simulations were carried out to model the sandpile formation with micro-sized spherical particles, with aim to gain in-depth understanding of particle spreading processes involved in additive manufacturing. Analysis of the piling process demonstrates that the friction and particle size distribution are the two key factors that control the structural properties of the sandpile. Both sliding friction and rolling friction hinder the particle flowability, leading to a higher angle of repose and a lower packing fraction of the sandpile. When the sliding friction is high, the rolling friction predominantly affects the final sandpile morphology, and vice versa. Interestingly, the effect of the rolling friction vanishes when its coefficient exceeds 0.4 due to multiple rolling restrictions. There is a competing effect for the particle size distribution: on one hand, with different sized particles, both the packing fraction and the angle of repose are reduced; on the other hand, when the size segregation is significant, the small particles sink down to fill the gaps between the big-particles, greatly enhancing the packing fraction and reverting the angle of repose to the value of single size distribution case. The present work not only provides an in-depth understanding of the particle piling mechanism under various working conditions, but also presents a practical way to extract particle properties for optimizing the additive manufacturing processes. Graphical abstract Unlabelled Image Highlights • Discrete element simulation of sandpile pouring and formation process • Dynamics analysis of particle sandpile characteristics • In-depth understanding of various factors that affect the particle packing condition. • Evaluation of particle packing mechanism • Predicting and guidance of particle deposition for additive manufacturing technology [ABSTRACT FROM AUTHOR]

Abstract Liquid-solidtwo-phase wall turbulent flow is an important flow pattern in engineering field. Studying the modulation of particles on fluid plays a significant role in revealing the mechanism of momentum, heat and mass transfer, improving production efficiency and decreasing energy consumption. The statistical characteristics and coherent structure in the flat plate turbulent boundary layer in clean water condition and near-neutrally liquid-solid two-phase flow with 200 um polystyrene particles (d p + = 2.29 , d p + = du τ v) measured by means of PIV technique were compared and analyzed. The variation rule of turbulent statistic characteristics such as mean velocity profile, turbulence intensity and Reynolds shear stress of fluid with polystyrene particles and clean water under the same free flow velocity was investigated. Based on the locally-average velocity structure function and condition sampling technique, the coherent structure was detected, and the two-dimensional spatial topologies such as the fluctuation velocity, Reynolds shear stress and spanwise vorticity in ejection and sweep events at different wall heights under two working conditions were extracted with phase-average method. It was found that in the buffer layer the flow velocity with particles was greater than that of clean water, while there was little difference between them in the logarithmic law region. Compared with the clean water, the streamwise turbulent intensity was decreased in particle-laden flow, whereas the normal turbulent intensity, the comprehensive turbulence intensity and the Reynolds shear stress were all increased, with the expense of a slightly increase of the friction drag in the fluid with particles by 3.57%. In the bursting of coherent structure, the addition of polystyrene particles suppressed the fluid streamwise fluctuation in a turbulent boundary layer, gave a rise to the normal fluctuation and Reynolds shear stress, while inhibited the streamwise development of the spanwise vortex and promoted its normal development. The addition of particles facilitated the fluctuation of the fluid microcluster, and as well as the transverse momentum transfer in the log law region of turbulent boundary layer. The particles could increase the probability of the coherent structure ejection events and had less influence on the sweep events. The number and intensity of the ejection event was the key to improve the flow normal turbulence intensity and even to improve the energy exchange near the wall. The presence of appropriate scale particles in wall turbulence could play an important role in strengthening the transfer of momentum, heat and mass, and promoting mixing and reaction in the engineering, only by slightly increasing the fraction resistance. Graphical abstract Unlabelled Image Highlights • Spatial topology of coherent structure in particle-laden flow was studied by PIV. • The wall-normal fluctuation and Reynolds shear stress were increased by particles. • The particle restrained streamwise and promoted normal spread of spanwise vortex. • Ejection frequency and intensity was the key to promote turbulence by particles. • Appropriate scale particles in wall turbulence could strengthen momentum transfer. [ABSTRACT FROM AUTHOR]

Abstract Vertical separation occurs in the binary granular system and varies with most factors of external excitation and particle properties, that is complex to explain and predict. We propose that it can be discussed from two aspects: 1) the influence of the specific external-excitation condition and 2) the separation response of the system itself. Based on the percolation and filling behaviors of particles, a vertical separation criterion is presented to discuss the above two aspects with vibration frequency f , dimensionless vibration acceleration Г , airflow velocity u , particle size ratio φ d , density ratio φ ρ and total mass ratio φ M when the container size and the granular system's packing height are fixed. In our criterion, Brazil nut separation (BN, large particles rise to the top), reverse Brazil nut separation (RBN, large particles sink to the bottom), and their crossover line (It can present as a MIX distribution where particles mix uniformly) are discussed. It's found that the system with strong separation response (a low φ M / φ d 3 φ ρ) tends to show a strong BN or RBN separation under appropriate conditions of vibration and/or airflow. Conversely, the system with weak separation response (a high φ M / φ d 3 φ ρ) inclines to separate weakly or mix uniformly. Graphical abstract Unlabelled Image Highlights • Separation criterion is derived with external excitation and particles properties. • The influence of the specific external excitation condition is discussed. • The degree of separation response of the granular system itself is discussed. [ABSTRACT FROM AUTHOR]

Caking of crystals leads to a great deal of negative impact on the quality of products leading to extra cost to restore the products to its original state before caking. It is therefore an undesired phenomenon that should be investigated and inhibited. This review considers particle issues (particle science and technology) in a crystallization view (crystallization science and engineering). 1. Characterization. Caking indices and the relevant characterization methods are classified. Their advantages and disadvantages are summarized. Particularly, potential novel characterization methods, e.g. image analysis technique and its application in analysis of caking ratio, are discussed. 2. Mechanisms. Caking process is organized into three stages: moisture sorption, then liquid bridge, and finally crystal bridge. The mechanisms are reconsidered with recent studies (e.g. mass transfer, adhesion effect of liquid bridge, kinetic of crystal caking) and crystallization science (e.g. nucleation and growth theory, polymorphism, and phase transition). 3. Prevention. Based on particle and crystal engineering, prevention of crystals caking is discussed through controlling ambient conditions (relative humidity, temperature, liquids screening, and pressure) and improving anticaking property of crystals (particles size, particles shape, impurity, and anticaking agent). A potential method of simulating crystal caking behavior based on discrete element method (DEM) and caking mechanisms is presented. With the aid of simulation, the enhanced design of particle and crystal engineering would be available, which could be a key to control these factors systematically. [ABSTRACT FROM AUTHOR]

The mixing characteristics of cubic particles in a cylinder mixer are analyzed by the SIPHPM simulation in comparison with spherical particles. The assembly of cubic and spherical particles of uniform size is pre-divided into two parts in the axial, circumferential or radial directions respectively. Then they are mixed when the cylinder is rotated at different rotational speeds of Ω d  = 15–60 rpm. The mixing degree is evaluated by either the Lacey mixing index or the mixing information entropy. A normalized mixing entropy is proposed here to compare the absolute degree of mixing with non-equivalent particle numbers. It is found that, for cubes, the radial mixing efficiency is higher than the circumferential, and the radial and circumferential mixing degrees are both larger than the axial. Compared with spheres, cubic shape may enhance the circumferential mixing whereas reduce the axial mixing levels at high rotating speeds. However, at low rotating speed, cubic shape always reduces the degree of mixing of all the three patterns. Moreover, the axial dispersion characteristics are also explored by the probability density functions and the axial paths. The spatial and temporal diffusion coefficients of concentration and kinetic energies are illustrated and used to explain the axial dispersion mechanism in analogy with diffusion equation. The mean diffusion coefficient of rotational energy is independent of rotating speed, which means the axial diffusion of rotational energy depends on the eccentric feature of cubic particle, i.e. rotational ability. In contrast, it is preferred to regard the axial dispersion mechanism of spheres as convection rather than diffusion. [ABSTRACT FROM AUTHOR]

Powders are commonly used dosage forms for drug delivery through nasal, pulmonary, and oral routes. Recently, bioactive wound powders (BWPs) have attracted considerable attention as wound dressings and drug delivery systems because of their features like high stability, rapid effect, applicability on deep or irregular-shaped wounds, exudate absorption, in-situ hydrogel formation, and no need for dressing change. Medicinal plants, drugs, and animal-derived compounds such as proteins and extra cellular matrices can be formulated to BWPs. Furthermore, various biopolymers can be used to formulate BWPs with desired properties. The increasing number of clinical trials, patents, and marketed products necessitate a review about BWPs. The current review outlines design aspects of BWPs including composition, flowability, fluid uptake, in-situ hydrogel formation, adhesion to wound, and interaction of particles with wound environment, as well as their fabricating techniques, sterilization method, and packaging. Moreover, we highlight commercialized products, ongoing clinical trials, and patents. [Display omitted] [ABSTRACT FROM AUTHOR]

The surfaces of vibrating flip-flow screens have the advantages of high vibration intensity, non-blocking holes, easy depolymerization of clustered particles, and self-cleaning functionality, which are widely used in the classification of wet fine-grained granular materials. Various scholars have studied the screening performance, dynamics, elastic elements, and single-particle motion of vibrating flip-flow screens, however, relatively few studies have been conducted on the movement of particles, the elastic screen surface, and numerical simulation of particles on the elastic screen surface. In this study, the numerical simulation was conducted on the elastic screen surface and movement of particles based on finite element method and discrete element method coupling. The result of on a single elastic screen plate indicated that when the excitation angular frequency of the screen was 70 rad/s, the effect of different sizes of particles' stratification on the screen surface was better. The material on the double vibrating flip-flow screen surface exhibited the vibration excitation "filtering effect" on the screen surface; frequency-doubling signals in the vibration response of the stable, transition, and chaotic zones on the screen surface gradually increased, and the particles displayed stable, wave and chaos motions. With an increase in particle size, the particle velocity increased along the direction of the screen surface while decreasing perpendicular to the direction of the screen surface, and the velocity difference between the 10-, 16-, and 25-mm particles was small. A standard deviation analysis of the velocity value demonstrated that the velocity of 10 mm particles can effectively represent the movement velocity of particles on the screen surface. The velocity values in the x and y directions were 1.0725 m/s and 0.8303 m/s respectively. The feed rate had little influence on the movement velocity of the particles. [Display omitted] • Established a particles motion stratification model and screen simplified model. • The particles movement were divided into stable, transitional, and chaotic region. • The feed rates had a small effect on the velocity of particles movement. • The velocity of 10 mm particles can approximate the particles on the screen. [ABSTRACT FROM AUTHOR]

This model has been developed for transient simulation of clogging (also called as fouling) in submerged entry nozzle (SEN) during continuous casting. Three major steps of the clogging have been taken into account: (a) transport of non-metallic inclusions (NMIs) by turbulent melt flow towards the SEN wall; (b) interactions between melt and wall, and the adhesion of the NMI on the wall; (c) formation and growth of the clog by NMI deposition. The computational domain is divided into bulk and near-wall regions. An Eulerian-Lagrangian approach is employed to calculate the transport of NMIs by the turbulent flow; a stochastic near-wall model is adopted to trace particles in the turbulent boundary layer (near-wall region). The early stage of clogging is modeled by the dynamical change in wall roughness, while the late stage of the clogging is modeled by building a layer of porous clog region from the wall. This layer is called as ‘clog’, and it continues to grow by attaching more NMI particles. To evaluate the model, a laboratory experiment, which was designed to study the clogging of SEN during steel continuous casting, is simulated. It is verified that the model can reproduce the experiment: the calculated clogged section of the nozzle is qualitatively comparable with as-clogged sections in laboratory experiments; the calculated mass flow rate through the nozzle agrees with the experimentally-monitored result as well. New knowledge is obtained. (1) Clogging is a transient process interacting with the melt flow, and it includes the initial coverage of the nozzle wall with deposited particles, the evolution of a bulged clog front, and then the development of a branched structure. (2) Clogging is a stochastic and self-accelerating process. Finally, model capabilities/limitations, uncertainties for choosing the modeling parameters such as mesh size, Lagrangian time scale, the correction factor in the interpolation of clog permeability are studied and discussed. [ABSTRACT FROM AUTHOR]

Hybrid structure significantly affects the collection mechanism and performance of a hybrid particulate collector. The electrostatic precipitation of particles in the wire-perforated plate structure of a full-scale compact hybrid particulate collector is numerically simulated in this study. The distributions of electric and flow fields and the charging, motion, and precipitation of particles in this specific structure are studied. The results show that the distribution of electric field in the final stage is asymmetrical because of the baffle plate at the end of the channel. The field distributions of other stages are identical to that of wire-plate electrostatic precipitator. The openings increase the electric field strength in the region adjacent to the perforated plate. The electric field passes through the openings, which is then distributed to the back side of the perforated plate. The aerosol cross flow rate along the perforated plate varies periodically under the effect of electric body force. Whereas, the overall cross flow rate of each stage is the same, except the first stage. Two counter-rotating eddies are formed behind the perforated plate between every two openings. Particle charge exceeds 80% of the final charge when the particles move to the position of the first wire. The 10 μm particles finish their charging processes faster than 1 μm particles with a final charge of approximately 100 times that of 1 μm particles. The charge acquired by a particle under the wire-perforated plate structure is 3% higher than that under the wire-plate structure. Particle trajectory result shows three modes of electrostatic precipitation in a compact hybrid particulate collector, namely, collection on the front, flank, and back sides of the perforated plate. Particle transport by eddies on the back of the perforated plate plays an important role in particle deposition on the back side. Variation in the capture probability of particles released from different positions corresponds to the opening structure. High and low probability areas separate with each other. The collection efficiency of 10 μm particle is higher than that of the 1 μm particle. The results can explain hybrid mechanism and optimize hybrid structure. [ABSTRACT FROM AUTHOR]

The electrostatic effect can significantly increase filtration efficiency of a fibrous filter. Numerical tools for the performance evaluation or design of electrostatic enhanced filtration system are lacking. This study developed a numerical model to simulate the performance of an electrostatic enhanced filtration system. The model considered all the physical phenomena in a filtration system: the corona discharge, air flow, particle charging, particle motion and filtration. Measured data from previous studies were used for model validation. The validated numerical method was then used to investigate the influence of filter structure parameters on the performance of electrostatic enhanced pleated filter. The filtration efficiency and energy consumption were evaluated. The effects of pleat distance, pleat height, applied voltage, and discharge wire position were examined. The results show that EEAF with shorter pleat distance and greater pleat height has higher efficiency. An increase in applied voltage raises both the efficiency and the electrical energy consumption. Filter performance is also sensitive to discharge wire placement. Overall, the numerical model developed here is a powerful tool for the design of electrostatic enhanced pleated filtration system. [ABSTRACT FROM AUTHOR]

The advanced hybrid particulate collector (AHPC) is a highly promising and novel hybrid electrostatic filter technology that removes particles from flue gas. Perforated plates are used as collecting electrodes to attain better synergism between the electrostatic and bag zones. A laboratory-scale AHPC was built to investigate the dust collection performance of perforated plates with different percentages of open area (POA) and opening types. Particles were deposited on the front, flank, and back sides of the plate. Differences in cake packing density were observed at different locations. With the increase in POA, the collection efficiency of the front side decreases, whereas the collection efficiencies of the flank and back sides increase. The increase in the collection of the flank and back sides compensates for the decrease in the collection of the front side, which only changes slightly the total efficiency with the POA. The opening type exhibits minimal effect on total efficiency. A numerical method was established to simulate the dust collection process in the electrostatic zone. Simulation results indicate that the openings change the electric field near the plate and facilitate particle deposition on the flank and back sides, which result in the characteristics of collection efficiency. The difference in the cake structure results from the distribution of electric field strength on the plate surface. [ABSTRACT FROM AUTHOR]

In several multiphase flow applications such as fluidization, thermal spraying, atomization manufacturing and so on, the Newton's law is widely enacted to formulate the particle/fluid kinematic interaction and then to compute particles kinematics. This paper provides analytical solutions of the Newton's law in its time-dependent formulation or simplified formulation, the latter being a reduction of the time dependent problem into a spatial description of the particle motion. It was found that the velocity solution is strictly similar in both cases so that the simplified formulation is viable. The W_ 1 branch of the Lambert's function yields the analytical particle residence time and the particle velocity which enable to characterize particle kinematics and capabilities of cold spraying. Typical particles residence time is of about 10 − 7 –10 − 6 s and a typical characteristic duration is of about 10 − 4 –10 − 3 s to produce a deposit layer. This explains the high productivity rate of cold spraying among innovative additive manufacturing processes. Theoretical limitations of cold spraying are depicted using analytical solutions. Variances of particles velocity are mapped depending on both particle nature and Mach number used in cold spraying. According to analytical laws, the particle velocity using air propellant gas is limited to 600 m/s–1000 m/s for the situation of low particle density-diameter combination (ρ p⁎ D p ) experienced in cold spraying. Helium increases this kinematic limitation up to 1000 m/s–1600 m/s. Such analytical depictions characterize and facilitate a theoretical selection of process parameters including suitable particle features depending on gas nature and kinematic capabilities of cold spraying. [ABSTRACT FROM AUTHOR]

To study the non-circular effect, the mixing of polygonal particles in a rotating drum is simulated by the soft-sphere imbedded pseudo-hard-particle model (SIPHPM method). Eight particle shapes ( N s = 3–10) are filled in the drum at rotating speeds ( ω = 0.5–3 π /s) respectively. The mixing process, quality, velocity and kinetic energy are analyzed by the mixing index and entropy. A cluster-like upcasting motion is found especially for square particles at the rapidest rotation. The mixing index and entropy show consistent variations of mixing degree. Two mechanisms can affect the mixing entropy, through either the static covering related to shapes or the concentration reduction in rolling/cascading/cataracting process related to the rolling capability. Only the first mechanism affects the mixing index. They are both used to explain the effects of particle shape on mixing from the points of view of overall dispersion uniformity and local concentration. The mixing index indicates higher mixing degree for the square, hexagonal and triangular shapes. Except the triangular and square shapes, other shapes play similar characteristics in the area fractions of the flowing core and static base, as well as the radial distributions of the mean and fluctuation velocities. Under the same rotating speed, the particle kinetic energy increases with N s , which is caused by the reduction of energy dissipation with a better roundness of particle shapes. [ABSTRACT FROM AUTHOR]

High Temperature Gas Cooled Reactors (HTGRs) are fueled with tristructural isotropic (TRISO) coated nuclear fuel particles embedded in a carbon-graphite fuel body. TRISO coatings consist of four layers of pyrolytic carbon and silicon carbide that are deposited on uranium ceramic fuel kernels (350 μm – 500 μm diameters) in a concatenated series of batch depositions. Each layer has dedicated functions such that the finished fuel particle has its own integral containment to minimize and control the release of fission products into the fuel body and reactor core. The TRISO coatings are the primary containment structure in the HTGR reactor and must have very high uniformity and integrity. To ensure high quality TRISO coatings, the four layers are deposited by chemical vapor deposition (CVD) using high purity precursors and are applied in a concatenated succession of batch operations before the finished product is unloaded from the coating furnace. These depositions take place at temperatures ranging from 1230 °C to 1550 °C and use three different gas compositions, while the fuel particle diameters double, their density drops from11.1 g/cm 3 to 3.0 g/cm 3 , and the bed volume increases more than 8-fold. All this is accomplished without the aid of sight ports or internal instrumentation that could cause chemical contamination within the layers or mechanical damage to thin layers in the early stages of each layer deposition. The converging section of the furnace retort was specifically designed to prevent bed stagnation that would lead to unacceptably high defect fractions and facilitate bed circulation to avoid large variability in coating layer dimensions and properties. The gas injection nozzle was designed to protect precursor gases from becoming overheated prior to injection, to induce bed spouting and preclude bed stagnation in the bottom of the retort. Furthermore, the retort and injection nozzle designs minimize buildup of pyrocarbon and silicon carbide on the retort wall and manage nozzle orifice accretions. The equipment and operating methods have yielded very good reliability of equipment and product reproducibility in the TRISO coated particles batches. [ABSTRACT FROM AUTHOR]

Resuspension of spherical particles from a flow-induced fluttering, partially free, flexible substrate was experimentally studied. The effects of the flow-induced flutter on the particle resuspension, and the underlying mechanisms initiating the particle resuspension in the fluttering substrate case, were quantitatively illustrated by comparing with the fixed substrate case. The results show that the flow-induced flutter of the substrate remarkably enhanced the particle resuspension and greatly reduced the threshold velocity. A force caused by the fluttering acceleration of the substrate was identified as an important factor enhancing the particle resuspension. The existence of a significant flutter-induced aerodynamic force/moment enhancement acting on the particles was demonstrated, and it was another necessary factor promoting the particle resuspension. This paper not only reveals the phenomenon of particle resuspension by the flow-induced flutter of the flexible substrate, but also provides useful information for facilitating or preventing the particle resuspension in the industrial and environmental fields. [Display omitted] • Fluttering substrate and particle resuspension were quantified and correlated. • A fluttering substrate enhanced particle resuspension compared with the fixed one. • Particle diameter and position were observed to influence particle resuspension. • A force caused by fluttering acceleration was identified as an important factor. • An aerodynamic force/moment enhancement was another necessary factor. [ABSTRACT FROM AUTHOR]

The motion of spherical particles in liquid phases was investigated using a two-dimensional particle tracking analysis (2D-PTA) method. The analysis of four different materials with this method revealed two different types of particle movements occurring simultaneously: Brownian diffusion and sedimentation. When these two different displacements occurred simultaneously, in the case of particles with a larger size or higher density, the sedimentation displacements were significantly faster than those associated with Brownian diffusion. The occurrence of a faster sedimentation compared to the Brownian diffusion severely affects the accuracy of size determination using PTA methods, as these approaches are based on the Stokes-Einstein relationship, in which the size of a particle is inversely proportional to its Brownian diffusion coefficient. In addition, we successfully demonstrated, for the first time, the potential of the novel PTA method for simultaneously determining the particle size and identifying the constituent material of a limited range of silica and gold particle sizes. The present method may play an important role in the development of new industrial and biological applications of materials. [ABSTRACT FROM AUTHOR]

The mixing characteristics of binary-sized particles in rotating tumbler are studied by discrete element method (DEM). The cases of diameter ratios of R D = 1:1, 2:1 and 3:1 under three rotating velocities ω = 1.0, 2.0, 3.0 π rad/s with or without friction from front and rear walls of the tumbler are simulated. Short and long tumblers ( L = 0.15 and 0.3 m respectively) are used with stationary or rotating end-walls. Considering the local granular concentrations of binary-sized particles, an improved information entropy function is proposed to evaluate the overall mixing degree of particles in the tumbler. Moreover, the kinetic energy and the radial distribution function are also explored to discuss the impacts of friction from front and rear walls, the size ratios and the rotating speeds on particle mixing. All the analytical results indicate that the friction from the stationary front and rear walls play a significant role in degrading the flow regime and suppressing particle mixing especially in short tumblers because of the motion resistance. When the effective contact area for end-walls is larger than the lateral wall, it may be even more important than the rotating speed for determining the mixing degree. The lengthened tumbler may attenuate the effect of end-wall frictions. The size ratios play either a positive or a negative role in influencing particle mixing, caused by the static feature of size difference and the dynamical different property inducing size segregation respectively. In addition, the rotations of end-walls may have an effect of mixing enhancement that is reverse to the stationary end-walls. [ABSTRACT FROM AUTHOR]

The discharge of regular noncircular particles through a hopper orifice is simulated by discrete element method. A novel approach of incorporating distributed sub-spheres around the non-spherical particle borders is developed. The aim of this work is to explore the effect of roundness on the discharge behavior as well as relevant mechanisms of hopper discharge. Seven types of non-spherical particles, i.e. triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal and decagonal shaped particles, are chosen for comparative study. They are respectively discharged freely from the hopper beds of three different base angles, i.e. α = 65, 70 and 75 ° . The discharge process, fraction, flow rate, and voidages are analyzed to show the effect of particle roundness on discharge characteristics. [ABSTRACT FROM AUTHOR]

The electrostatics of electrohydrodynamic atomization (EHDA) process in a shuttle-chamber for polymeric particle fabrication was investigated. The electrical potential field between the spray nozzle and the ground plate inside the chamber was measured three-dimensionally and demonstrated that the electrical field strength increased with decreasing nozzle-plate distance and made more effect on liquid spraying. Four liquids, two inorganic liquids (water, KCl) and two organic liquids (PLGA + DCM ( w / v = 7%), PLGA + acetonitrile ( w / v = 8%)) were tested and the organic liquids were sprayed to fabricate micro-particles. For spraying inorganic liquids the current scaling was I ~ Q 1/2 but for spraying organic liquids the current scaling was I ~ Q 1/4 . The accuracy of current scaling depended on the values of δ μ δ 1/3 , which was independent of the nozzle-plate distances (electric field strength). In addition, the spray current increased with decreasing nozzle-plate distance (or increasing liquid flow rate or liquid conductivity). As a result of spraying polymer solution with volatile organic solvent, particles with size of 0.61– 36.10 μm were fabricated. Particle size decreased with decreasing nozzle-plate distance as well as increasing conductivity of polymer solution or decreasing the liquid flow rate. For all cases of particle fabrication, Rayleigh limit was never reached and no coulomb fission occurred in the experiments. [ABSTRACT FROM AUTHOR]

Particle impaction on a droplet surface directly affects the particle capture by the droplet, and this phenomenon is the basic process of wet scrubbing and wet deposition. The experimental system is established to in-situ observe the behavior of micron particles impacting on the liquid surface. 50–200 μm hydrophobic PMMA and PS particles were used. The particles showed two types of motion behavior, namely, submergence and oscillation, after impaction onto the liquid surface. During particle sinking, the advancing contact angle remained constant. The shape of the liquid surface met the Young–Laplace equation under the quasi-static assumption. After the angle of the three-phase line reached the critical value, the liquid surface was closed, and the particle submerged. A small bubble formed, adhering to the particle trailing surface. If the particle velocity decreases to zero before the angle of the three-phase lines reaches the critical value, the particle will reverse the direction of its motion. When the particle moves to the horizontal liquid surface, the movement ceases. Reciprocating oscillation behavior was not observed. During particle reversion, the receding contact angle gradually decreased and then remained unchanged. The large contact angle hysteresis is the main cause of failure observation in rebound motion mode in the experiment. The changing rule of the critical submergence/oscillation velocity with the particle diameter and surface tension coefficient was studied. As the particle diameter increases, the critical submergence/oscillation velocity decreases. As the surface tension coefficient increases, the critical submergence/oscillation velocity increases. The observed critical submergence/oscillation velocity in this experiment demonstrated the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Recently, scCO 2 (supercritical-carbon-dioxide) used as the green medium in industrial production has attracted much attention of researchers because of its unique physical properties. Aiming at the direct or indirect interaction between scCO 2 and particles, this paper introduces in detail the research status about the combination of scCO 2 and particles to guide industrial production from three aspects. For the performance of transporting particles by scCO 2 in the two-phase flow system of scCO 2 and particles, the effect of scCO 2 flow rate, physical properties of scCO 2 and particles as well as the transporting type are reviewed. As to the heat transfer performance from particles to scCO 2 , the influence of scCO 2 and particles flow rate, physical properties of scCO 2 and particles as well as the contact style between scCO 2 and particles are presented and discussed. For the mass transfer kinetics model between scCO 2 and particles of the supercritical extraction, the governing equations and application occasions of different models are presented. Furthermore, the combination or comparison of various mass transfer kinetics models for the accuracy of predicting extraction performance comparisons among above models are conducted. The full text is mainly based on the theoretical aspect and part on experimental aspect which shows the use of carbon dioxide combined with particles to guide industrial production from the above special point of view [Display omitted] [ABSTRACT FROM AUTHOR]

A DEM study of a rocking particle bed is performed to show the effects of rocking frequency and amplitude on particle discharge. Six rocking frequencies of f r = 0, 0.1, 0.2, 0.3, 0.4, 0.5 Hz with seven rocking amplitudes of θ r = 5°, 15°, 30°, 45°, 60°, 75° are simulated respectively. The particle distributions, discharged fractions, flow rates, particle trajectories and kinetic energies are compared and analyzed in detail to show and explain the features of particle discharging process under different rocking conditions. The rocking frequency is found to be the primary factor to determine the direction of influence on particle discharge, i.e. either beneficial or detrimental, whereas the rocking amplitude is the secondary factor to magnify the primary influence on particle discharge. In addition, the flare angle of the bed can determine the mode of influence on particle discharge, i.e. either a linearly varied discharge or an oscillated variation of discharge. The results are helpful to improve the process control and optimal design of the particle discharge beds in many engineering applications. [ABSTRACT FROM AUTHOR]

Pure Fe 2 O 3 particles were coated with MgO using coprecipitation method under different conditions. For the aim of improving the coating amount and uniformity, the coprecipitation coating method was firstly studied to avoid sticking during fluidized reduction of iron ore. The actual coating amount on the particle surface was quantitatively determined, the sticking problem during fluidizing reduction can be avoided with a MgO coating amount around 0.411 wt.%. The coating amount of MgO on the particle did not decrease after fluidized reduction. Samples were analyzed using (SEM/EDS) analysis, it was found that the MgO coating was effective and intact and merely no exposed part on the Fe 2 O 3 particle surface. The coating uniformity was improved comparing to other coating methods. Precipitates of different crystal structures and morphology generated with different precipitation conditions tend to nucleated at the bottom part of the Fe 2 O 3 particle as the nucleation energy there is lower. [ABSTRACT FROM AUTHOR]

When hydrophobic particles are employed to prepare self-lubricating electroless composite coatings, they usually require surface modification to improve their wettability. The study focuses on the resultant change in wettability of the MoS 2 particles with an inorganic coating. Al 2 O 3 -coated MoS 2 particles were prepared by using a heterogeneous nucleation process. Then, particle surface morphology and structure were examined by using SEM, EDS and XRD. Contact angle measurements were conducted by using a thin layer wicking technique and a sessile drop method in order to determine the surface free energy components of the bare and the coated MoS 2 particles. Our results showed the MoS 2 particles were successfully coated with an Al 2 O 3 layer, which is an amorphous structure. The decreased water contact angle indicates an enhanced hydrophilicity for the coated particles. This decrease depends more strongly on a significant decrease of a new parameter ratio, γ + /γ − , than on a slight increase in total surface free energy. The surface energy component of the bare MoS 2 is very consistent with that of Talc, and that of the Al 2 O 3 -coated one is very similar to that of alumina, apart from the base component. [ABSTRACT FROM AUTHOR]

A novel mechanism for automatic sizing of sago granules is presented in this paper with analytical and experimental studies. This automation method would help to overcome the difficulties faced in the conventional labor which is the intensive process of sago sizing. This paper mainly discusses the data required to define the particle trajectory and behavioral movement in shaping the sago granules. Mathematical models are prepared and experimental studies are performed for the instant at which the flight of particles will occur due to centrifugal flee force and for the trajectory of the particle dynamics for various rotational speeds of the bowl and inclined rod that is coupled to the bowl. The prepared range of inclination angle of the rod is 60° to 64° with the horizontal plane. The maximum flight velocity of particle with a maximum height for models and experiments is 9.81 m/s for the height of 46.43 mm and 9.8 m/s for the height of 43.12 mm. The total residence time of the particle inside the bowl diameter of 200 mm and height 50 mm is also determined numerically as 6 min 43 s and experimentally as 7 min 15 s for the initial radial position of the particle of 20 mm from the axis of rotation of the bowl. The results of analytical models are compared and validated with the experimental results and the analytical results coincide with experimental results with negligible amount of error. [ABSTRACT FROM AUTHOR]

A drag force closure model for particle-laden viscoelastic fluid flows is the key to describing the ensemble-averaged behavior of the mixture. The effects of fluid rheological properties on the flow dynamics of a spherical particle in viscoelastic fluids in the creeping flow regime are parameterized using the Giesekus rheological model. Direct numerical simulations are performed within a large range of Deborah number(0−10).The drag force of a sphere in unbounded Giesekus fluids decreases monotonically with the increase of Deborah number. The negative wake may occur when the viscosity ratio is larger than 0.6 in Giesekus fluids but is absent in Oldroyd-B fluids in all conditions. An explicit closure model for the drag coefficient of a sphere in Giesekus fluids is established using the backpropagation artificial neural network. The drag closure model provides a method for explicitly formulating the momentum exchange model for dilute suspensions of solid particles in shear-thinning viscoelastic fluids. [Display omitted] • The effects of viscoelasticity and shear thinning on the drag force are investigated. • The negative wake downstream of sphere is found and discussed. • The drag force model for Giesekus fluids is established.⊂ [ABSTRACT FROM AUTHOR]

Abstract: Biomass and bed material particles have been found to exhibit significant density differences during the operation of a circulating fluidized bed boiler. Further studies are required to analyze the mixed flow characteristics of these particles in a furnace. We built a test apparatus for a cold-operation, biomass-circulating fluidized bed and designed a space-storage sampler for furnace particle sampling based on modeling theory. The current study found that adding biomass particles nearly did not affect the flow characteristic and distribution of bed material particles because of density difference. However, biomass-particle enrichment phenomenon unexpectedly occurred in the lower furnace region and at the bottom of the top furnace outlet where biomass particle concentration was extremely low. Analyses and observations revealed that downward flow near the wall can effectively carry biomass particles to the bottom of the furnace, thus leading to the enrichment of biomass particles in the lower furnace region. The inhibition mechanism of dense, inert, bed material particles also limited the flow of light biomass particles into the upper furnace region. Different kinds of biomass exhibited similar particle distribution characteristics. Light biomass particles were enriched at the bottom of the furnace, and could hardly reach the furnace outlet. [Copyright &y& Elsevier]

Abstract: A numerical study of gravity-driven monolayer granular flow in a contracted vertical silo is carried out using discrete element method. The bed dimension is 800×2000×12mm in wide, height, and depth directions, respectively, filled with 12,210 spherical granular particles of diameter of 12mm. The particles are loaded onto the bed from nine fixed points equally spaced at the top and discharged from a 120mm wide orifice at the bottom of the bed. By tracking particle trajectories and analyzing them via probability density function, a Gaussian-form dispersion of particles in the horizontal direction is shown. The results are validated by experimental observations. For mechanical analysis, an ideal but general geometrical model of particle dispersion is proposed. It explains the mechanism of Gaussian distribution and the feature of narrow band configuration of particle dispersion successfully. It improves the understanding of particle dispersion characteristics of gravity-driven slow particle flow, and provides a way to estimate the performance of particle-bed reactor. [Copyright &y& Elsevier]

Abstract: Traditional discrete element simulations of particle flows in complex geometries rely on the glued particles approximation of geometrical surface. Our recently developed algorithm, RIGID [9], is more robust and accurate than the glued particle method for detecting interactions of spherical particles with arbitrarily shaped walls. However, RIGID is difficult to implement and can be inefficient in identifying particle–vertex or particle–edge contact. To resolve these problems, an improved version of RIGID (RIGID-II) is proposed in this work, which utilizes the basic features of different contact types. By introducing a treatment list to record identification states, the most time consuming step, identification of particle–vertex (edge) contact, is improved significantly. Moreover, such a list can ensure unique identification of particle–vertex or particle–edge contact. Numerical tests show that RIGID-II can predict all contact states accurately. Moreover, it is much more efficient than RIGID and the glued particle method. [Copyright &y& Elsevier]

Abstract: Using a spherical harmonic series, the three-dimensional shape of star-shaped particles (e.g. most powders, sand, gravel) can be represented mathematically as readily as can a sphere, cube, or ellipsoid. In principle, any particle parameter, such as volume, surface area, moment of inertia tensor, or integrated mean curvature, can be easily computed. In this paper, we extend this list by developing three important algorithms, which have been found useful for regular particles, and adapt them to the case of random star-shaped particles using spherical harmonic series. These three algorithms are: a two-particle contact function, how to add a uniform-thickness shell to a single particle, and estimation of the convexity of a single particle using an algorithm for computing the convex hulls of non-convex particles. A derivation and numerical examples are shown for each algorithm. The two-particle contact function may be used in random particle placement programs, so that random-shaped particles may be used in suspension models as readily as spheres or ellipsoids. New results are shown for how the volume of a uniform-thickness shell, normalized by the surface area of the original particle, depends on the shell thickness t. For a sphere, the exact expression is cubic in t, with the linear coefficient unity and the quadratic coefficient equal to the reciprocal of the sphere radius. For star-shaped particles, the coefficient of the linear term is also unity. For all star-shaped particles considered, the coefficient of the quadratic term in t is approximately equal to the reciprocal of the radius of the volume-equivalent sphere, to within a few percent. The convexity measure, using convex hulls, adds to the list of useful shape parameters for random star-shaped particles and is shown to distinguish between different particle sets. [Copyright &y& Elsevier]

Abstract: We describe a highly efficient method for simulation of particulate materials at the granular level on graphics processing unit (GPU) hardware. Our GPU implementation of a discrete element method (DEM) allows for both rapid visualisation and physically accurate simulation of particulate materials, with a specific focus on sand. Our model represents each granule as a tetrahedral lattice of four particles, thereby implicitly modelling static friction through interlocking of neighbouring granules. Simulations performed with our implementation produce demonstrably realistic granular behaviour with respect to both force characteristics and reactive behaviour of typical sand piles. The implementation is also highly efficient, achieving 256K tetrahedral granules at 120milliseconds per frame of animation, and requires only a personal computer equipped with any recent commodity graphics card to accelerate all simulation physics. Further, our model admits subtle real-time lighting effects, such as particle self-shadowing and shadowing among granules and the environment, important for reproduction of the distinctive appearance of granular materials. Our model also supports interaction with a general environment by first point-sampling objects and then treating these as large “granules.” In this way, our simulation naturally handles arbitrary rigid body interaction, thus making it applicable to broader real-time simulation applications. [Copyright &y& Elsevier]

Abstract: Present work reports on the mass production of high surface area Al2O3 and ZrO2 nanoparticles using inexpensive precursors (aluminium nitrate and zirconium oxy nitrate) developed from natural minerals (bauxite and zircon). Automated hot-air spray pyrolysis has been identified as suitable method for mass production of Al2O3 and ZrO2 nanoparticles with high surface area and free flowing structure. The chemical purity, crystalline phase, size distribution, surface area and morphology of the produced nanoparticles are discussed in detail. Highly spherical cubic Al2O3 nanoparticles with an average particle size of 25nm (d50) and the specific surface area of 336m2g−1 were obtained. Subsequently, highly spherical monoclinic ZrO2 nanoparticles with an average particle size of 30nm (d50) and the specific surface area of 280m2g−1 were obtained with the help of hot-air spray pyrolysis. The present automated experimental design yields 26–28g of Al2O3 nanoparticles for the operation of the system for 8h and yields 32–34g of ZrO2 nanoparticles for operation of the system for 10h. [Copyright &y& Elsevier]

Abstract: The drag force is one major particle–fluid interaction force in multiphase flows. Conventional drag force models do not accurately consider the effect of nonuniform particle distributions which limits their applicability with considerable nonuniform particle distributions. A meshless method (Element-Free Gelerkin method) was used for direct numerical simulations to simulate real particle collisions and investigate the drag coefficient variations in various nonuniform particle distributions. The classical drag force model is corrected using nonuniformity coefficients based on various nonuniform particle distributions in various multiphase flow types. The results show that the nonuniform particle distribution greatly affects the drag coefficient with different compacting directions having different results. In most situations, only the effect of compacting in the direction perpendicular to the main flow direction needs to be considered and the effect of compacting in the main flow direction can be neglected. The particle nonuniformity in the direction perpendicular to the main flow direction reflects the overall dynamic effect of the drag coefficient while the nonuniformity in the main flow direction reflects local fluctuations. Thus, the modified drag force model considering the nonuniform distribution more accurately reflects the dynamic effect of the drag coefficient. It can be more widely used than conventional drag force models. [Copyright &y& Elsevier]

Abstract: A model is developed to predict the evolution of the particle size distribution for batch impact attrition, resulting in a transfer from larger to smaller particles. This model allows the fate of individual particles to be described in terms of impact attrition and the effects of operating parameters, i.e., number of impact cycles, particle velocity upon impact and temperature. The model provides good agreement with experimental results for two limestones striking a target at temperature from 25–580°C and particle impact velocities from 9 to 64m/s with model fitting parameters estimated using nonlinear least squares based on experimental sieve analysis data. The exchange of mass between different particle size intervals is assumed to be first-order with respect to the mass of original particles, proportional to the square of particle velocity, and following an Arrhenius relationship with respect to temperature, but with quite different activation energies for the two limestones. A simplified model with only one fitted parameter provides almost as good agreement as the multi-parameter model and is suggested for practical applications. [ABSTRACT FROM AUTHOR]

Abstract: This work uses the hard-sphere model to simulate the particle motion pattern in a two-dimensional rotating tumbler with a sine-wave boundary. Based on the angular momentum analysis, the present work investigates the intrinsic effects of boundary configuration of tumblers, e.g. the wave number and the boundary amplitude, on the motion pattern of the particles separately. It is found that the particle motion pattern depends on the configuration of the tumbler significantly. There are two collision patterns, namely the primary and secondary patterns. The former pattern dominates when the boundary is composed of low wave numbers or small boundary amplitudes, whereas the latter pattern dominates when the boundary is composed of high wave numbers or large boundary amplitudes. The primary collision pattern is beneficial for the bulk motion of tumbling of the particle clusters, whereas the secondary pattern suppresses it. The interpretation for the different mechanisms of collision pattern indicates the existence of different regions, which is either positive or negative to the tumbling motion. It provides some guiding information for engineering application, such as the design of tumblers for efficient mixing. [Copyright &y& Elsevier]

Abstract: It is deemed substantial that understanding the conceptual differences between the hard-sphere Discrete Particle Model (DPM) and the event-driven Molecular Dynamics (MD) regarding the collision-event handling will help the design of new algorithms to increase the efficiency of collision-handling operations for DPM. The latter has gone largely unrecognized by most of the DPM-based numerical works on fluidization systems. We elaborated these differences and conceptually compared the only two O(1) time complexity algorithms developed for MD and DPM. It was shown that the hash-table strategy that takes into account the main features of fluidization systems increased considerably the efficiency of collision-handling algorithm for DPM. [Copyright &y& Elsevier]