Flow Behavior Of Particles Research Articles

The Influence of Particle Size on Sliding Wear of a Convex Pattern Surface

Sliding wear of bulk handling equipment (e.g., shovel bucket, mill and transfer chute) can be dramatically reduced by using a convex pattern surface compared to a flat surface, by adjusting the flow behavior of particles moving along the convex pattern surface. To study the effect of particle size relative to the dimensions of the convex pattern surface, a coarse graining technique is applied. Comparisons of bulk flow and wear behavior between the convex pattern and flat surfaces illustrate the two-sided effect of the convex pattern surface on sliding wear. The bulk flow behavior indicates that the particle size has a minor effect on the velocity and angular velocity of particles for the flat surface, while it has a significant effect on those of the convex pattern surface. The wear results show that the particle size has negligible influence on the sliding wear of a flat surface and a linear relationship with the sliding wear of the convex pattern surface. The convex pattern surface can reduce the sliding wear through influencing the flow behavior of the bulk material when the equivalent radius of the convex is larger than r50 of particles. This research reveals the relationship between the dimensions of the convex pattern and the particle size on the sliding wear caused by the interaction between bulk material and bulk handling equipment. The relationship should be carefully considered for the applications of the convex pattern surface to bulk handling equipment.

Reliability study of super-ellipsoid DEM in representing the packing structure of blast furnace

In industrial blast furnaces (BFs), the investigations involving the flow behaviors of particles and the resultant burden structure are essential to optimize its operation stability and energy consumption. With the advance of computing capability and mathematical model, the discrete element method (DEM) specialized in characterizing particle behavior has manifested its power in the investigation of BFs. In the framework of DEM, many particle models have been developed, but which model is more suitable for simulating the particle behaviors of BFs remains a question because real particles in BFs have large shape and size dispersity. Among these particle models, the super-ellipsoid model possesses the ability to change shape flexibly. Therefore, the focus of this study is to investigate whether the super-ellipsoid model can meet the requirement of authenticity and accuracy in simulating the behaviors of particles with large shape and size dispersity. To answer this question, a simplified BF charging system composed of a hopper and a storage bin is established. The charging process and the final packing structure are analyzed and compared between experiments and simulations with different shape indexes. The results show that super-ellipsoid particles have prominent advantages over spherical particles in terms of representing the real BF particles, and it can more reasonably reproduce the flow behaviors and packing structure of experimental particles. The computation cost of super-ellipsoid particles is also acceptable for engineering applications. Finally, the micro-scale characteristics of packing structure is analyzed and the single-ring charging process in industry-scale BF using super-ellipsoid particles is conducted.

Effect of outlet characteristics and particle properties on the flow characteristics inside conical hoppers

Precisely predicting the hopper discharge rate and trajectory is of great significance for industrial processing of granular materials. This study uses the DEM (Discrete Element Method)-based open-source software LIGGGHTS to analyze the flow behavior of spherical particles in six cone-shaped hoppers with different outlet shapes (circle, triangle, square, rectangle, pentagon and hexagon) with the various opening area. It was found that the particle flow velocity and mass flow rates are mainly determined by the outlet areas, while the outlet shape have an obvious influence on the particle trajectory which determines the stagnation area in the hopper. The results of the present study can provide meaningful guidance for the optimization of industrial hopper structure design and control.

Micromechanical analysis of roller compaction process with DEM

This study applies the discrete element method (DEM) to the roller compaction process for the analysis of particle flow behavior, porosity distribution in the compaction zone and in the final ribbon, as well as the pressure distribution on rollers. The roller compaction setup was implemented utilizing a piston feeder and smooth roller surfaces. The parameters of the elastoplastic DEM contact model were calibrated by uniaxial compression tests, interparticle and wall shear tests. Finally, the simulation results were validated by micro-computed tomography measurements of porosity profiles of manufactured lactose ribbons. From performed studies, it was observed that the particles passing the smallest gap possess higher velocity than the roller surface, and peak pressure is reached before the smallest gap. Furthermore, due to lateral relaxation, the particles in the center of the ribbon are faster than on the walls. The lateral stress can act as a further possible reason for the transversal ribbon splitting.

Numerical investigation of the influence of particle shape, pretreatment temperature, and coal blending on biochar combustion in a blast furnace

Using carbon-neutral from biomass is a promising solution to achieve carbon neutrality in pulverized coal injection (PCI) technology in an ironmaking blast furnace (BF). In this paper, a 3D CFD model, including the whole region of lance-blowpipe-tuyere-raceway surrounding coke bed, is improved to describe the in-furnace phenomena related to biochar injection under industrial-scale BF conditions. The factors such as particle shape, carbonization temperature, and coal blending are considered to determine the influence on flow and thermochemical behaviors of biochar particles. The results show that, in comparison to spherical particles, the cylindrical particles show a slower gas conversion rate and smaller burnout as a result of the shorter traveling time in the raceway; High carbonization temperature decreases the burnout of biochar in the raceway. From the perspective of the economy, BC-773 has an appropriate ratio of volatile matter (VM) to fixed carbon, which burns more fully and releases a large amount of heat in a limited time, and has the potential to better replace PCI coals in BF practice. The overall gas temperature and burnout of the biochar/coal blend show a non-additivity, indicating there is a synergistic effect during the co-combustion process. This model provides an effective way for understanding and optimizing biomass injection technology in BF practice.

Analysis of flow behavior of cohesive monosized spherical and non-spherical particles in screw feeder

Screw feeders are extensively used in agriculture and processing industries to transport bulk material at relatively controlled rate. The flow behavior can be affected by present moisture content as well as by shape and size of particles which tend to cause bridging or arching of material. In this work, the cohesion between mono-sized spherical particles (due to moisture content), is simulated parametrically by means of cohesion energy density parameter. The correlation acts as an additional normal force to Hertz elastic theory to maintain the contact between two particles. Further, the work is extended by comparing the flow behavior of spherical with non-spherical particles by introducing the non-sphericity (cylindrical shape) using superquadric approach. The superquadric DEM simulation has shown good agreement with our experimental studies for model validation. The simulations quantify the screw feeder performance in terms of average particle speeds (radial, swirl and axial) and contact forces (normal and tangential) by varying screw rotational speed, flight pitch ratio and particle feedrate. The average radial and swirl speeds have shown opposite variation for bigger particle size with increasing cohesion energy density for all three varying conditions. The contact forces between particles also increases with increasing cohesion energy density. The quantitative results depict the same behavior for non-spherical particles as for spherical particles, but with lower magnitude for average particle speed as well as for contact forces.

Directed energy deposition of metal matrix composites: Computational and experimental comparison of powder particle flow behavior

Directed energy deposition (DED) additive manufacturing of metal matrix composites (MMC) involves a mixture of metal and ceramic particles with a range of sizes, morphologies, and densities. Such a heterogeneous mixture of physical characteristics makes it difficult to establish optimum deposition conditions, and hence extensive parametric experiments are often needed to optimize the microstructure and performance of a final component. To provide insight into the behavior of metal and ceramic powders during DED, we report on a study that uses two complementary approaches. First, we formulate a 3-dimensional COMSOL numerical model to simulate the particle trajectories under the influence of gas flow, particle-gas interactions and particle-wall collisions. Second, we implement high-speed photography to examine and compare the powder flow behavior of metallic particles (Inconel 718) and ceramic particles (TiC). Our results reveal that there are distinct differences in particle velocity and spatial distribution between the Inconel 718 and TiC particles, due to the dissimilar particle sizes, morphologies, material densities, and particle collision behavior. By understanding these differences, as presented here, targeted compositions and homogeneous reinforcement distribution can be attained in DED components through proper material and process parameter selection; furthermore, the custom design of tailored microstructures for heterogenous functionality can also be achieved.

Three-dimensional DEM simulation of polydisperse particle flow in rolling mode rotating drum

The flow behavior of polydisperse particles in rolling mode rotating drum is important in industry, but it is still not clear. In this work, the discrete element method (DEM) is used to explore the flow of particles in the three-dimensional drum. After the accuracy of simulation verified by the experimental data from literature, the particle bed is divided into active layer and passive layer. The flow behavior of polydisperse particles was revealed by studying the particle velocity, residence time, mixing and axial dispersion in different regions in the drum. By exploring the parameters such as rotation speed, filling level and the shape and position of the lifter, some ideas are provided for improving the performance of the rolling mode rotating drum. In addition, the difference of flow behavior between polydisperse particles and monodisperse particles is also given, which can provide some reference for the industrial application of complex particle system.

Numerical simulation of the flow behavior and powder spreading mechanism in powder bed-based additive manufacturing

The flow behavior of the powder layer significantly affects subsequent dynamic behavior and final quality of the parts fabricated via powder bed-based additive manufacturing. High powder layer quality is the key scientific problem and technical difficulty, however, the dynamic flow behavior of powder particles and its relationship between powder layer quality were not well understood. In this paper, the influences of typical factors including process parameters (relative layer height and blade velocity) and powder properties (particle size and surface energy coefficient) on powder layer quality of polyamide 6 were systematically investigated by discrete element method to understand the mechanism of the powder layer packing behavior at the particle scale. The packing density, structure uniformity, normalized layer thickness, and surface uniformity were introduced to quantitatively characterize the powder layer quality. The mechanisms at the particle scale, including the blocking of particle, force arch, particle velocity distribution, and cohesion effect were discussed in detail. The results showed that a decreasing value particle size/layer height can effectively weaken the blocking effect of particles, improving the continuity and stability of powder flow and inducing a dense and uniform powder layer. The particles with high average velocity in the gap between the blade and baseplate will move forward after the blade leaves, significantly reducing the layer thickness and packing density. Meanwhile, the cohesion force was determined by the particle size and surface energy coefficient, and the cohesion effect dominated the flow behavior of the particles with a small particle size d = 10μm or a large surface energy coefficient γ = 0.2mJ/m2. These findings can provide useful guidance in understanding the flow behavior at the particle scale and improving the powder layer quality.

Fluctuation of particles during funnel flow discharge from flat‐bottomed silos

AbstractAlthough resonant motion of particles during mass flow discharge from silos has been extensively investigated by earlier researchers, the appearance of such phenomenon during funnel flow discharge has not been emphasized. In this work, the flow behavior of particles during funnel flow discharge from flat‐bottomed silos has been investigated by conducting three‐dimensional Discrete Element Method (DEM) simulations. It is found that particles in the upper part of flowing zone move collectively, manifested by the oscillatory fluctuations of the velocity and the non‐Gaussian characteristics of the fluctuations of individual velocity around the average. Correlation analysis and discrete Fourier transform have been performed to characterize the emission and propagation of velocity fluctuation. It is found that the observed resonant motion of particles is induced by the regular fluctuation of contact force between particles, and there exists an intermediate region in the converging part of the flowing zone. The bottom boundary of this region corresponds to the emission source from which the velocity wave propagates upward and downward. Its upper boundary coincides with that of the converging part of the flowing zone and is featured by the most violent fluctuation of contact force. The simulation results thus suggest that the discharge of granular assembly seems to be determined by the rheological behavior of particles in this intermediate region.

Comparison of roller-spreading and blade-spreading processes in powder-bed additive manufacturing by DEM simulations

The roller-spreading and blade-spreading are main powder spreading methods in powder-bed additive manufacturing. The discrete element method was introduced to simulate nylon powder spreading by both roller and blade spreaders. The two spreading processes were compared from several aspects including particle flow behavior, particle contact forces, forces exerted on spreaders, particle segregation and powder layer density. It is found that powder spreading methods mainly affect the movement trajectory of particles, particle contact forces and forces exerted on spreaders. Complicated dispersion and circulation movement of particles occur inside the powder pile by roller-spreading, while particles have relatively weak dispersion by the blade-spreading. The normal force applied to the roller introduces a compacting effect on the powder pile and creates strong force chains that distribute uniformly in the powder pile. Therefore, the powder bed with higher density can be obtained by roller-spreading in thicker powder layer due to the compacting effect. The blade spreader sustains tangential force mainly, so the blade-spreading process limits its application to thicker powder layer. As the powder layer thickness increases, the roller-spreading is more sensitive to segregation index than that of the blade-spreading. The comprehensive comparison of two spreading processes provides criteria for selecting spreading methods.

Sedimentation effects on particle position and inertial deposition in 90° circular bends

Laminar fluid-particle flows in bend geometries are present in many industrial, pharmaceutical, and biomedical applications. Particle deposition has been studied extensively; however, little attention has been paid to the effect of particle sedimentation on particle position and deposition in different pipe geometry combinations. This study presented a comprehensive analysis of sedimentation effects on particle flow behaviour in 90° circular pipe bends of micron particles in laminar pipe flows. Pipe geometry combinations consisted of eight pipe diameters, nine bend radii, and 30 particle diameters in a range of 1 to 100 μm. The results demonstrated the locations of particles that sedimented to the bottom half of the straight pipe section, and the particle positions upstream from the pipe bend entrance, which was no longer in a fully developed profile. These new locations represent the effects of gravity, pulling the particles down. While obtaining these positions can be found through CFD analysis, we proposed an analytical solution to predict the particle trajectory from different release locations that would help to identify the initial particle distribution at locations upstream to the bend, to obviate the need for long upstream straight pipe sections in the CFD analysis.

EDEM Investigation and Experimental Evaluation of Abrasive Wear Resistance Performance of Bionic Micro-Thorn and Convex Hull Geometrically Coupled Structured Surface

Procambarus clarkii was found to have excellent anti-wear performance against abrasive materials. To improve the wear resistance performance of the soil-engaging component of agricultural machinery, in this study, the micro-thorn and convex hull coupled geometrical structured surfaces inspired from the cephalothorax exoskeleton of the Procambarus clarkii was selected as the bionic prototype. By adopting bionic engineering techniques, three types of novel geometrical structured surfaces were proposed, which were bionic single, double and triple micro-thorn coupled convex hull surfaces (Bionic Type 2, 3 and 4, respectively). The anti-abrasive wear properties of these proposed geometrical surfaces were compared with a conventional bionic convex hull structured surface (Bionic Type 1) and a surface without any structures (smooth). Abrasive wear tests were conducted by using a rotational abrasive wear testing system. The accumulative test time was 80 h and the total wear distance was 6.09 × 105 m. By adopting the EDEM software (discrete element modeling), the Archard Wear model was selected to simulate the wear behavior of five different surfaces. In addition, the wear mechanisms of different surfaces were investigated. The results showed that the smooth surface suffered the most severe abrasive were, the abrasion loss reached 194.1 mg. The anti-abrasive properties of bionic geometric structured non-smooth surfaces were greatly improved; the reduction in terms of abrasion losses ranged between 20.4% and 94.1%, as compared with the smooth surface. The wear resistance property of micro-thorn and convex hull coupled structured surfaces were greatly improved as compared with convex hull and smooth surface. Bionic Type 3 was found to have the best anti-abrasive wear property: the abrasion loss was 11.5 mg. The wear morphology was observed by a scanning electron microscope. Smooth surface was characterized with wide, large size of grinding debris, while the bionic non-smooth surface featured narrow and small size abrasive dust. The results obtained from EDEM simulation agreed well with those of the aforementioned real scenario tests. It was revealed that the wear areas of the micro-thorn and convex hull coupled structured surface were mainly concentrated on the edge of convex hull and micro-thorn that faced the coming direction of particle flow. The geometric structure of the convex hull had beneficial effects on changing the movement behavior of particles, which means the stream of particle flow could be altered from a sliding to rolling state. Consequently, the ploughing and cutting phenomena of particles that act on the surfaces were greatly mitigated. Moreover, after being coupled with micro-thorns, the anti-abrasive wear preparty of the bionic convex hull geometrical structured surface was further improved. The rebound angle of particle flow that contacted the bionic micro-thorn coupled convex hull structured surface was greater than that of the conventional convex hull surface. Therefore, the dispersion effect of particle flow was further enhanced, since the movement behavior of the subsequent impact particle flow was altered. As a result, the wear of the bionic non-smooth surface was further reduced. This biconically inspired novel micro-thorn and convex hull coupled structured surface could provide theatrical and technical references to enhance the wear resistance performance of the soil-engaging component of agricultural machinery and mitigate the problem of abrasive wear failure.

Hydrodynamics of wet particles in liquid-solid fluidized beds using kinetic theory of rough spheres model

To actually describe the flow behaviors of particles in the liquid-solid fluidized bed, the effects of liquid film covered on the particles surface and the sphericity of particles need to be considered for quasi-spherical wet particles. Liquid-solid fluidization characteristics are predicted using a two-fluid model incorporating with the kinetic theory of rough spheres (KTRS) model. Simulation results show that the normal restitution coefficient for wet particles covered liquid film increases with an increase of the particles diameter. As for the sphericity of particles, a higher sphericity of particles gives rise to a lower granular temperature and higher solids pressure and viscosity. Also, the normal restitution coefficient of quasi-spherical particles is relatively small, compared with completely sphere. The simulation results obtained by the kinetic theory of rough spheres model for quasi-spherical wet particles are in satisfactory agreement with the experimental data from Lu et al.

DEM investigation on conveying of non-spherical particles in a screw conveyor

Screw conveyors are extensively used in modern industry such as metallurgy, architecture and pharmaceutical due to their high-efficiency in the transportation of granular materials. And substantial efforts have been devoted to the study of the screw conveyors. Numerical method is an effective way to study screw conveyor. However, previous studies have mainly focused in the regime of spherical particles while the in-depth investigations for non-spherical particles that should be the most encountered in practical applications are still limited. In view of the above situations, discrete element method (DEM), which has been widely accepted in simulating the discrete systems, is utilized to investigate the conveying process of non-spherical particles in a horizontal screw conveyor, with particles being modeled by super-ellipsoids. In addition, a wear model called SIEM (Shear Impact Energy Model) is incorporated into DEM to predict the wear of screw conveyor. The DEM simulation results demonstrate that the particle shape is influential for the flow behaviors of particles and the wear of conveyor. The conveying performance evaluated quantitatively of both mass flow rate and power consumption is subsequently obtained to investigate the effect of sphericity of particle with different operation parameters. Moreover, particle collision frequency and collision energy consumption are acquired to investigate the possible particle breakage between particles and screw blade. The comparisons between particle–particle collision and particle–wall collision reveal that particles with large shape index have more possibility to be damaged in particle–wall impingement.

Study on Convective Flow Behaviors of Phosphor Particles During Curing Process of Silicone and the Influences on the Optical Performance of White LEDs

The correlated color temperature (CCT) variation of the phosphor-converted light-emitting diodes (LEDs) after curing is a common phenomenon. In the past, it was believed that the phenomenon was caused by the sedimentation of phosphor particles. However, not only sedimentation, but these particles can also flow with the natural convection of silicone because of nonuniform heating during curing. The convective flow of the phosphor particles during curing was studied in detail in this work. The CCT variation and phosphor particles flow in the LED device cup with different depths and wall inclination angles were studied. The results show that the CCT increases after curing when the depth of the device cup is shallow. The case is the opposite when the depth of the device cup is deep. The convective flow behaviors of the silicone were revealed in the simulation. The large-angle inclined wall can increase the silicone flow path length and inhibit the particles flow downward caused by the flow to a certain extent. It is envisioned that the findings will strengthen the understanding of the CCT variation phenomenon and guide the encapsulation structure design of LEDs for better color quality.

Analysis of the formation mechanism of coarse-dense structure of silver paste in die bonding

The flow behavior of silver paste during die bonding was analyzed by numerical simulation to clarify the formation mechanism of coarse-dense inhomogeneous distribution of silver particles in a die-attach layer. Depending on the loading speed of a die, silver particles in the paste flow and form a coarse-dense distribution under a die. The microstructure of the paste before sintering was observed by X-ray computer tomography (X-ray CT) and Scanning Electron Microscope (SEM). At a slow loading speed of 1.0 μm/s, the paste is densely packed with silver particles along the diagonal of the die. A coarse structure was observed in the other area of the paste. On the other hand, at a high loading speed of 60.0 μm/s, there was no clear segregation and the paste layer has an almost uniform structure. The SPH method was used to calculate the flow behavior of particles in the paste, and the flow velocity and shear stress of the paste were calculated. The paste velocity and shear stress in the region along the diagonal of the die is smaller than those in other area of the die. A comparison of the shear stress applied to the paste at different loading speeds showed that the smaller the loading speed, the larger the value of summation of shear stress. The difference between the maximum and minimum shear stress in a lateral direction through the center of the die increases with decreasing of loading speed. Thus, a large difference in local shear stress acting on the paste causes the formation of coarse-dense structure of the silver paste. It was found that it is necessary to eliminate local differences in the shear stress acting on the paste in order to achieve uniform joint the silver paste to the substrate without forming a coarse-dense structure.

Rheological and Nutritional Characterization of Sweet Corn By-Product (Cob) to Develop a Functional Ingredient Applied in Dressings.

In this study, a flour from corn cob (central core of the maize ear, stage R4) was obtained through three treatments. The three flours obtained were characterized by bromatological analysis, yield, and granulometry. Additional dressing-type oil in water (O/W) emulsions were developed, varying the formulation by incorporating distinct amounts of corn cob flour. The formulations' stability was evaluated over a period of 21 days, determining the particle size, creaming index, coalescence rate, consistency coefficient (k), and flow behavior indices (n). Results have shown significant differences in protein, fat, and carbohydrate content in the flour, depending on the cooking treatment. A good percentage of grinding yield was obtained (98%), in addition to several fractions by granulometry (60, 120, 250 MESH), showing differences in their nutritional content. Finally, the particle size of O/W emulsions developed varied among formulations. The combination of 0.6% of xanthan gum (XG) and corn cob flour showed major stability in average droplet size. No significant differences were observed in the coalescence rate values for the three formulations. Still, significant differences in the creaming index were evidenced in those formulations without XG or corn cob flour. The results regarding the consistency coefficient (k) and flow behavior indices (n) suggest a possible synergy between XG and flour of corn cob for enhancing the viscosity and pseudoplasticity of dressings in a concentration-dependent manner.

Pore-Scale Simulation of Particle Flooding for Enhancing Oil Recovery

The particles, water and oil three-phase flow behaviors at the pore scale is significant to clarify the dynamic mechanism in the particle flooding process. In this work, a newly developed direct numerical simulation techniques, i.e., VOF-FDM-DEM method is employed to perform the simulation of several different particle flooding processes after water flooding, which are carried out with a porous structure obtained by CT scanning of a real rock. The study on the distribution of remaining oil and the displacement process of viscoelastic particles shows that the capillary barrier near the location with the abrupt change of pore radius is the main reason for the formation of remaining oil. There is a dynamic threshold in the process of producing remaining oil. Only when the displacement force exceeds this threshold, the remaining oil can be produced. The flow behavior of particle–oil–water under three different flooding modes, i.e., continuous injection, alternate injection and slug injection, is studied. It is found that the particle size and the injection mode have an important influence on the fluid flow. On this basis, the flow behavior, pressure characteristics and recovery efficiency of the three injection modes are compared. It is found that by injecting two kinds of fluids with different resistance increasing ability into the pores, they can enter into different pore channels, resulting in the imbalance of the force on the remaining oil interface and formation of different resistance between the channels, which can realize the rapid recovery of the remaining oil.

Production and characterization of Ti6Al4V/CaP nanocomposite powder for powder-based additive manufacturing systems

Ti64/CaP nanocomposite powder was fabricated and characterized for use in powder-bed 3D printing. The microstructure and phase composition, morphology, particle size distribution, sphericity, flow behavior and dispersion of the as-fabricated particles on the building plate of the 3D printer were investigated. The results confirmed a uniform distribution of nanostructured calcium phosphate particles on the surface of primary Ti64 ones. Calcium phosphate appears as an octa-calcium phosphate phase. The morphology of the particles was shown as spherical, and their sphericity was better than the as-received Ti64 particles. The particle size distribution of nanocomposite powder indicated a smaller amount than the as-received Ti64 particles. Additionally, the flow behavior was improved compared to the as-received Ti64 and delivered an optimal dispersion on the building platform. Ultimately, Ti64/CaP nanocomposite powder has a very homogeneous and uniform microstructure and bears a proper flow behavior for use in powder-bed additive manufacturing machines.