Flow Behavior Of Particles Research Articles

Axial segregation characteristics and size-induced flow behavior of particles in a novel rotary drum with curved sidewalls

Particle mixing and segregation are common phenomena in rotary drums, which are challenging to be controlled and driven artificially in powder technology. In this work, the discrete element method (DEM) was applied to construct the novel rotary drum composed of different shaped curved sidewalls. By varying the operation parameters of particle and sidewall shapes as well as the length-to-diameter (L/D) ratio of drums, the axial mixing and segregation processes of binary size-induced particles were investigated. The results show that the axial flow velocity of the particle mixtures is noticeably weakened once the particle angularity increases, making the non-spherical particles to mix better in rotary drums compared to the spherical particles. Besides, in the short drums with size-induced spherical particles, the axial segregation characteristics are significantly enhanced by the convex sidewalls while suppressed by the concave sidewalls. However, for size-induced non-spherical particles, the axial segregation structure can be present in rotary drums with plane and concave sidewalls while not in drums with convex sidewalls. Moreover, the axial segregation band structure of spherical particles eventually increases proportionally with the increased drum L/D ratios. In contrast, the non-spherical particles cannot form obvious multi-proportional segregation bands.

Effect of lifter shape and operating parameters on the flow of materials in a pilot rotary kiln: Part IV. Improvement of the hydrodynamics-related dimensionless correlations

Non-spherical particles are widely processed in industrial-scale rotary kilns. There is nonetheless a lack of simple tools that make it possible to predict their hydrodynamic behavior inside rotary kilns. This article thus focuses on the hydrodynamics of crozets flowing inside a pilot-scale rotary kiln. Thirty-eight experiments were conducted with this product. Experimental Residence Time Distribution curves were successfully obtained with a tracer pulse methodology using painted crozets. Both the experimental mean residence time and the axial dispersion coefficient were obtained by fitting the analytical expression of E(t) for the open-open boundary condition with the experimental E(t) curves. The hydrodynamic behavior observed was qualitatively in agreement with the literature. Our dimensionless models were then re-identified with all of the experimental data and simplified through statistical analysis. This study provides more robust dimensionless hydrodynamic models that can be used to reliably predict the behavior of non-spherical particle flow inside an industrial kiln.

Influence of Wall Angle of Direct Reduction Shaft Furnace on Particle Flow Pattern by DEM Modeling

The shape of shaft furnace is a crucial feature of direct reduction processes, as it affects both particle and gas flow during production. However, current knowledge on the impact of furnace shape on particle flow is limited. Herein, the discrete element method is employed for numerical simulations, in which two different methods of varying the wall angle (i.e., changing the radius or the height) are utilized to investigate the effect of wall angle on the flow behavior of particles in a shaft furnace. The effect of wall angle under different combinations of radius and height on the transformation of the particle flow pattern is innovatively examined, compared to previous studies on charging particles and internal furnace conditions. It is demonstrated in the results that the wall angle of the shaft furnace has a significant influence on the transformation of particle flow mode, with a reduction in the wall angle facilitating the transformation of particle flow mode to mass flow. Furthermore, it is shown in the study that different methods of changing the wall angle have varying effects on the transformation of particle flow mode.

Micro-scale reconstruction and CFD-DEM simulation of proppant-laden flow in hydraulic fractures

A comprehensive investigation of the dynamical characteristics of proppant-laden flow systems in hydraulic fractures is important for the development of unconventional oil and gas resources. In this paper, we combine the micro-scale reconstruction technique and CFD-DEM method to numerically investigate the mobility and distribution rules of proppant-laden fluid in rough hydraulic fractures. To characterize realistic fracture surface morphology, six synthetic fracture models were assembled based on optical scanning data of real shale from three sets of hydraulic fracturing experiments. In order to accurately simulate the fluid-particle two-phase flow in rough fractures, the lift forces and particle rolling effect are considered in the CFD-DEM model. First, the effectiveness of the used CFD-DEM solver was validated by comparing it to the experimental data. We then examined mechanisms for the typical flow behaviors of proppant particles and fracturing fluid in smooth and rough fractures. Subsequently, the surface area ratio of the synthetic fracture model is adopted to characterize the cross-scale relationship between the micro-scale proppant distribution and fracture’s geometric features induced by the macroscale fracturing parameters (i.e., confining stress, fluid viscosity, flow rate, and sand ratio). Lastly, the parameter effects of the fracturing fluid, proppant particle, and fracture aperture on the dynamic characteristics of particulate flow in the hydraulic fracture are further discussed. In summary, the presented numerical model and findings can help better understand particle transport and distribution in real rock fractures and bridge the connectivity of the micro-scale particle flow and macroscopic fracturing parameter, which is vital for hydraulic fracturing process optimization.

Coupled smoothed particle hydrodynamics and discrete element method for simulating coarse food particles in a non-Newtonian conveying fluid

A Lagrangian particle-based numerical framework based on smoothed particle hydrodynamics (SPH) coupled with a discrete element method (DEM) was used to simulate the flow behavior of coarse food particles in a non-Newtonian conveying fluid in a horizontal pipe. Nearly neutrally buoyant nearly spherical calcium-alginate particles were used as model food particles. The capability of the SPH–DEM methodology was successfully validated in non-Newtonian single-phase as well as in two-phase particle–liquid flows by comparing the local phase velocity flow field, radial particle distribution, and particle passage times with experimental Lagrangian measurements obtained by a technique of positron emission particle tracking. The simulations also yielded accurate predictions of flow pressure drop. In addition, detailed information was afforded on local particle spin, fluid pressure, and carrier fluid vorticity. The results demonstrate the high capability of the proposed numerical framework to predict the complex features of complex particle–liquid flows in pipes.

Simulation study on the flow behavior of wet particles in the power-law liquid-solid fluidized bed

Simulation study on the flow behavior of wet particles in the power-law liquid-solid fluidized bed

Semiempirical Model of the Drag Force Acting on an Obstacle in Downward Dense Particle Flows as per the Flow-Around Behavior

Determination of the flow-around drag force acting on an internal when particles downwardly flow around the internal is important for the safety of internals in the downward particle flow channel. In this study, the flow behaviors of particles downwardly flowing around different obstacles were investigated and a semiempirical drag force model was proposed based on the characteristics of the flow patterns. The proposed model was validated and key coefficients were correlated using the experimental data. The results indicate that there were three featured flow zones when particles downwardly flowed around an obstacle: the flow stagnant zone (disappear for triangular/conical obstacle), the slip-shear flow zone, and the flow separation zone. The stagnant zone angle and the flow separation angle were proposed to depict transition points of three flow zones when particles flowed around a cylindrical/spherical obstacle, and the two angles were found independent of the flow condition. A drag force model as per the flow patterns was proposed. The model decomposed the drag force into the compression force, the shear force, and the confinement force. The expressions of the compression stress, the shear stress, the effective area, and the confinement force were given. The mathematical form of the proposed model was validated and key coefficients in this model were also correlated using the experimental data. The average error of the drag force model was ±7.6% while the maximum error was within ±15%.

Influence of Material Characteristics of Hoppers on Particle Flow Behavior

In the previous study, different structures of hoppers were proposed. And the dust suppression performance of hoppers were evaluated. In this paper, different materials of hoppers were selected.And influence of different material on particle behaviors were studied based on the discrete element method (DEM). Results shows that the wall material with low collision recovery coefficient for the hopper has positive effect on suppressing dust diffusion.and the wall material with high static friction coefficient showed little effect on the particle flow state through the hopper.

Experimental Platform Design for Particle Behavior Investigation

The hopper is a kind of important equipment in bulk handling process. In this paper, an experimental platform was designed. The experimental platform was mainly composed of a feeding head, a vertical conveying screw machine, a horizontal conveying screw and a lifting device, a supporting structure, the visual experimental system,the electrical system and the acquisition system. the particle behavior for hoppers can be assessed by the experimental platform. And the visual experimental system will help to investigate the real particle flow behavior and will provide instructions for hopper design in future

Influence of Lump Ore Ratio and Shapes on the Particle Flow Behavior Inside the Direct Reduction Shaft Furnace by Discrete Element Modeling Model

In recent years, with the attention given to hydrogen reduction‐related technologies, the parameter indicators of direct reduction in the shaft furnace have gained importance. Herein, the numerical simulation of the particle flow field in the shaft furnace is investigated with the help of discrete element method (DEM) model. In contrast to the subregional modeling and the single particle shape study of the previous studies, this study innovatively uses the real shape of the particles and the overall structure of the vertical furnace for modeling. The transient characteristics of solid particle flow under ten lump ore ratios and three shapes are considered. The results show that the mass fraction and the shape of lump ore have little effect on the particle falling speed, but have a significant effect on the particle segregation behavior. In addition, the void ratio responds to the permeability condition in the furnace, which is also influenced by the lump ore proportion and shape.

Effect of Moisture and Feedstock Variability on the Rheological Behavior of Corn Stover Particles

Continuous feeding, processing, and handling of biomass powders is pivotal to the economic viability of integrated biorefineries. However, current challenges associated with the operational reliability of bulk solids handling and transport greatly impact the process economics and ultimately the widespread commercialization of integrated biorefineries. In this work, we examine the effect of moisture and feedstock variability on the flow behavior of corn stover biomass particles. The total flow energy, compressibility, shear properties, and wall friction angles were measured for corn stover samples A and B containing 0%, 15%, 25%, 50%, and 75% (mass fraction) moisture contents using a FT4 powder rheometer. In general, the flowability of both A and B was reduced when moisture was present as indicated by the stability and variable flow rate, compressibility, and shear tests. The 15% moisture sample had the highest flow energy, revealing the interplay between the increased surface tension and looser packing both of which were caused by liquid bridging. The 75% moisture sample had the highest compressibility and the lowest flowability factor (ffc). The trend in wall friction angle was found to be dependent upon the surface hydrophobicity of the wall material. The wall friction angle on the hydrophilic, stainless-steel surface increased with moisture and therefore poses additional handling challenges. On the other hand, the wall friction angle on the hydrophobic polymer surfaces were the lowest for samples with intermediate moisture contents. Sample B had greater bulk density, smaller compressibility, and greater flowability than the sample A, as suggested by the compressibility and shear tests. The wall friction angle of sample B was higher than or equal to that of sample A depending on both the type and the surface roughness of the wall material.

Elasto-plastic and adhesive contact: An improved linear model and its application

An improved linear model is developed for elasto-plastic and adhesive contact. New correlations are proposed and validated to estimate the key parameters of the model, including contact stiffness, yield point, maximum pull-off force and time step. The newly proposed contact model is applied to the analysis of single particle contact behaviour upon impact and bulk particle flow behaviour by DEM simulations. The results show that both single particle and bulk powder behave more “cohesively” if contact plastic deformation is considered. A cohesion yield number is proposed to describe the extent of yielding when cohesive particles are in contact with each other. There is a critical particle size, below which the effect of plastic deformation becomes prominent and must be considered. This provides a new framework and criteria for elasto-plastic and adhesive contact model, and a step towards understanding the effect of plastic deformation on the behaviour of cohesive particles.

Digitalized turbulent behaviors of air and rice husk flow in a vertical suspension furnace from computational fluid dynamics simulation

AbstractThe knowledge of fluid–particle flow behavior is necessary. Unfortunately, computational fluid dynamics (CFD) studies are mostly focused on developing numerical methods in detail. Instead, the CFD studies should also subtly shift to become a tool for digitalizing fluid science to guide the practical industrial aspects. Therefore, this simulation study intends to reveal the air and rice husk flow behaviors in a vertical suspension furnace, complete with presenting digital simulation data, aiming to alleviate the escape particle amount. According to this study, the escaped particle amount was suppressed under more sphere particle, smaller particle size, and feed inlet pipe that sunk into the burner. The properties change from rice husk to ash, along with temperature escalation (as in combustion phenomena), enlarging the escaped particle amount, so the cyclone should be installed to handle it. In addition, the results of digital turbulent data from CFD simulation have succeeded in intriguing and revealing the fluid–particle flow behavior in the vertical suspension furnace. The data show a close match to the real phenomena occurring inside this furnace which reflects the standard k–ε model can conclusively predict fluid–particle flow behavior without conflicting Newton's second law of particle motion.

Simulation investigation of the particle flow behavior in the gas full circulation oil shale retort

3D models of the 300 t/d Gas Full Circulation Retort are developed to investigate the flow behavior of oil shale particles in the retorting process using the discrete element method (DEM). The results show that the flow patterns of oil shale particles gradually change from horizontal to waved along the radius direction in the descending process due to the friction between particles and walls. The cumulative contact energies are mainly concentrated at the top of the center pillar and the bottom half of the three support structures. With the addition of the conical structure for gas-oil mixture gathering and the triangular structures for particle distribution, the oil shale particles distribute more uniformly in the retorting zones. The interaction force among particles decreases obviously under those added structures, which is conducive to the enhancing of the convective heat transfer between gas heat carrier and particles. And the cumulative contact energies on the center pillar and three support structures decrease obviously, which could decrease the abrasion of refractory brick structures of the retort.

DEM simulation of particle flow and separation in a vibrating flip-flow screen

Vibrating flip-flow screens (VFFS) with stretchable polyurethane sieve mats have been widely used in screening fine-grained materials in recent years. In this work, the discrete element method (DEM) is used to study the screening process in VFFS to explain particle flow and separation behavior at the particle scale. Unlike traditional vibrating screens, for VFFS, the amplitude response of each point on the elastic sieve mat is different everywhere. This study measures the kinematics of the elastic sieve mat under different conditions such as different stretched lengths and material loads. To establish the elastic sieve mat model in a DEM simulation, the continuous elastic sieve mat is discretized into multiple units, and the displacement signal of each unit tested is analyzed by Fourier series. The Fourier series analysis results of each unit are used as the setting parameters for motion. In this way, the movement of the elastic sieve mat is approximately simulated, and a DEM model of VFFS is produced. Through the simulation, the flow and separation of different-sized particles in VFFS are studied, and the reasonability of the simulation is verified by a pilot-scale screening experiment. The present study demonstrates the potential of the DEM method for the analysis of screening processes in VFFS.

Flow behaviors of ellipsoidal suspended particles in porous reservoir rocks using CFD-DEM combined with multi-element particle model

Flow behaviors of ellipsoidal suspended particles in porous reservoir rocks using CFD-DEM combined with multi-element particle model

Utilising grape juice processing by‐products as bulking and colouring agent in white chocolate

SummaryIn this study, grape pomace (mixture of grape seeds and skins) powder (GPP), obtained from grape processing, was used at different concentrations [10.0 (GPP10), 20.0 (GPP10) and 30.0 (GPP10) g/100 g] in white chocolate formulation for the partial replacement of sucrose. The results indicated that GPP addition at a higher concentration (>10.0 g/100 g) significantly affected the particle size, moisture content, texture and flow behaviour of white chocolate samples (P < 0.05). However, using GPP at a concentration of 10.0 g/100 g had advantages for physicochemical and flow properties. As expected, under simulated in vitro digestion conditions, the bioaccessibility of total phenolic compounds in saliva, gastric juice and intestinal juice for GPP10 samples was significantly higher than the control (P < 0.05). In conclusion, results of the study showed that it was possible to partially replace the sucrose with GPP at a concentration of 10.0 g/100 g in white chocolate formulations.

A dynamic coefficient of restitution applied to Two-fluid model in liquid-solid fluidized bed

In liquid-solid fluidized beds, the existence of the interstitial liquid among particles generates more energy dissipation different from that for gas-solid flows. To accurately predict the flow behavior of particles in a liquid-solid fluidization system, we simulate liquid-solid fluidization by introducing a dynamic coefficient of restitution model into the kinetic theory of granular flow. The dynamic coefficient of restitution is obtained by incorporating a semi-empirical correlation generated from a freely falling particle impacting a wet plate with a critical Stokes number, and the variable critical Stokes number is used to judge whether particles rebound after the collision. Simulated results show that the granular temperature and granular pressure are clearly affected when the dynamic coefficient of restitution model is introduced. As well, the particles velocity distribution predicted by the dynamic coefficient of restitution model is in better agreement with the experimental values compared with the constant coefficient of restitution.

Characterisation of solid hydrodynamics in a three-phase stirred tank reactor with positron emission particle tracking (PEPT)

It is challenging to measure the hydrodynamics of stirred tank reactors when they contain multiphase flows comprising liquid, gas bubbles and particles. Radioactive particle tracking techniques such as positron emission particle tracking (PEPT) are the only established techniques to determine internal flow behaviour due to the inherent opacity and density of fluid and the vessel walls. The profiles of solids flow are an important tool for robust reactor design and optimisation and offer insight into underlying transport processes and particle–fluid–bubble interactions for applications such as froth flotation. In this work, measurements with PEPT were performed with two tracer particles differing in surface hydrophobicity to characterise the solids hydrodynamics in a baffled vessel agitated with a Rushton turbine. The location data from PEPT were averaged with time to estimate the probability density function (PDF) of particle velocity in individual voxels. The peaks of these voxel distributions were used to produce profiles of solids flow in different azimuthal and horizontal slices. Bimodal vertical velocity distributions were observed in the impeller radial jet which suggest the particles experienced trajectory crossing effects due to inertia. Statistical tests were performed to compare the velocity distributions of the hydrophilic and hydrophobic tracer particles, which indicated similar average flow behaviour in the liquid or pulp phase of the vessel and differences near the air inlet, in the impeller discharge stream and pulp–froth interface. With tracers designed to represent gangue and valuable mineral species, the differences in velocity reveal interactions such as bubble–particle attachment and entrainment. • Positron emission particle tracking (PEPT) measurements of multiphase flow. • Solid hydrodynamics in a three-phase stirred tank reactor of gas, liquid and solids. • Comparison of hydrophilic and hydrophobic particle flow behaviour. • Observations of particle interaction with the gas bubble flow field.

Effects of the nozzle contraction angle on particle flow behaviors in a gas-particle two-phase jet

The particle dynamics of a conical jet with different contraction angles (the cone angle of the contraction wall, α = 20°, 40°, 60°, 80°) were investigated using particle image velocimetry (PIV) and optical fiber probes. The axial and radial distributions of particle-phase velocity and concentration were measured within a confined chamber at the mass loading ratio mp = 0.3–3.3 and jet Reynolds number Re = 11,843–104,497. Due to the nozzle contraction effect, the particle dynamics of conical jet are significant differences from the pipe jet and the smooth contraction jet. In the axial direction, there is a strong slip velocity between two phases near the nozzle exit (x/D = 0–6), which leads to the occurrence of particle acceleration. In the radial direction, the particles preferentially converge towards the centerline, forming the particle contraction, which intensifies the momentum transfer from the axial to radial direction and thus increases the particle dispersion. The particle acceleration and contraction are more pronounced with the increase of contraction angle. Furthermore, the order of the velocity decay rate and the spreading rate for different contraction angles are 40° > 80° > 60° > 20°. The nozzle contraction angle of 40° shows the best entrainment and mixing characteristics. In addition, the particles contraction near the nozzle exit as well as the particles accumulation in the wall region (r/R = 0.83–1.00) increase the non-uniformity of particle concentration.