Flow Behavior Of Particles Research Articles

Numerical investigation on the pressure loss of coarse particles hydraulic lifting in the riser with the lateral vibration

This study focuses on the effect of the riser lateral vibration on the pressure loss of coarse particles hydraulic lifting by the numerical simulation. Euler-Euler two-fluid model based on kinetic theory is used to simulate the flow behavior of coarse particles in the riser, and the numerical model has been validated by using the experimental data. The dynamic grid technique is employed to simulate the lateral vibration of the riser. According to results of numerical simulation, the lateral vibration leads to the cyclical fluctuation of the pressure loss of coarse particles hydraulic lifting, and the average pressure loss of the dynamic riser is bigger than the static riser in general. The influence of the vibration amplitude, vibration period and modal shape on the pressure loss is analyzed, and the cause of pressure loss is also discussed.

Numerical simulation of the flow and erosion behavior of exhaust gas and particles in polysilicon reduction furnace

In order to study the flow and erosion behavior of gas-solid exhaust in the polysilicon reduction furnace, the flow characteristics of exhaust gas and silicon particles were analyzed. The flow model and erosion model of exhaust gas and silicon particles were established based on the gas-solid flow theory and the erosion theory. The erosion and wear behavior of the gas-solid mixture in the flow passage pipeline were studied by numerical simulation. The results show that the wear and erosion from Nos. 1 to 8 regions at the bottom of the ring were caused by silicon particles colliding with high angle. The wear and erosion of 2 regions from Nos. 9 to 10 at the outside of the up azimuth on both sides of loop pipe outlets, 4 regions from Nos. 11 to 14 on the upper and lower wall of single furnace main channel were severely affected wear regions, which is caused by silicon particles with low angle and high velocity. Through comparative analysis, the erosion of upper wall of single furnace main channel is most serious. Increased gas velocity, particle concentration and particle size will exacerbate the erosion and wear rate of the pipeline in polysilicon reduction furnace, but the distribution and development of severe wear zone would not be affected significantly.

Application of the kinetic theory of rough spheres to the simulation of the hydrodynamics of particles and liquid phases in a fluidized bed

The flow behaviors of liquid and particles in a fluidized bed are simulated using a liquid-solid two-fluid model, coupling with the kinetic theory of rough spheres. The expressions for the energy dissipation and viscosities of particles are adopted as functions of the tangential restitution coefficient and the restitution coefficient of particles, which consider the effects of particle rotation on the exchange and dissipation of particle energy. The simulated bed expansion height, particle concentration, particle velocity and total granular temperature differ from those not considering particle rotation. According to the simulation results, particle rotation enhances particle aggregation and decreases the bed expansion height, particle axial velocity and total granular temperature. The energy dissipation that is produced by particle rotation constitutes approximately 25% of the total energy dissipation in a liquid-solid system. In addition, two factors that affect particle rotation are explored by changing the tangential restitution coefficient of the particles and the liquid velocity. The simulation results demonstrate that the particle rotation effect is the most significant at β = −0.2, and the particle rotation is enhanced with the increase in the liquid velocity.

Effects of flow behavior index and consistency coefficient on hydrodynamics of power-law fluids and particles in fluidized beds

Flow behaviors of particles and power-law fluids were numerically simulated by means of Euler-Euler model with kinetic theory of granular flow in liquid-solid fluidized beds, and effects of flow behavior index (n) and consistency coefficient (K) were studied. The simulation results were compared with the experimental measurements, and good agreements were achieved. The effective viscosity of the shear-thinning fluid decreases as it flows through the expanded bed due to the increase in fluid strain rate. Unlike the homogeneous distributions of particles in Newtonian liquid fluidized beds, four regions for particle flow were observed along the bed height when a non-Newtonian fluid acts as the fluidizing agent, which indicates the non-uniformity of particles distribution. With the decrease of n, the enhancement of shear-thinning characteristics of the fluidizing agent thickens the relative inlet region and enhances the non-uniformity of particles along the bed height. The increase of n accelerates the circulation of particles in the fluidized bed, which speeds up the renewal of the particulate materials throughout the reactor space. The increase in K increases the apparent viscosity of the fluidizing agent. The bed height increases and the average solid volume fraction decreases. However, the influence of K on the non-uniformity of particles in the bed is less significant than that of n.

Determination of Dynamic Dispersion Coefficient for Solid Particles Flowing in a Fracture With Consideration of Gravity Effect

Abstract A robust and pragmatic method has been developed and validated to analytically determine dynamic dispersion coefficients for particles flowing in a parallel-plate fracture, in which gravity settling has been considered due to its significant impact on particle flowing behavior. More specifically, a two-dimensional (2D) advection–diffusion equation together with the initial and boundary conditions has been formulated to describe the flow behavior of finite-sized particles on the basis of coupling the Poiseuille flow with vertical settling. Meanwhile, three types of instantaneous source conditions (i.e., point source, uniform line source, and volumetric line source) have been considered. Explicit expressions, which can directly and time-efficiently calculate dynamic dispersion coefficient, have been derived through the moment analysis and the Green’s function method. By performing the simulation based on the random walk particle tracking (RWPT) algorithm, the newly developed model has been verified to determine particle dispersion coefficients agreeing well with those obtained from the RWPT simulations. It is found that the point source is the most sensitive to gravity effect among different source conditions, while the volumetric line source is affected more than the uniform line source. For particle size larger than its critical value, an increased particle size leads to a decreased asymptotical dispersion coefficient for all the source conditions due to the significant gravity effect, while gravity positively affects the dispersion coefficient at early times for the point source condition. In addition, average flow velocity positively affects the dispersion coefficient for all the source conditions, while the associated gravity effect is influenced only at early times for the point source condition.

An improved CFD simulation for investigation of the sand particles flow behavior in the sand shooting process

The flow behavior of sand particles has been examined by computational fluid dynamics (CFD) and experimental validations in sand shooting process. To avoid over-estimating the drag force between gas and solid phases, the energy minimization multiscale model(EMMS)has been incorporated. An applicable value of grid size is determined by grid dependency study. Three specularity coefficients are simulated to get an insight into the influence on the flow hydrodynamics of sand particles. The specularity coefficient affects tangential velocity and volume distribution of sand particles. No slip wall boundary condition is in better agreement with experimental data. With validation of sand shooting experiment, agreement is achieved between experiment images and simulation results. A comparison between EMMS drag model and Gidaspow model has been discussed in terms of simulating particles flow behavior with different particle diameters. The EMMS drag model has an accuracy prediction especially for smaller particles and dense flow.

Comparison of computational fluid dynamics–discrete element method and discrete element method simulations for a screw conveyor

AbstractFlow behavior of particles is simulated by means of discrete element method (DEM) in a screw conveyor. The gas flow is considered by the Euler model. The subgrid scale model turbulence model is applied to solve gas turbulence. A detailed description of the model equations applied has been presented. The comparison between computational fluid dynamics (CFD)‐DEM (i.e., considering gas flow) and DEM (i.e., not considering gas flow) simulation results is performed. Predicted mass flow rate with CFD‐DEM model is in better agreement with experiments by Roberts and Wills comparing with DEM results. The effects of incline angle and filling rate on the flow behavior of particles are predicted. The simulation results show that the gas flow has a major impact on particle flow behavior at a high rotation speed, whereas the velocity of particles increases with an increase of rotation speed. As the filling rate rises, both the translational granular temperature and the rotational granular particle temperature decline, which means that the particles fluctuation turns weak. While with an increase of incline angle, from the horizontal to vertical, the translational granular temperature is increased, but the rotational granular temperature reduces and then goes up. In brief, translational motion is a main mode of motion in a screw conveyor.

Investigation of the segregation of a binary particle mixture in a square circulating fluidized bed with air staging

To further understand the segregation characteristics of a binary particle mixture in a riser, the flow behaviors of particles with different sizes were experimentally and numerically investigated in a cold square circulating fluidized bed. The impact of the gas velocity, solid circulation rate, initial coarse particle fraction, and air staging on the coarse particle fraction and axial pressure drop were examined. The experimental results show that air staging can significantly promote the pressure drop of a binary mixture at the bottom of the bed compared with that of monosized particles. Meanwhile, the segregation of the binary mixture at the bottom is hindered. It was also found that there was clear radial segregation owing to a higher coarse particle fraction near the wall compared with the bed's center and its corner.

Application of GPU-DEM simulation on large-scale granular handling and processing in ironmaking related industries

Graphics processing unit (GPU)-based DEM combined with message passing interface (MPI) has been applied to large-scale handling and processing systems, including granular conveying, reclaiming, screening, ship loading, grab and screw unloading, and blast furnace top charging systems. The issues in terms of particle flow behaviour, particle-wall interaction/wall stress, particle energy dissipation, size segregation, and process efficiency, etc., are discussed. The results showed that for a belt conveying chute, wear became more severe at higher flow rates. In the reclaiming process, there was an increase in the digging resistance on the buckets with increasing bucket rotation speed. For the screening process, lower vibrating frequency lead to a higher screening efficiency, but also higher wall stresses. In a ship loading process, particle streams with a wide size distribution provided a significant cushioning effect on particle degradation, and when the dropping height reduces, the dissipated energy by particle-particle impacts greatly reduced. For a grab unloader, particle velocities became smaller with an increase in grab close time with tangential stresses only slightly reduced within the close time range considered. An increase of rotational speed of the bottom blades of a screw unloader indicated a higher unloading efficiency. A full blast furnace top charging process model was also developed. Size segregation was observed at different stages of the charging process. This paper demonstrated that GPU-based DEM can be successfully applied to the whole granular process chain of ironmaking related industries at different scales and provide guidelines for the key issues in different processes.

Experimental Study and DEM Numerical Simulation of Dry/Wet Particle Flow Behaviors in a Spouted Bed

In this study, wet particle flow behaviors were investigated in a spouted bed using numerical simulations and experiments. Effects of liquid contents and viscosities were investigated. For the expe...

Thermal Radiation Effects on Heat and Mass Transfer of Magnetohydrodynamics Dusty Jeffrey Fluid past an Exponentially Stretching Sheet

The heat and mass transfer of steady magnetohydrodynamics of dusty Jeffrey fluid past an exponentially stretching sheet in the presence of thermal radiation have been investigated. The main purpose of this study is to conduct a detailed analysis of flow behaviour of suspended dust particles in non-Newtonian fluid. The governing equations hav been converted into dimensionless form, and then solved numerically via the Keller-box method. The expression of Sherwood number, Nusselt number and skin friction have been evaluated, and then displayed in tabular forms. Velocity, temperature and concentration profiles are presented graphically. It is observed that large value of dust particles mass concentration parameter has reduced the flow velocity significantly. Increase in radiation parameter enhances the temperature, whereas the increment in Schmidt number parameter reduces the concentration.

Stress analysis of ore particle flow behaviour under the influence of a flexible barrier

Additional stresses caused by a flexible barrier, drawpoints and the self-weight of ore particles were investigated based on a physical experiment of the shrinkage stoping method of synchronous filling, and the flow behaviour of ore particles is described by the component forces. This study shows that when ore particles are drawn from multiple drawpoints under the influence of a flexible barrier, the stress distribution of the ore particles is sinusoidal, with an amplitude that gradually decreases with increasing height. The values of σx and σy gradually decrease with increasing height; the maximum σy values occur at x = 0, the maximum σx values occur at x = ± 10 and the maximum shear stresses occur near the lateral walls. The shape of the draw column is determined by the additional vertical stress, and its contour determines the essential morphology of the drawbody. The surface of the ore particles is smoothed by the additional stress caused by the barrier, and the self-weight of the ore particles is the inherent cause of the additional stress.

3D CPFD simulations of gas-solids flow in a CFB downer with cluster-based drag model

The interactions of gas and solids are important in determining the flow structures in the Circulating Fluidized Bed (CFB) downer. Proper description of the interphase drag model is thus crucial for simulating the downer. Considering that cluster with several numbers of particles can be present in the downer, an interphase drag model was developed by considering the dynamic equilibrium of the amount of particles in and out of the cluster in the downer, which was then incorporated into the Computational Particle Fluid Dynamics (CPFD) model. CPFD simulation results show that the predicted particle flow behaviors are in good agreements with experimental data under different operating conditions. Solids circulation rate and gas velocity can significantly affect particle flow behaviors especially in the acceleration region near the inlet. More amounts of particles flow faster in the center while a few part of particles flow slower near the wall, resulting that the particle residence time is shorter and uniform in the center and longer near the wall. The residence time distribution (RTD) curve of particles is narrower with a higher peak in the downer than in the riser. Simulation results indicate that less back-mixing of particles is present in the downer, and the flow structure in the downer approximates the ideal plug flow. The present method considering the cluster effect is reasonable in predicting the flow behavior and RTD of particles in the downer.

Deposition prediction in a pilot scale pulverized fuel-fired combustor

Fossil fuels have traditionally been used in power generation systems and represent the main source of greenhouse gas emissions from this sector. Renewable fuels, especially biomass, are now being substituted for fossil fuels to reduce CO2 emissions. Co-firing biomass with coal, which has been widely practised in the UK and Europe, is one route to reduce the environmental impact of using coal. However, the deposition of ash particles and vapour species on heat exchanger surfaces during operation is a serious issue in pulverised coal and biomass fired power plant as this reduces the plant thermal efficiency and can cause fireside corrosion, which limits component lives. Deposit formation is difficult to predict as it varies with many factors including: boiler geometry, combustion conditions and fuel composition.Computational Fluid Dynamics (i.e. CFD) is one of the best modelling tools to study the flow behaviour of gases and particles around heat exchanger tubes and predict deposition. This work used an Eulerian-Lagrangian model to describe the gas flow field around tubes and the solid ash particle trajectories respectively. User Defined Functions (i.e. UDFs) were developed for the CFD package to enable the prediction of deposit growth, deposit shape and temperature gradients around superheater/reheater tubes. Deposit build up insulates such tubes from the flow of the hot combusted gas stream and reduces heat transfer between this gas stream and the steam coolant following within the tubes, thus raising the deposit temperature. The CFD-based predictions generated were consistent with available literature data.The CFD deposition model has been applied to predict deposition on air cooled ceramic probes in a 100 kWth pilot-scale, pulverized fuel (PF) combustor and compared to deposition data measured after the combustor rig runs. For modelling purposes, the geometry was simplified to a two-dimensional domain with inert spherical ash particles dispersed in air and injected at an inlet plane. Experimental data from a series of rig runs have been used to test this CFD deposition modelling approach.

Numerical Simulation of Ore Particle Flow Behaviour through a Single Drawpoint under the Influence of a Flexible Barrier

A model of the mass draw and synchronous filling no-top-pillar shrinkage stoping method was created based on the particle element theory and PFC2D software. A numerical simulation of the ore particle flow behaviour through a single drawpoint under the influence of a flexible barrier was performed; following which, a visualization of the change process in the marked layers, draw column, flexible barrier, and cavity was obtained. Finally, the results demonstrated the following. (1) Before the ore particles at the highest horizon were drawn, the morphology of the draw column had an ellipsoidal (whole, closed, and approximate) shape, but after the ore particles were drawn, the morphology of the draw column had a gyroscopic shape (i.e., the shape of a spinning top). (2) The height of the draw column increased rapidly and exponentially in the early period of the draw, presented a linear growth tendency during the medium period with an increase in the accumulated mass drawn, and remained at a certain value in the later period. (3) The morphology of the flexible barrier presented a Gaussian distribution on the whole, but its bottom had an analogous parabola morphology, particularly in the late stage. (4) The cavity began to form with the ore particles at the highest horizon drawn; the cavity development presented an evolutionary process from the microscopic to macroscopic regime, and the morphology of the cavity was crescent in the early stage and triangular in the late stage.

Numerical study on pulverized coal combustion in a raceway from the viewpoint of coal plume

The combustion efficiency of pulverized coal particles in a blast furnace depends strongly on the particle flow behaviors and the shape of the main combustion zone, i.e., the raceway shape. With a coupling method, a raceway formation model and a multiphase reaction model were integrated to predict the raceway shape. The pulverized coal combustion under different operating conditions were simulated, and the combustion performance was analyzed regarding a low-burnout region inside the coal plume. The results show that the raceway shape affects the expansion degree of the plume and then the combustion performance. Increasing the oxygen enrichment rate in the blast significantly promotes the combustion reactions of particles in the inner region of the plume. With an optimal blast rate, the overall burnout rate can be improved with the centered particles having the highest oxygen accessibility.

Numerical simulation of gas-solid two-phase flow in a two-stage series riser using the filtered model

In order to study the hydrodynamics characteristics of gas-solid two-phase flow in the two-stage series riser, a filtered two-fluid model considering filter size, filtered solids volume fraction and slip velocity is used. Comparing to simulated results from different drag models including the filtered model, Gidaspow model and Wen-Yu model, the results from the filtered model are in better agreement with the experimental data of Zhu et al. Also, the details comparison of flow behaviors of particles between the two-stage series riser and typical riser are conducted. The enlarged section in the bottom for a two-stage series riser can strengthen the back-mixing of particles and gas-solid interaction. Simulation results reveal that the solids volume fraction displays the typical S-type distribution with an increase of solids mass rate, but the gap is declined along the bed height. The distributions of solids volume fraction, axial velocity and residence time are investigated by analyzing the simulated results at the different geometry of enlarged zone at the bottom of a two-stage series riser.

Simulation of Sand Filling Process and Analysis of Flow Behavior with Different Binder Ratio

Core shooting process has a great influence on the quality of sand cores. At present, there are two computational fluid dynamic models applied to simulate the hydrodynamics of core shooting process. In this paper, a two-fluid model (TFM) simulation is made on fluid dynamic analysis. With validation of experimental results and discrete particle model (DPM) simulations, the TFM is able to predict a reasonable flow behavior of sand particles by gas dynamic pressure analysis. Residual gas distribution of sand filling process is analyzed and a good agreement is achieved between air volume fraction simulation based on TFM and experimental results. A comparison between different binder ratios is made. The binder ratio has a significant effect on sand hydrodynamic behavior and the sand volume fraction.

Numerical investigation of turbulent flow behavior of sand particles in core shooting process

The core shooting process is the most widely used technology on sand core making and plays an important role on the quality of sand cores. However, the core shooting process has a complexity flow behavior of sand particles. In the current work, a computational fluid dynamics model- two-fluid model with incorporating the kinetic theory was adopted to investigate the hydrodynamic flow behavior of sand particles in sand shooting process. A comparison between laminar and turbulence model was made. The simulation results indicate that the turbulent flow has a significant effect on sand particles flow. The fluctuation of kinetic energy contributes to turbulent flow has a great effect on the sand volume distribution. A difference of sand volume fraction between wall and center of sand box occurs in turbulence model. The variation of solid velocity is nearly the same in both laminar and turbulence model.The variation of gas velocity has a more significant effect by different turbulence model than particle phase.

Numerical analysis of similarities of particle flow behavior in stirred chambers

Granular shear flows in chambers with rotating shafts are ubiquitous in manufacturing processes for numerous industries such as pharmaceuticals, food, and cereal processing, wherein flow homogeneity is critical to maintain product quality. In this work, Discrete Element Modeling (DEM) was used to study flow behaviors of rice particles using the special stirred chambers. The non-geometric similar chambers equipped with a regular polygon sieve and a roller shaft are used as simulated stirred chambers. This work's goal was to establish a similarity rule of the particle flow behaviors among these chambers. The gap between the shaft and the sieve periodically varies from maximum to minimum when the chamber is in work, which forms the gap curve. The kinematic flow behavior evaluated in this work were normalised velocity, normalised tangential velocity, radial velocity and radial distance distribution of particles. The dynamic flow behavior evaluated in this work was the particle collision energy. The DEM results were used to compare the kinematic and dynamic flow behaviors for the different chambers. The results indicated that both kinematic and dynamic flow behaviors were similar among chambers with the same gap curve. From these results and analysis, an empirical similarity rule of particle flow behavior, that is, the constant gap curve, was developed. Meanwhile, the effectiveness of the proposed similarity rule is experimentally confirmed. These findings are useful to understand and control the operational performance of the similar stirred chambers.