Discrete Element Method Approach Research Articles

Numerical investigation of transport behaviors of nonspherical proppants in hydraulic fracturing using CFD-DEM

During hydraulic fracturing, conventional spherical proppant particles tend to settle rapidly in a low-viscosity fluid, which results in low permeability and poor supporting performance in the fractures. In this study, we introduce two types of novel nonspherical proppant particles; the transport processes of both the novel and conventional proppants in hydraulic fractures are simulated using the coupled computational fluid dynamics and discrete element method approach and multisphere modeling. We compare the differences in the transport performances of the nonspherical and spherical proppants. Sensitivity analysis of the fluid viscosity and particle density in the transport process revealed that both novel non-spherical proppants have better transport performance than the conventional spherical proppant. These results provide a strong basis for future proppant design and engineering practices.

Fluid-driven particle transport patterns in a confined geometry: Effect of flow velocity and particle concentration

Fluid-driven granular transport is involved in many important geomorphological processes and industrial applications such as unconventional hydrocarbon recovery. Yet it remains challenging to fully understand the granular transport mechanisms in confined geometries. By performing simulations based on a coupled computational fluid dynamics and discrete element method (CFD-DEM) approach, we systematically investigate the particle transport patterns and mechanisms driven by fluid flow between two parallel plates. Depending on the local drag force, the particles can settle or suspend in the fluid, leading to fluid-driven particle transport by creeping or by suspension. In the case of settle particle layers, fluid velocity variation in the vertical direction contributes to the relative motion between particle layers. Fluid-induced fingering patterns are observed in the upper layer of settled particles during the sliding. It is shown that the average finger length increases linearly with time and is affected by the flow rate and particle volume fraction. Increasing the flow rate shift the particle migration from creeping and sliding to suspension, which generally improves the particle transport efficiency. The obtained understanding of particle transport patterns in the confined geometries may have practical implications for industrial scenarios such as proppant transport in hydraulic fractures and sand production in extraction systems.

Particle–pore scale modelling of particle–fluid flows

A coupled approach of discrete element method and pore network model (DEM-PNM) is developed for simulating particle–fluid flow. By this approach, the particle/solid flow is described at a particle scale by DEM and the fluid flow is described at a pore scale by PNM. The coupling scheme between DEM and PNM and the boundary conditions for realizing particle–fluid flows under different conditions are explicitly introduced. The capability is examined in three systems: a dynamic cell, a gas-fluidized bed, and a packed bed with lateral gas injection. The simulated results by the DEM-PNM approach agree with those results by either DEM-LBM (lattice Boltzmann method) approach or experiments. In particular, the simulated reasonable flow patterns in gas fluidization and lateral gas injection demonstrate the applicability of the proposed approach to complex particle–fluid flow. However, the current model presents less accuracy in dilute flow region and does not consider some important factors, which should be further improved in the future.

Numerical investigation of heat conduction in heterogeneous media with a discrete element method approach

Composite materials have been widely used across industry sectors. However, they are characterized by a variability of thermal conductivity with the architecture and manufacturing processes. Hence, thermal transfer in composite materials requires an improved fundamental understanding. From numerical purposes, the Finite Element Method (FEM) seems a robust method to study heat transfer in composite material. However, it does not establish a high-fidelity with the real life of material since it is difficult to take into account potential damage matrix or interface imperfection by this method. As such, this paper discusses the development of numerical approach based on the Discrete Element Method (DEM) to study heat transfer in composite materials. For that purpose, we consider a hybrid lattice model based on the equivalence between a particulate domain and a continuous medium. Several works have used the DEM to study heat transfer in a homogeneous and continuous medium. Through this contribution, we aim to extend this approach to investigate composite materials. The model is then validated in terms of temperature by comparison with numerical and experimental results through several applications. Furthermore, a special care taken in the evaluation of the heat flux density fields. To the knowledge of the authors, previous works did not interest to the examination of heat flux density when using the DEM. Indeed, this sensitive to the packing configuration and consequently always heterogeneous even if there typically homogeneous. To overcome this problem, an original smoothing technique called Halo is proposed and discussed in this work. Results exhibit the relevance of the proposed approach to evaluate both temperature and heat flux density fields with a good degree of precision compared with th FEM, the Fast Fourier Transformer (FFT) based method and experimental data.

Stability and conductivity of proppant packs during flowback in unconventional reservoirs: A CFD–DEM simulation study

We present simulations using a coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) approach for a slurry of millimeter-sized particles in water which is squeezed between two walls and then made flow out though a narrow aperture. The process is akin to the flowback stage in the near wellbore zone of a hydraulic-stimulated well for hydrocarbon recovery. We consider different wall roughness and investigate its effect on particle production, final distance between walls, spatial particle distribution between the walls, and fluid production rate. We have found that the final distribution of particles changes significantly with small variations in the roughnesses of the walls. This in turn leads to production flow rates that may vary up to 50%. Although the main driver of the production for unconventional wells is the propped fracture network, these results suggest that the roughness of the fracture walls seems to play an important role in the final conductivity and therefore in the ultimate recovery.

Modeling Temporary Plugging Agent Transport in the Wellbore and Fracture with a Coupled Computational Fluid Dynamics–Discrete Element Method Approach

As the consumption of oil and gas resources is increasing, secondary exploitation in old wells and unconventional oil and gas exploitation methods are becoming increasingly important. As a result o...

Simulation of a Laboratory Scale Ball Mill via Discrete Element Method Modelling

Discrete Element Method (DEM) is a powerful tool for simulating different types of mills. It also used for computing different types of particles such as rocks, grains, and molecules. DEM has been widely used in the field of rock mechanics. In the present work, DEM approach is applied to model the milling media (powder particles and balls) inside a planetary ball mill and to estimate the distribution of particles of a dry powder during milling. In fact, the efficiency of the DEM strongly depends on the input parameters. The DEM simulation results indicated that DEM is a promising tool for the simulation of the dynamic particles motion and interactions within planetary ball mill. These results could be utilized to further develop the synthesis performance, anticipate the reaction, and reduce the wear in the dry milling reactions.

Computational Study of Heat Transfer Behavior in Fluid-Solid Fluidized Beds.

Heat transfer in fluid-solid fluidized beds is investigated using a combined of computational fluid dynamics (CFD) and discrete element method (DEM) approach, incorporated with a thermal model. The approach has taken into account almost all the mechanisms in heat transfer in fluidized beds. A comparison and validation of hydrodynamic and thermal data of fluidized bed obtained using CFD-DEM thermal approach with experimental and numerical results data in the literature is carried out. The simulations results reveal a good thermal steady state during the simulation time for calculating the thermal behaviors of fluidized beds like; the mean particle temperature, bed porosity, heat transfer coefficient and mean particle Reynolds number. The simulations results are showed a good agreement and consistency with the experimental and numerical data in the literatures. Thus, the integration of combined CFD-DEM with the thermal model is a step toward for the prediction, development the heat transfer efficiency in fluid-solid system, and the decrease of energy consumption of the industrial applications.

CFD-DEM study of particle-fluid flow and retention performance of sand screen

Sand screens are widely used to control sand production in unconsolidated reservoirs. Because of the lack of insightful understanding of this process, to date, reliably optimizing screen size is still a challenge. This paper presents a numerical study of the sand retention and production behaviors for widely used wire-wrapped screens by means of the combined approach of computational fluid dynamic (CFD) and discrete element method (DEM). The validity of the model has been verified by comparing the predicted critical slot sizes and sand production with published experimental results. On this basis, the effects of slot width-particle size ratios and wetting fluids, including gas and crude oil, are studied. The numerical results show that the increase in size ratio increases sand production, and the presence of fluid flow enhances sand production and causes unstable sand retention, which is more significant for crude oil compared to gas. Also, three mechanisms that allow the sand retention over a screen are identified, including stable bridging, bridging with intermittent collapse, and bridging with continuous collapse. Wetting fluids play an essential role in the sand production and bridging when the particle-fluid forces exerted on the particles near the slot are significant. Such forces induce strong localized particle-particle interactions in the nearby region over the slot, which accounts for the unstable bridging behavior.

A coupled CFD‐DEM investigation of suffusion of gap graded soil: Coupling effect of confining pressure and fines content

AbstractSuffusion involves fine particles migration within the matrix of coarse fraction under seepage flow, which usually occurs in the gap‐graded material of dams and levees. Key factors controlling the soil erodibility include confining pressure (p′) and fines content (Fc), of which the coupling effect on suffusion still remains contradictory, as concluded from different studies considering narrow scope of these factors. For this reason, a systematical numerical simulation that considers a relative wide range of p′ and Fc was performed with the coupled discrete element method and computational fluid dynamics approach. Two distinct macroresponses of soil suffusion to p′ were revealed, ie, for a given hydraulic gradient i = 2, an increase in p′ intensifies the suffusion of soil with fines overfilling the voids (eg, Fc = 35%), but have negligible effects on the suffusion of gap‐graded soil containing fines underfilling the voids (eg, Fc = 20%). The micromechanical analyses, including force chain buckling and strain energy release, reveal that when the fines overfilled the voids between coarse particles (eg, Fc = 35%) and participated heavily in load‐bearing, the erosion of fines under high i could cause the collapse of the original force transmission structure. The release of higher strain energy within samples under higher p′ accelerated particle movement and intensified suffusion. Conversely, in the case where the fines underfilled the voids between coarse particles (eg, Fc = 20%), the selective erosion of fines had little influence on the force network. High p′ in this case prevented suffusion.

Role of CFD based in silico modelling in establishing an in vitro-in vivo correlation of aerosol deposition in the respiratory tract.

Effective evaluation and prediction of aerosol transport deposition in the human respiratory tracts are critical to aerosol drug delivery and evaluation of inhalation products. Establishment of an in vitro-in vivo correlation (IVIVC) requires the understanding of flow and aerosol behaviour and underlying mechanisms at the microscopic scale. The achievement of the aim can be facilitated via computational fluid dynamics (CFD) based in silico modelling which treats the aerosol delivery as a two-phase flow. CFD modelling research, in particular coupling with discrete phase model (DPM) and discrete element method (DEM) approaches, has been rapidly developed in the past two decades. This paper reviews the recent development in this area. The paper covers the following aspects: geometric models of the respiratory tract, CFD turbulence models for gas phase and its coupling with DPM/DEM for aerosols, and CFD investigation of the effects of key factors associated with geometric variations, flow and powder characteristics. The review showed that in silico study based on CFD models can effectively evaluate and predict aerosol deposition pattern in human respiratory tracts. The review concludes with recommendations on future research to improve in silico prediction to achieve better IVIVC.

Discrete particle simulation of heterogeneous gas-solid flows in riser and downer reactors

The heterogeneous structures of the gas-solid flow in riser and downer reactors determine reactor performance but are not fully understood. This paper presents a numerical study of the hydrodynamic characteristics of cohesive particles in a riser and a downer. This is done by the combined approach of discrete element method (DEM) for particles and computational fluid dynamics (CFD) for the gas phase. The numerical results show that this CFD-DEM model can reproduce different annular dense distributions of particles in the fully developed sections of the riser and downer. This realization requires suitable periodic boundary conditions applied to both the gas and solid phases in the flow direction as well as adequately fine meshes. The flow behaviors are analyzed in detail in terms of particle flow pattern, cluster behaviors, gas and solid velocities and forces acting on particles. Also, the dependence of the dense solid ring in the downer on some pertinent variables related to pipe geometries, material properties, and operational conditions is examined.

Numerical investigation on horizontal wellbore hole cleaning with a four-lobed drill pipe using CFD-DEM method

The high efficiency of hole cleaning is essential and critical for drilling horizontal wells. In this study, the effects of four-lobed drill pipe on drill cuttings transport behaviors are examined using a coupled Computational Fluid Dynamics and Discrete Element Method approach. The drill cuttings concentration in annulus is used as the primary quantitative parameter, and the efficiency of hole cleaning is evaluated. Numerical results show that the curvature wall of four-lobed drill pipe by driving secondary motions and induces a local swirling flow, which promotes the transport of drill cuttings and significantly improves the hole cleaning performance. Compared with the conventional drill pipe, the hole cleaning efficiency of four-lobed drill pipe is improved by 89.7% on average, and the average kinetic energy of drill cuttings increases by one order of magnitude. These results are expected to provide a useful strategy for local hole cleaning when drilling horizontal wells.

Numerical Study on Particle Adhesion in Dry Powder Inhaler Device.

This study investigated the particle adhesion mechanism in a capsule of dry powder inhaler (DPI) based on a combined computational fluid dynamics and discrete element method (CFD-DEM) approach. In this study, the Johnson-Kendall-Roberts (JKR) theory was selected as the adhesion force model. The simulation results corroborated the experimental results-numerous particles remained on the outlet side of the capsule, while a few particles remained on the inlet side. In the computer simulation, the modeled particles were placed in a capsule. They were quickly dispersed to both sides of the capsule, by air fed from one side of the capsule, and delivered from the air inlet side to the outlet side of the capsule. It was confirmed that vortex flows were seen at the outlet side of the capsule, which, however, were not seen at the inlet side. Numerous collisions were observed at the outlet side, while very few collisions were observed at the inlet side. These results suggested that the vortex flows were crucial to reduce the amount of residual particles in the capsule. The original capsule was then modified to enhance the vortex flow in the area, where many particles were found remaining. The modified capsule reduced the number of residual particles compared to the original capsule. This investigation suggests that the CFD-DEM approach can be a great tool for understanding the particle adhesion mechanism and improving the delivery efficiency of DPIs.

Investigating the effect of flow direction on suffusion and its impacts on gap-graded granular soils

The flow direction is generally different from the gravity direction in geotechnical structures or slopes, the effect of which during suffusion remains unclear. This paper presents a coupled computational fluid dynamics and discrete element method approach to simulate the particle–fluid interaction relevant to this problem. The CFD-DEM approach is first benchmarked by a classic granular system problem, which is then used to investigate the characteristics of suffusion and its impact on the mechanical behavior. Five different angles between gravity and seepage directions for gap-graded soils with two fines contents are examined. Both the macroscopic and microscopic characteristics during suffusion and triaxial loading tests are analyzed. The direction angle is found to play a significant role affecting the erosion process and the mechanical consequence of soils. The results show that the greater the angle is, the harder it is for suffusion to occur and continue.

CFD-DEM simulation of pneumatic conveying in a horizontal pipe

In this paper, the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) is used to study pneumatic conveying in a horizontal pipe. A new three-dimensional modified wall roughness (WR) model and the discrete random walk (DRW) model are introduced into the CFD-DEM approach to simulate the effect of wall roughness and the random effect of turbulence on particle dispersion respectively. The interaction between particles and fluid of the pneumatic conveying in a horizontal pipe is calculated by both the one-way coupling method and the two-way coupling method. The flow characteristics of the pneumatic conveying in a horizontal pipe, including the particle velocity, the particle mass flux, and the particle trajectory are obtained by the simulations. The particle mass flux predicted by the CFD-DEM with WR-DRW is quite different with that predicted by the traditional CFD-DEM approach although the particle horizontal velocities obtained by two different approaches are similar, and the distribution of particles across the pipe cross section predicted by the CFD-DEM with WR-DRW is more uniform than that predicted by the traditional CFD-DEM approach. The accuracy of the CFD-DEM with WR-DRW is validated by the corresponding experiments from literatures. Comparing to the computational fluid dynamics - discrete phase model (CFD-DPM) without considering collision between particles, the CFD-DEM with WR-DRW developed in this work can be applied to study the pneumatic conveying in a horizontal pipe under both dilute and dense phase conditions.

Numerical investigation of mixed layer effect on permeability in a dynamic blast furnace

AbstractGas flow distribution in a blast furnace (BF) plays a significant role in BF smooth operation, productivity, and thermal efficiency. It is affected by the distribution of burden materials composed of alternating coke and ferrous ore layers. While moving downward coke and ferrous layers of different sizes can mix and form the so‐called mixed layers. Generally, the porosity is lower and hence the pressure drop is higher in the mixed layers. These variations can change the gas flow distribution and BF performance. Previous work tried to quantify the effect of material properties and process conditions on the formation of mixed layers and the resulting local porosity variation. However, these studies were often conducted under simplified conditions. Few were dedicated to the formation of mixed layers in a BF and its effect on BF performance. This work studies the formation of mixed layers in an experimental BF by using a combined computational fluid dynamics and discrete element method approach. The effect on BF performance was evaluated under different operational conditions including different size ratios of coke to iron ore particles, burden distribution, batch weight, and discharge rate. The results obtained were helpful to optimize burden charge for improving BF performance.

A fluid dynamic study of the active phase behavior in a rotary drum with flights of two and three segments

In the rotary dryers with flights, the drying occurs mainly in the active region where the material comes into direct contact with the air stream. The design of these flights is a complex task and studies are necessary to gain an in-depth understanding of the particle dynamics. This work aims to investigate the effects caused by angulations in flights of two and three segments on the particle dynamics, especially in the active region. The prediction of the solids flow was investigated by simulation using a Discrete Element Method (DEM) approach in an open-source software LIGGGHTS®. The simulated results were compared with experimental data using glass beads, with the rotary drum operating with 12 flights. The active region characteristics were analyzed using the responses variables: mass of solids in active phase, percentage of active region area occupied by the particles and the dispersion of the particles in the active region.

DEM Analysis of Track Ballast for Track Ballast–Wheel Interaction Simulation

This study aims to suggest a rational analysis method for a track ballast–wheel interaction that could be further developed to model the interaction in a train-derailment event, based on the discrete-element method (DEM). Track ballast is filled with gravel to form the trackbed. Although finite-element analysis (FEA) is widely applied in structural analysis, track ballast cannot be analyzed using conventional FEA because this approach does not allow separation of elements that share nodes. The DEM has been developed to analyze the dynamic behavior of separable objects, assuming that the objects are rigid. Therefore, track ballast can be modeled as separable rigid pieces of gravel, and its dynamic behavior can be analyzed using a rational contact model. In this study, a rational numerical strategy for track ballast–wheel interaction was investigated using the DEM approach. The suggested analysis method was validated through comparison with the experimental results of a drop test. In addition, case studies were conducted to investigate the effects of the contact-model parameters on the simulation result.

Size effect in heterogeneous materials analyzed through a lattice discrete element method approach

In the Lattice Discrete Element Method (LDEM), different types of mass are considered to be lumped at nodal points and linked by means of one-dimensional elements with arbitrary constitutive relations. In previous studies on the tensile fracture behavior of rock samples, it was verified that numerical predictions of fracture of non-homogeneous materials using LDEM models are feasible and yield results that are consistent with the experimental evidence available so far. In the present paper, a discussion of the results obtained with the LDEM is presented. A set of rock specimens of different sizes, subjected to monotonically increasing simple tensions, are simulated with LDEM. The results were analyzed from the perspective of the brittleness number, proposed by Alberto Carpinteri, to measure the brittleness level of the structure under study. The satisfactory correlation between the experimental results and LDEM results confirms the robustness of this method as a numerical tool to model fracture processes in quasi-brittle materials.