CFD-DEM Simulation Research Articles

Study on the char combustion in a fluidized bed by CFD-DEM simulations: Influences of fuel properties

In this paper, CFD-DEM method coupled with the thermochemical submodel is employed to simulate the char combustion in a three-dimensional (3D) bubbling fluidized bed. The influences of particle properties on the particle profile, temperature, and reaction rates are investigated in horizontal and vertical directions. The results showed char particles with four types of diameters have the similar characteristic distributions and variation tendency to those with different densities. The major difference is that the particle-averaged char combustion rate increases with the particle size, but slightly decreases with the increment of density. The mixing index of fuel particles and the internal relation between particle mixing, heat transfer, and reaction are also explored. It is revealed that the particle content profile is apparently affected by the movement of bubbles. The uniformity of distributions of particle temperature, CO and CO2 concentrations is consistent with fuel particle profile in most cases.

CFD-DEM Simulation of Fluidization of Polyhedral Particles in a Fluidized Bed

Fluidization of non-spherical particles is a common process in energy industries and chemical engineering. Understanding the fluidization of non-spherical particles is important to guide relevant processes. There already have been numerous studies which investigate the behaviors of different non-spherical particles during fluidization, but the investigations of the fluidization of polyhedral particles do not receive much attention. In this study, the investigation of the fluidization of polyhedral particles described by the polyhedron approach is conducted with a numerical CFD-DEM method. Experiments of the fluidization of three kinds of polyhedral particles are conducted under the same condition with corresponding simulations to validate the accuracy of our CFD-DEM model. The results indicate that our CFD-DEM model with the polyhedron approach can predict the behaviors of polyhedral particles with reasonable accuracy. Fluidization behaviors of different polyhedral particles are also investigated in this study. Compared to spherical particles, the motion of polyhedral particles is stronger, and mixing degree is higher under the same fluidization gas velocity.

A Study of RANS Turbulence Models in Fully Turbulent Jets: A Perspective for CFD-DEM Simulations

This paper presents an analysis of linear viscous stress Favre averaged turbulence models for computational fluid dynamics (CFD) of fully turbulent round jets with a long straight tube geometry in the near field. Although similar work has been performed in the past with very relevant solutions, considerations were not given for the issues and limitations involved with coupling between an Eulerian and Lagrangian phase, such as in fully two-way coupled CFD-DEM. These issues include limitations on solution domain, mesh cell size, wall modelling, and momentum coupling between the two phases in relation to the particles size. Therefore, within these considerations, solutions are provided to the Navier–Stokes equations with various turbulence models using a three-dimensional wedge long straight tube geometry for fully developed turbulence flow. Simulations are performed with a Reynolds number of 13,000 and 51,000 using two different tube diameters. It is found that a modified k-ε turbulence model achieved the most agreeable results for both the velocity and turbulent flow fields between these two flow regimes, while a modified k-ω SST/BSL also provided suitable results.

CFD-DEM simulations of riser geometry effect and cluster phenomena

In this paper the influence of the inlet and outlet configurations of a pseudo-2D fluidized riser on the hydrodynamics (i.e. flow pattern and cluster characteristics) are studied. A detailed comparison between experimental data and full 3D CFD-DEM simulation results is performed. Solids volume fraction and mass flux are characterized and particle clusters are detected in our CFD-DEM simulations and compared to experimental data. It is shown that a correct representation of the outlet is very important for a correct simulation of the solids holdup in the top section of the riser. The core-annulus flow behavior is generally well predicted by the model and cluster characteristics such as cluster occurance and velocity are also in good agreement with experimental data. Finally, an outlook is given for the future use of CFD-DEM simulation approaches to study riser flows.

Implementation, validation and application of a lubrication force model in CFD-DEM simulations

Implementation, validation and application of a lubrication force model in CFD-DEM simulations

Analysis of the Wettability Effect on Slag Holdup in a Fixed Bed of Carbonaceous Particles Using CFD–DEM Simulations

Analysis of the Wettability Effect on Slag Holdup in a Fixed Bed of Carbonaceous Particles Using CFD–DEM Simulations

Particle Distribution and Motion in Six-Stage Centrifugal Pump by Means of Slurry Experiment and CFD-DEM Simulation

Six-stage centrifugal pumps are used in deep-sea mining lifting systems and are required to convey slurry containing coarse particles. A six-stage centrifugal pump suitable for operation in a natural mining system was manufactured. High-flow and full-scaled slurry conveying experiments at a 5% and 9% volume concentration of particles was carried out at a large modified test site with artificial nodules. CFD-DEM simulations were carried out to obtain slurry transport characteristic curves, particle transport and distribution characteristics, where the simulation method was validated by the experiment data. A clarified two-stage pump can be used instead of a multi-stage pump for simplified simulation calculations with acceptable accuracy. Local agglomeration of particles caused by backflow was found at the outlet of the diffuser, and such agglomeration decreased with increasing flow rates. It was found that particles are transported non-uniformly, particles transport in diffusers in strands. Particles are transported in a pulse-like mode within the pump, with the latter stage showing similar particle characteristics to those transported in the previous pump stage.

DEM-CFD simulation of wood pellet degradation by particle-wall impact during pneumatic conveying

A numerical degradation model based on two key-functions, the so-called selection and breakage functions, is developed and implemented into a coupled DEM-CFD approach for investigating wood pellet degradation and fines formation during pneumatic conveying by particle-wall impact. The influence of operating conditions like air flow, product flow and solids loading ratio as well as of pipe component geometry on degradation is examined. Detailed insights into the flow field and particle motion are obtained. The inter-particle and particle-wall collisions are statistically analysed since they are the major cause of particle degradation.Apart from operating conditions, the bend radius is varied in four steps, supplemented by a 90°-Elbow as the worst-case scenario and a straight pipe section for reference. Increasing air flow rates, and thus higher particle velocities, as well as decreasing pellet mass flows and smaller bend radii result in progressive particle degradation. Particle-wall collisions turned out to be the major reason for particle breakage. Numerical results are compared to experimental data and show good agreement.

Resolved CFD–DEM simulation on hydrodynamic bridging in a bend rectangle channel

Resolved CFD–DEM simulation on hydrodynamic bridging in a bend rectangle channel

Numerical Simulation of Particle Dynamics in a Spiral Jet Mill via Coupled CFD-DEM.

Spiral jet mills are ubiquitous in the pharmaceutical industry. Breakage and classification in spiral jet mills occur due to complex interactions between the fluid and the solid phases. The study of these interactions requires the use of computational fluid dynamics (CFD) for the fluid phase coupled with discrete element models (DEM) for the particle phase. In this study, we investigate particle dynamics in a 50-mm spiral jet mill through coupled CFD-DEM simulations. The simulations showed that the fluid was significantly decelerated by the presence of the particles in the milling chamber. Furthermore, we study the particle dynamics and collision statistics at two different operating conditions and three different particle loadings. As expected, the particle velocity was affected by both the particle loading and operating pressure. The particles moved slower at low pressures and high loadings. We also found that particle–particle collisions outnumbered particle–wall collisions.

Computer simulation of the effect of particle stiffness coefficient on the particle-fluid flows

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective stiffness coefficient of particles for CFD-DEM simulations. The comparisons of the results indicate that although the application of stiffness coefficients with moderate values causes normal penetration depths of up to the particle radius, the simulations still show good results. The results also show that the stiffness coefficient and time step are strongly dependent of the fluid inlet velocities, particle diameters, particle inlet concentration and fluid type, and the simulation accuracy decreases greatly with increasing the time steps.

Simulation of proppant transport at intersection of hydraulic fracture and natural fracture of wellbores using CFD-DEM

Proppants transport is an advanced technique to improve the hydraulic fracture phenomenon, in order to promote the versatility of gas/oil reservoirs. A numerical simulation of proppants transport at both hydraulic fracture (HF) and natural fracture (NF) intersection is performed to provide a better understanding of key factors which cause, or contribute to proppants transport in HF–NF intersection. Computational fluid dynamics (CFD) in association with discrete element method (DEM) is used to model the complex interactions between proppant particles, host fluid medium and fractured walls. The effect of non-spherical geometry of particles is considered in this model, using the multi-sphere method. All interaction forces between fluid flow and particles are considered in the computational model. Moreover, the interactions of particle–particle and particle–wall are taken into account via Hertz–Mindlin model. The results of the CFD-DEM simulations are compared to the experimental data. It is found that the CFD-DEM simulation is capable of predicting proppant transport and deposition quality at intersections which are in agreement with experimental data. The results indicate that the HF–NF intersection type, fluid velocity and NF aperture affect the quality of blockage occurrence, presenting a new index, called the blockage coefficient which indicates the severity of the blockage.

On the drag force closures for multiphase flow modeling

Abstract Drag force models are one of the most important factors that can affect TFM and CFD-DEM simulation results of two-phase systems. This article investigates the accuracies, implementation issues and limitations of the majority of the drag models for spherical, non-spherical and systems with size distribution and evaluates their performance in various simulations. Around 1888 data points were collected from 19 different sources to evaluate the drag force closures on mono-dispersed spherical particles. The Reynolds number and fluid volume fraction ranges were between 0.01 and 10,000 and between 0.33 and 1, respectively. In addition, 776 data points were collected from seven different sources to evaluate the drag force closures on poly-dispersed spherical particles. The Reynolds numbers were between 0.01 and 500, fluid volume fractions between 0.33 and 0.9, and diameter ratios up to 10. A comprehensive discussion on the accuracy and application of these models is given in the article.

CFD-DEM simulation of the hydrodynamic filtration performance in balaenid whale filter feeding

Solid-liquid separation is a key link in environmental chemical and process engineering, including water purification, pollution treatment, etc. Traditional industrial filters are often clogged and damaged because they cannot be cleaned or replaced in time. Filter-feeders, on the other hand, are rarely clogged. Therefore, it is of great significance to draw bionic inspiration from biological filtration to guide the design of traditional filters. In this study, a computational fluid dynamics (CFD) and discrete element method (DEM) coupled model is adopted to investigate the filtering mechanism in balaenid whale feeding. In this model, DEM is used for the particle and the Navier-Stokes equation is used for the fluid. The effects of particle space and shape, as well as particle-particle/wall interaction, are considered. Then, the model is validated by comparing some crucial information with the theoretical results of previous literature. Finally, the effects of four key parameters on the filter feeding characteristics are analyzed, including the fringe layer permeability, prey incident direction, size and shape. The results show that the large permeability, random incidence direction, large size and real irregular shape all lead to more particle collisions. Besides, the captured prey is prone to form an uneven, backward aggregation trend. The large permeability and size make the trend of posterior aggregation more obvious. However, there are no significant differences in the number of the captured prey at each location for different types of incident directions or prey shapes. But the variation of the captured prey distribution in the real shape case is not as smooth as in the simplified sphere case, which shows that the increase in collisions changes the trajectories of some particles to some extent. This study provides a new idea for bionic design in solid-liquid separation field.

Coarse-grained CFD-DEM simulation to determine the multiscale characteristics of the air dense medium fluidized bed

Coal beneficiation via the air dense medium fluidized bed (ADMFB) has increased its popularity in recent decades. However, due to the coexistence of bubbles and the emulsion phases, obtaining a uniform and stable bed density for coal separation in ADMFB remains challenging. In this work, a coarse-grained CFD-DEM method with high accuracy in capturing the macroscale behaviors of the bed expansion rates and the axial solid concentration, was tested and validated. Besides, the microscale and mesoscale behaviors of the ADMFB were also analyzed via power spectrum density and wavelet decomposition. The findings show that the pressure fluctuation mainly results from bubbles motion of mesoscale rather than from particles motion of microscale and global bed expansion of macroscale. Furthermore, the apparent densities at different scales were calculated and a stable and uniform separation density was obtained within appropriate domains where the coal separation efficiency could be ensured.

Unresolved CFD-DEM simulation of spherical and ellipsoidal particles in conical and prismatic spouted beds

Various drag models were implemented in a superquadric CFD-DEM code and validated for the simulation of spherical and ellipsoidal particles in spouted beds. The most suitable drag models were identified by comparing the predicted local particle velocity with those measured by particle tracking velocimetry (PTV). The model by Beetstra et al. is the one that best reproduces the experimental results for the spouting of spherical particles, whereas the one by Sanjeevi et al. is the most suitable for ellipsoidal irregular ones. Their capability for the prediction of key operating parameters was demonstrated in both conical and prismatic spouted beds, as they correctly predict the minimum spouting velocity (ums) and fountain height in different configurations (without draft tube and different draft tubes) for particles of different size and shape. The CFD-DEM model predicts the preferential orientation of ellipsoidal particles at each location in the bed and the influence of internal devices on this parameter, which is of the utmost importance in the design of reliable coating apparatuses in the pharmaceutical industry.

Analysis of dust dispersion in the loading of a bulk carrier ship using CFD and DEM

Dust generation and dispersion continue to be a major concern for many in the industries that rely on bulk materials handling, and the ability to predict dust generation and dispersion remains challenging. This study looks at the use of computational fluid dynamics (CFD) and discrete element method (DEM) as a means of predicting dust generation and dispersion. The paper outlines work completed on predicting dust dispersion during the loading process of a bulk carrier using the Rotabox™ system for a stevedoring company at a port in Australia. CFD simulations are conducted to analyze the induced air flow generated inside the cargo hold of a bulk carrier including typical cross-wind conditions. Coupled CFD-DEM simulations are conducted to analysis the air flow inside the cargo hold driven by the unloading of the bulk material. Dust particle free-settling time is used to assess the dust cloud formation and dispersion based on the flow conditions predicted by CFD-DEM simulations. The study finds that the unloading process is likely to disperse dust into the cargo hold at a level that without dust suppression would result in dust being dispersed into the broader environment by the typical cross-wind conditions at the port.

Comparison of CFD-DEM and TFM simulations of single bubble injection in 3D gas-fluidized beds with MRI results

Predictions for bubble and particle dynamics surrounding a single bubble injected into an incipiently cylindrical fluidized bed from CFD-DEM and TFM simulations using different drag laws were compared with prior MRI results. This comparison allows for quantitative assessment of the accuracy of simulations for deterministic behavior of a single bubble as compared to statistical comparisons of chaotic free bubbling behavior as conducted in several prior studies. The comparison shows that simulations capture bubble rise velocity and particle velocity data surrounding bubbles fairly well. However, simulations tend to predict bubble shapes which are taller and narrower with larger wake angles than those observed experimentally. Changing drag laws does not have a significant effect on results, and significant quantitative differences are observed in moving from CFD-DEM to TFM simulations, yet neither provides predictions which are definitively better across a wide range of metrics. Some recommendations, including the use of novel drag laws and frictional solids stress models in TFM as well as the consideration of particle size distribution that may improve the prediction performance, are provided.

Direct comparison of CFD-DEM simulation and experimental measurement of Geldart A particles in a micro-fluidized bed

Although CFD-DEM simulation of Geldart B and D particles has been experimentally validated extensively, its experimental validation for simulating the hydrodynamics of Geldart A particles has been seldom reported, due to the fact that even the particle number in a laboratory fluidized bed is too much to be tracked individually. In this study, one-to-one comparison between experimental and CFD-DEM study of a miniaturized gas-solid fluidized bed (micro-fluidized bed) containing FCC particles was performed. It was shown that the bed expansion characteristics in bubbling fluidization regime, the mean voidage of emulsion phase as well as the bed collapse process can be predicted accurately by CFD-DEM method. The results not only provide experimental validation of CFD-DEM method for studying the heterogeneous dynamics of Geldart A particles in bubbling fluidized beds, but also prove that CFD-DEM method is an ideal and powerful tool for exploring the behavior of micro-fluidized beds.

Numerical Simulation on the Longitudinal Breach Process of Landslide Dams Using an Improved Coupled DEM-CFD Method

An accurate investigation of the landslide dam breach process is crucial for the understanding the breach mechanism and disaster prediction. However, the numerical research on the landslide dam breach process to date is rarely reported, especially regarding the soil-water flow coupling effect incorporated in the erosion process. This paper presents a numerical investigation on the longitudinal breach process of landslide dams via a coupled discrete element method (DEM) and computational fluid dynamics (CFD) with the volume of fluid (VOF). Moreover, a virtual sphere model is proposed to overcome the computational instability caused by the particle size approaching the mesh size. The accuracy and validity of the improved coupled method are verified using a series of single particle sedimentation cases. By employing this method, the longitudinal breach process of landslide dams featuring different materials and hydrodynamic conditions has been simulated. It is found to satisfactorily reproduce the longitudinal breach process of landslide dams including surface flow erosion, backward erosion, head-cut erosion, and water and sediment rebalance or complete breach. The effects of the inflow discharges and dam materials on the erosion process are systematically resolved. The breach flow can cause the rotation trend of particles and lead to the increase of tangential contact force at the initial stage of the dam breaching. During the breach process, both the strength and density of the force chain continue to attenuate. The results obtained from the improved coupled DEM-CFD simulations can reasonably explain the particle-fluid interaction mechanisms, physical and morphological evolution and breach process at both macroscopic and mesoscopic scales.