Computational Fluid Dynamics Discrete Element Method Research Articles

Determination of optimal air supply form on sludge convective drying process: A CFD-DEM study

Convective thermal drying is usually used in sludge dryers, and the air supply forms significantly affect the sludge drying efficiency. In this work, the drying process of multi-layered sludge is numerically simulated using a coupled computational fluid dynamics-discrete element method (CFD-DEM) approach. Better than our previous work, the current CFD-DEM model further considers the dynamic process of humidity within the flow field. Firstly, the CFD-DEM model is validated based on the mechanistic experimental data. Then, extensive numerical simulations are carried out to investigate the two-layered sludge drying process in the dryer, and the effects of two conventional air supply forms (Top-to-Bottom and Bottom-to-Top) as well as a novel air supply form (Side-assist) on the two-phase flow system are discussed. The simulation results provide in detail the dynamic processes of momentum, heat and mass (moisture) in the convective drying system under different working conditions. Following recommendations are presented to facilitate the operation of the dryer: Bottom-to-Top is better for sludge drying and tends to utilize less heat from the heat source compared to the Top-to-Bottom. The drying efficiency can be further improved by supplying the Side-assist with an optimal flow ratio of side-wind to bottom-wind. Numerical results show that the optimal flow ratio is related to the total air volume, the deflection angle and the side-wind temperature. The present study reveals in depth the impact mechanism of the air supply form on the convective thermal drying process of sludge, which contributes to the design and optimization of high-efficiency dryers.

Quantifying the effects of inlet gas and collision models in direct metal deposition using a CFD-DEM approach

Simulations of the powder jet in direct metal deposition (DMD) are often made with significant simplifications such as being incompressible, steady-state, or single-component, and do not provide explanation for the choice of parameters in the collision model. This work presents a coupled Computational Fluid Dynamics–Discrete Element Method model for the powder jet in DMD that considers all of the following features: compressibility effects, particle–wall and particle–particle collisions, turbulence, gas mixing, and melt pool boundaries. The goal of the simulation is to optimize the operating conditions and to predict the outcomes of experiments. After effective validation against experimental results, the effects of inlet gas, collision models and different boundary conditions in DMD have been comprehensively studied. It is demonstrated that gases with higher diffusivities, such as helium, are less effective shielding gases than those with lower diffusivities, such as argon. The increased wall temperature arising from the melt pool and track has little influence on the particle distribution.

A coupled computational fluid dynamics-discrete element method modeling for the dynamic behavior of the polar detector in a crushed ice environment during polar exploration

Investigating the dynamic behavior of polar detectors holds significance for the polar exploration of clean energy production. This paper uses computational fluid dynamics and the discrete element method, complemented by laboratory experiments, to systematically explore the water entry dynamics of a projectile passing through a zone of crushed ice accumulation. The research analyzes the influence of different crushed ice accumulation heights (ha) and water entry conditions on cavity formation, flow field distribution, and dynamic characteristics as the projectile passes through the crushed ice zone. Moreover, the influence of multi-body coupling on the movement of crushed ice and fluid is analyzed. The findings reveal alterations in the water entry behavior of the projectile due to the presence of the crushed ice accumulation zone. A notable two-way coupling mechanism between crushed ice and fluid is identified: crushed ice particles influence liquid level fluctuations and cavity evolution, while fluid flow impacts the movement of crushed ice particles. As the height of crushed ice accumulation increases, this coupling effect intensifies, leading to changes in the flow field distribution near the cavity and the hydrodynamic behavior of the projectile. While the alteration in water entry Froude number (Fr) may not significantly alter the evolution pattern of the liquid level flow field, it notably affects the distribution range and formation scale of the flow field characteristics. Additionally, the water entry Fr influences the load characteristics of the projectile as it passes through the crushed ice zone.

A coupled computational fluid dynamics-discrete element method modeling for the dynamic behavior of the polar detector in a crushed ice environment during polar exploration

Investigating the dynamic behavior of polar detectors holds significance for the polar exploration of clean energy production. This paper uses computational fluid dynamics and the discrete element method, complemented by laboratory experiments, to systematically explore the water entry dynamics of a projectile passing through a zone of crushed ice accumulation. The research analyzes the influence of different crushed ice accumulation heights (ha) and water entry conditions on cavity formation, flow field distribution, and dynamic characteristics as the projectile passes through the crushed ice zone. Moreover, the influence of multi-body coupling on the movement of crushed ice and fluid is analyzed. The findings reveal alterations in the water entry behavior of the projectile due to the presence of the crushed ice accumulation zone. A notable two-way coupling mechanism between crushed ice and fluid is identified: crushed ice particles influence liquid level fluctuations and cavity evolution, while fluid flow impacts the movement of crushed ice particles. As the height of crushed ice accumulation increases, this coupling effect intensifies, leading to changes in the flow field distribution near the cavity and the hydrodynamic behavior of the projectile. While the alteration in water entry Froude number (Fr) may not significantly alter the evolution pattern of the liquid level flow field, it notably affects the distribution range and formation scale of the flow field characteristics. Additionally, the water entry Fr influences the load characteristics of the projectile as it passes through the crushed ice zone.

A bilateral semi-resolved CFD-DEM approach for cost-effective modelling in a rotary drum

It is of significance to numerically describe particle-flow interphase flow details at a feasible computational cost. Inspired by the semi-resolved Computational Fluid Dynamics-Discrete Element Method (CFD-DEM), an improved bilateral semi-resolved CFD-DEM approach (BSM) approach is developed in this work. Compared with the conventional divided particle volume method (DPVM) and recent semi-resolved CFD-DEM (SM) approach, the BSM approach allows a higher-resolution mesh and achieves higher accuracy as well as applicability when simulating the transient flow with sharp gradients of solid volume fraction and velocity etc. Then the BSM approach is applied to a rotary drum to demonstrate the effectiveness by investigating the internal hydrodynamics details. The typical flow behaviours are detailed; then the effects of the restitution and friction on the internal flow are analysed with details to demonstrate its effectiveness in terms of repose angle, active–passive zone, solid residence time, particle mixing and axial dispersion. The results show a positive correlation of the active depth, mixing degree, and particle dispersion with the friction, while restitution increasing depicts no significant effects on this particulate flow. This work provides an improved numerical tool for understanding the multiphase transient flows involving sharp gradients.

CFD-DEM study of thermal behaviours of chip-like particles flow in a fluidized bed

Chip-like particles are increasingly practised in various thermal applications, yet the unique heat transfer characteristics are not well understood. In this work, a recently developed super-quadric computational fluid dynamics-discrete element method (CFD-DEM) is extended to couple with heat transfer sub-models to study the cooling behaviours of chip-like particles in a three-dimensional (3D) cylindrical fluidized bed. Then the effect of aspect ratio (AR) on the flow and thermal behaviours of chip-like particles are studied at the particle scale. The results show that the chip-like particles with an AR of 6 show the steepest temperature decrease and thus the fastest cooling process under the given conditions. The unimodal distributions of particle temperature for the small ARs (i.e., 2 and 4) but bimodal distributions for the large AR (i.e., 6) are captured. Further, a large convective heat flux appears in the dilute phase due to vigorous slip velocity and temperature difference while a small convective heat flux occurs in the dense phase where the chip-like particles tend to be in a close-packing status. Finally, the underlying mechanism is explored: the chip-like particles with larger ARs show better heat transfer performance because the AR enhances gas-solid relative movement intensity and the convective heat transfer flux, and the convective heat transfer dominates the whole particle cooling process. The fundamental study sheds light on the design and optimization of fluidized beds of chip-like particles including solar panel recycling and wood chip gasification.

Effect of the Volume Concentration of Binary Mixed Particles on the Flow and Wear Characteristics of Centrifugal Pumps

Solid–liquid two-phase centrifugal pumps are important fluid transport components in production and life. Most of the studies about the influence of solid-phase parameters on fluid transport mostly focus on single-component solid particles. In this work, two kinds of glass beads with particle sizes of 2 mm and 0.4 mm were used to study the effect of the binary mixed particle volume concentration on the internal flow and wear characteristics of a centrifugal pump. The flow distribution of the binary mixed particles in a centrifugal pump and the interactions between the particles and flow components at different volume concentrations (Cv = 5%, Cv = 7.5%, Cv = 10%, Cv = 12.5%, Cv = 15%) were studied using a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM). The research results show that with the increase in particle volume concentration, the head and efficiency of the pump decrease. Additionally, the distributions of the particles with different concentrations in the impeller flow passage were obtained. Moreover, the coupling force of the flow field acting on the particles decreases with the increase in particle concentration and the time it takes to convey small particles decreases with the increase in concentration, while that of large particles decreases first and then increases. Furthermore, the contact force between the particles and the blade changes periodically with time, and the wear of the centrifugal pump is mainly concentrated on the pressure surface of the blade and the wall of the volute outlet side; the wear rate increases as the particle concentration increases.

Micromechanical analysis of contact erosion under cyclic loads using the coupled CFD‒DEM method

Different layers of soil often have distinct particle sizes. When exposed to the natural environment, soil is easily affected by natural rainfall, rising groundwater levels, and human activities, leading to particle contact erosion, which reduces the safety and service performance of the soil structure. In this paper, a coupled computational fluid dynamics–discrete element method (CFD–DEM) model was employed to investigate the particle migration phenomena, mechanical response of contact interfaces, variations in flow fields, and macroscopic deformation during the contact erosion process under cyclic loads at different frequencies and amplitudes. The conclusions are presented as follows: (1) Within one cycle of cyclic loading, both compression during loading and stress relaxation during unloading are the main factors triggering the migration of fine particles. (2) The migration and loss of fine particles mainly occur in the early stages of cyclic loading, where strong contact force chains are formed within the fine particle layer, leading to significant plastic deformation of the soil at the macroscopic level. (3) Under cyclic loading, changes in the soil pore structure cause an upwards hydraulic gradient in the initial quiescent water flow field. This hydraulic gradient can rupture weak contact force chains and cause particle pumping. (4) Increasing the frequency and amplitude of cyclic loading intensifies the erosion of fine particles, causing greater axial deformation of the soil. Compared to cyclic loading frequency, the amplitude of cyclic loading has a greater impact on contact erosion.

Influence of particle stacking modes on the fluidization characteristics of biomass particles in binary particle systems

Spouted bed is widely used in biomass combustion and other industrial production due to the advantages of good heat transfer performance and sufficient gas–solid mixing. In order to achieve higher heat and mass transfer performance and conversion efficiency, inert particles are often added to assist in the fluidization of biomass particles. However, the stacking patterns of different particles in a binary particle system can have some effects on particle flow, distribution, and bed stability. Therefore, in this study, the computational fluid dynamics–discrete element method was used to analyze the particle fluidization characteristics under four different particle stacking modes in a spouted bed. The results show that the average bed height of larger spherocylindrical particles is prioritized in binary particle systems. The void fraction of spherocylindrical particles tends to increase in the near-wall region, whereas spherical particles tend to decrease. When the binary particles are mixed at the initial moment, the change rule of vertical velocity of the two particles remains consistent. In addition, the vertical velocities of two kinds of particles when layered stacking is used are gradually close to each other only after a period of time. In addition, the orientation angle of the spherocylindrical particles in the spouted bed tends to be horizontal for both the single-component spherocylindrical particle system and the wall effect attenuates this phenomenon.

Hydromechanical analysis of slurry infiltration with coupled CFD–DEM method

AbstractThe tunnel face stability is closely related to the migration behavior and clogging mechanism of the slurry particles in granular soils, which is not yet fully understood. In this study, the coupled computational fluid dynamics–discrete element method (CFD–DEM) is adopted to investigate the infiltration behavior of slurry at the particle scale. The full Johnson–Kendall–Roberts (JKR) contact model describing interparticle behavior that accounts for cohesion present even when particles are microseparated after collisions is adopted for clay‐clay or clay‐sand particles and the Hertz–Mindlin model is used for sand‐sand particles. Through simulations, the mechanism of the slurry particle's blockage is identified as physical, frictional and cohesive modes, and slurry particle migration usually undergoes the process of aggregation‐destruction‐migration‐reassembly. Meanwhile, the influences of pressure, cohesive force, and particle shape on infiltration are also analyzed. The results indicate that high pressure lengthens the infiltration path and increases the infiltration rate. The increase in cohesion enhances the effective clogging of the sand column by the slurry, and particles with smaller sphericity are more likely to clog in the sand column. These findings may enhance our understanding of the slurry infiltration mechanism and its practical application in TBM tunneling.

Silver Recovery from Crystalline Silicon Photovoltaic Solar Cells using Continuous Stirred-Tank Reactors.

Silver can be recycled from the end-of-life (EoL) crystalline silicon (c-Si) photovoltaic (PV), yet the recycling and its technology scale-up are still at an early stage especially in continuously stirred tank reactors (CSTR). In this work, the silver recovery from the solar cells is technically understood and optimised in the CSTR system from the point of view of silver recovery efficiency, through integrating experimental and numerical investigations. Specifically, based on the experiments, a kinetics model is developed and SEM surface morphology is characterised; and a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) particle-scale model is integrated with the kinetics model and validated against the fluid-flow pattern and silver leaching performance results from lab measurements. The validated CFD-DEM model is then applied to understand the particle-scale behaviour of silver leaching in the CSTR system in terms of hydrodynamics and AgNO3 distribution under different impeller speeds. The simulation results show that the silver leaching performance is improved in an improved CSTR design with a lower impeller position and doubled impeller layers. This work reveals the effectiveness and underlying hydrodynamics of silver leaching in CSTR systems and lays a foundation for improving silver recovery in PV recycling. This article is protected by copyright. All rights reserved.

Prediction of the sulfur driven autotrophic denitrification process via CFD-DEM approach

Sulfur driven autotrophic denitrification is an economic and efficient means to purify the nitrogenous wastewater. The long-term experimental study is quite time-consuming and expensive. In this work, a coupled computational fluid dynamics-discrete element method (CFD-DEM) is implemented to investigate the performance of long-term operating sulfur autotrophic denitrification process. The evolution of particle accumulation and nitrate removal efficiency in the packed bed reactors with different tube diameters and sulfur particle sizes are simulated. It is found that the NO-3-N removal rates for different tube diameters are close and a wider particle size distribution is shown in the slender reactor. The small particle bed shows a better NO-3-N removal efficiency.

Wurster fluidised-bed coating: Coarse-graining technique within CFD-DEM in conjunction with heat and mass transfer

In this study, we use a combined CFD-Discrete Element Method to assess predictive capabilities and numerical implications of a coarse-graining technique in Wurster fluidised-bed coaters. We investigated both hydrodynamics and heat and mass transfer and conducted simulations of a full three-phase system for the original and three coarse-grained systems, analysing velocity distributions, macroscopic solid stresses, moisture content and phase temperatures. We achieved a logarithmic simulation speed-up by aggregating up to 64 original particles into each coarse grain. This was accomplished while maintaining fidelity to the original CFD-DEM system in terms of reproducing with high accuracy macroscopic granular flow properties in different regions of a coater (drying, tube and bed regions). By integrating a liquid spray and humid air, we demonstrated that the phase temperatures were accurately predicted within the coarse-grained system, with a high capability of delivering liquid spray distributions with the same uniformity and drying. We also give arguments for choosing a certain degree of coarse-graining as a compromise between a desired reduction of computational costs and a trustworthy reproduction of granular-flow physics encountered in different regions of a Wurster bed. Our findings pave the way to using CFD-DEM to industrially-scaled Wurster-bed systems, which is currently unfeasible due to prohibitive computational costs.

Simulating aerosol droplet dynamics and coalescence in tracheal intubation insights from a CFD-DEM analysis of PSAR tube interactions

This study employed the Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) to investigate targeted droplet delivery in tracheal intubation. Our findings reveal that droplet behavior and deposition patterns are significantly influenced by droplet size. Smaller droplets (3 μm and 5 μm) closely follow airflow, showing similar deposition patterns in both CFD-DEM and CFD-DPM simulations. In contrast, larger droplets (7.5 μm and 10 μm) demonstrate increased deposition, particularly in the bent section of the Point Source Release tube (PSAR tube), due to enhanced inertia following collisions and coalescence. The study highlights that larger droplets experience a higher frequency of coalescence, especially in curved tube sections. This leads to altered droplet size distribution at the outlet, affecting deposition in the lower respiratory tract. These insights are crucial for optimizing inhalation therapy devices, emphasizing the importance of considering droplet interactions in CFD simulations to accurately predict aerosol behavior in pulmonary drug delivery systems.

Effects of operating parameters and particle friction on water usage of deep-sea manganese nodules hydraulic conveying equipment

One of the primary concerns for commercialising deep-sea mining is the environmental impact associated with the pumping seawater. Therefore, this study developed an unresolved coupled model of Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) to explore water usage under various operating conditions. The model was validated by experimental results from previous research. The study specifically focused on examining the effects of particle friction on the particle output rate and water usage. The results indicated that to minimise the usage of seawater, the injecting speed should be set at a relatively high value to achieve a high discharge rate, such as 3 m/s in this work. The injecting speed for large particles can be set lower than that for small particles. It is recommended to set the pumping flow rate at a relatively low value, as long as it can generate enough lift force to transport the particles.

Sustainable dye extraction: Annatto powder production in a fountain confined spouted bed

AbstractThis study proposes an efficient and sustainable process for annatto powder production using a fountain confined spouted bed. With widespread applications in industries such as food, pharmaceuticals, and cosmetics, conventional extraction methods face environmental and economic challenges. Our study explores a solvent‐free and eco‐friendly approach using mechanical attrition within a fountain confined spouted bed, offering a cost‐effective solution for annatto cultivation. We systematically investigated the impact of four parameters—fountain confiner position and length, draft tube diameter, and airflow velocity—employing experimental design, multiple regression analysis, particle swarm optimization, and computational fluid dynamics–discrete element method (CFD‐DEM) simulations. The proposed optimization condition shows significantly higher collision intensity, improving annatto powder production compared to other central composite design tests. This study contributes to developing of a sustainable and economically viable method for dye production, with potential implications for annatto‐producing regions globally.

Effects of natural fracture reopening on proppant transport in supercritical CO2 fracturing: A CFD-DEM study

The reopening of natural fractures reshapes the proppant beds in hydraulic fractures, especially at fracture intersections, critically influencing subsequent proppant migration. However, studies on the effects of proppant bed shapes on post-reopening proppant migration are limited. To address this gap, a moving wall boundary technique is integrated into a Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) framework to model natural fracture reopening, enabling an in-depth analysis of how proppant bed reshaping impacts subsequent proppant migration during supercritical CO2 fracturing. Results reveal that proppant migration into natural fractures is governed by both drag force-induced and gravity-induced rolling mechanisms, with the latter exerting a more significant effect. The gravity-induced rolling mechanism is enhanced by five key factors: (a) the generation of a well-developed proppant pack in proximity to the intersection; (b) the inadequately filled V-shaped gully; (c) the increased proppant transport capacity within the natural fracture; (d) the reduced bypassing of proppants at the intersection; and (e) the improved ability of proppants to enter the natural fracture. The enhanced gravity-induced rolling mechanism significantly increases the proppants flowing into natural fractures: by 35.6% between the central and rearward section cases, 168.9% from mild to severe plugging cases, 39.1% with a wider natural fracture width (1.5 mm–2.5 mm), 20.3% with decreased hydraulic fracture flow rate (0.35 m/s to 0.25 m/s), and 33% with reduced fluid temperature (160 °C–40 °C). These findings underscore the impact of natural fracture reopening on subsequent proppant migration, offering valuable insights for optimizing fracturing designs.

Particle dynamic behaviors in bubble curtain barriers blocking the diffusion of sediment

Bubble curtains are linear multiphase plumes that are used in industry and engineering to reduce diffusive flows between two zones. The circulating shear flow generated by the bubble plume can effectively create a particle barrier in the water; thus, it is also widely used to suppress the diffusion of suspended particles during dredging operations. To clarify the interaction mechanism between the bubble curtain and suspended particles under pressure-driven flow, experimental studies and numerical simulations were conducted to investigate the particle dynamics in the flow field around the bubble curtain. In this study, we established a formal analogy between a bubble curtain and an air curtain and qualitatively identified four typical distribution zones of the particles in the flow field. Based on the quantitative measurements and theoretical considerations, the optimal operating conditions and the upper limit of effectiveness of the bubble curtain were determined. In addition, the blocking behavior and efficiency of bubble plumes on particles with different ReU and FrUgnumbers and different particle properties were simulated via the computational fluid dynamicsdiscrete element method (CFDDEM) numerical simulation method.

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Impact of several coarse-graining models on a pilot-scale fluidized bed behavior using discrete element method–computational fluid dynamics

Fully coupled discrete element method for graded particles transport in pipes

Hydraulic conveying of graded particles is much more complex than that of uniform particles but is not fully understood. A fully coupled computational fluid dynamics–discrete element method model is established for the hydraulic conveying of graded particles, which integrally considers the particle–fluid and particle–particle interactions and turbulence modulation from particles. The proposed model accounts for the stochastic motion of particles by the discrete random walk method and applies the diffusion averaging algorithm to obtain particle concentration in arbitrary cells for smooth and cell-independent data fields on unfavorable cells (fluid cell size ≤ particle size). The particle–fluid drag force is applied to slurry flows through densely packed particle beds due to the consideration of porosity modification. The proposed model well performs in simulating the hydraulic conveying of dense graded particles. Dynamics in slurry mixtures of bi-disperse particles are investigated regarding different particle size compositions. The results show obvious stratification between coarse and fine particles, e.g., fine particles settling at the pipe bottom elevate the coarse particles and form a “lubrication layer” with high velocity. The torque caused by particle–particle/wall contact is greater than the torque caused by the fluid. The pipe cross section is divided into four regions according to the particle angular velocity. The effect of particle concentration on liquid motion is small because the difference in local particle concentration is relatively small, but the maximum pressure drop corresponds to a critical particle size composition.