CFD-DEM Simulation Research Articles

A CFD-DEM Simulation of Droplets in an Airless Spray Coating Process of a Square Duct

The purpose of this paper is to provide a numerical simulation, taking into account the collisional interactions of droplets in an airless rotary spray coating process. The hydrodynamics of gas and droplets are simulated using the CFD-discrete element method (DEM) with the JKR contact model in an airless rotary spray coating process of a horizontal square duct. The surface energy parameter used in the JKR model is calibrated using a virtual accumulation angle test in the funnel device. Based on the distribution of accumulation angles, a suitable surface energy for wall droplets is proposed. A rational gas RNG k-ε model is suggested in accordance with the comparisons of velocities, standard deviations, and the skewness of droplet number fractions from three turbulence models. The simulations of droplet film thicknesses agree with measurements from the literature regarding the film thickness along a vertical panel. The correlations of the exit gas and droplet velocities of sprayer holes are proposed with a discharge coefficient of 0.85 for gas and 5.87 for droplets. A number index of droplets is introduced in order to measure the uniformity of droplet distributions. A low droplet number index is found at low rotational speeds, representing a more uniform distribution of droplets as the rotation speeds reduce within the square duct. The normal force between the droplet and the wall is approximately an order of magnitude larger than the droplet–wall tangential force of collisions.

Introducing an efficient capped fluidized bed and quantifying its flow and heat transfer performance

Fluid-solid particle beds have a very wide range of industrial applications but there are few publications relating to a general method to quantify solid particle bed performance for a comparative efficiency study. The conventional approach of characterizing bed efficiency involves bubble sizes, bubble frequency, byproduct quantity for bed reactors, and pressure drop for minimum fluidization. However, different solid particle beds have different states with varying flow rates, which makes the comparative study more difficult to achieve. In this work, a common approach to measure solid particle bed efficiency in terms of heat transfer is presented. The two cases considered here are 1) When work is done by the particles such as in a catalytic reactor, and 2) When work is done on the particles such as in cooling/drying of particles. In addition to the packed bed and fluidized bed, a solid particle bed called a capped fluidized bed is introduced. The Eulerian–Lagrangian method, also known as CFD-DEM simulation, is adopted for this analysis. Numerical simulations show potentially significant advantages of capped beds over packed and fluidized beds under certain fluidization states. Capped fluidized bed pressure drop is comparatively lower than that for a packed bed and similar to a fluidized bed, which allows it to operate at a wider range of flow states. Current fluidized bed performance is limited by the entrainment and possible loss of particles at high flow rates. However, the capped fluidized bed restricts the particles from leaving the bed and thus permits higher flow rate operation. Further experimental research is required to more completely characterize this type of solid particle bed.

Resolved CFD-DEM simulation of proppant aggregating and bridging mechanisms in a narrowing fracture

In this work, we establish a resolved coupling model that integrates computational fluid dynamics and discrete element method (i.e., resolved CFD-DEM) to numerically reproduce the proppant bridging phenomenon reported in previous experiments and further reveal the underlying mechanisms leading to proppant bridging. Out study reveals that the CFD-DEM model with the consideration of an appropriate cohesion energy density parameter (e.g., 5 × 104 N/m2 in our models) can reasonably well capture the micro-scale dynamic features of proppant aggregating and bridging occurring at the fracture tip. Moreover, our simulations indicate that the critical ratio of the fracture width to the mean particle diameter leading to proppant bridging is approximately 1.9, which agrees well with experimental results. In a closed boundary fracture model considering fluid leak-off, proppant size significantly influences aggregating locations: smaller proppants are trapped close to the fracture tip, while larger proppants are aggregated at locations close to the fracture inlet.

Effect of immersed tubes configurations on mixing and heat transfer of mixed biomass and silica sand in a bubbling fluidized bed using CFD-DEM and statistical experimental design analysis

The presence of immersed tubes within fluidized beds enhances mixing efficiency and heat transfer. However, the influence of design parameters remains unexplored systematically. This study investigates the impact of design parameters on mixed biomass fluidized beds with immersed tubes employing a combined approach of CFD-DEM simulations and 2k factorial design analysis. Findings reveal that the angle between tubes and tube diameter are primary influential parameters, significantly influences particle mixing and heat transfer efficiency. Optimal conditions, identified through analyses of averaged mixing index and heat transfer coefficient, point to a staggered configuration with specific dimensionless of tube diameter per column width of 0.0515 and a tube spacing per tube zone height of 0.14. These insights offer valuable guidance for optimizing and emphasize the significance of design parameters incorporating immersed tubes, providing practical guidelines for enhancing mixing efficiency and heat transfer in various applications, especially those employing mixed biomass and silica sand.

CFD–DEM Simulation of Heat Transfer and Reaction Characteristics of Pyrolysis Process of MSW Heated by High-Temperature Flue Gas

Pyrolysis is a promising disposal method for municipal solid waste (MSW) due to the high-value utilization of the organic components of MSW. Traditional indirect heating has low heat transfer efficiency and requires an increase in the heat exchange area. In this study, a refined numerical simulation model for the pyrolysis of four typical MSW components with high-temperature flue gas was established to study the influence of flue gas on the heat transfer and reaction characteristics of MSW. The temperature distribution and particle size change in different components were obtained, and the effects of flue gas temperature and velocity on the pyrolysis process were analyzed. It was found that the temperature difference of the four components along the bed height direction was about 1.36–1.81 K/mm, and the energy efficiency was about 55–61%. When the four components were uniformly mixed, the temperature increase rates of each component were similar during the pyrolysis process. As the flue gas temperature increased, the amount of gas consumption decreased and the energy efficiency increased. When the flue gas velocity increased, the flue gas consumption increased and the energy efficiency decreased. The research results are of great significance for the promotion and application of pyrolysis technology to MSW with high-temperature flue gas.

Stabilization of closed-cell aluminum foam by particles in the presence of oxide film: CFD-DEM simulation on particle behavior for node-Plateau borders system

In order to reduce the particle addition in closed-cell aluminum foam, the effect of particles on foam drainage behavior was investigated numerically. The coupled CFD-DEM method was used to analyze the particle behavior within the node-PBs system. The predicted results agree well with experimental results. The results show that the trajectory of particles in metallic foam is consistent with literatures. Particles grow into clusters and deposit on the oxide film, leading to foam clogging and suppressing the drainage in aluminum foam. The above mechanism explains the phenomenon in literatures that the viscosity obtained from the drainage experiment is much greater than the apparent viscosity of the particle-melt mixture. The effect of particles on suppressing drainage is summarized as the blockage effect of stationary particles and the increasing apparent viscosity of moving particles. There is an optimization possibility of particle size and volume fraction, achieving better performance and lower production costs.

Coupled CFD-DEM simulation of interfacial fluid–particle interaction during binder jet 3D printing

The coupled dynamics of interfacial fluid phases and unconstrained solid particles during the binder jet 3D printing process govern the final quality and performance of the resulting components. The present work proposes a computational fluid dynamics (CFD) and discrete element method (DEM) framework capable of simulating the complex interfacial fluid–particle interaction that occurs when binder microdroplets are deposited into a powder bed. The CFD solver uses a volume-of-fluid (VOF) method for capturing liquid–gas multifluid flows and relies on block-structured adaptive mesh refinement (AMR) to localize grid refinement around evolving fluid–fluid interfaces. The DEM module resolves six degrees of freedom particle motion and accounts for particle contact, cohesion, and rolling resistance. Fully-resolved CFD-DEM coupling is achieved through a fictitious domain immersed boundary (IB) approach. An improved method for enforcing three-phase contact lines with a VOF-IB extension technique is introduced. We present several simulations of binder jet primitive formation using realistic process parameters and material properties. The DEM particle systems are experimentally calibrated to reproduce the cohesion behavior of physical nickel alloy powder feedstocks. We demonstrate the proposed model’s ability to resolve the interdependent fluid and particle dynamics underlying the process by directly comparing simulated primitive granules with one-to-one experimental counterparts obtained from an in-house validation apparatus. This computational framework provides unprecedented insight into the fundamental mechanisms of binder jet 3D printing and presents a versatile new approach for process parameter optimization and defect mitigation that avoids the inherent challenges of experiments.

Study on the factors influencing the performance of dust collection hood of angle grinder based on CFD-DEM simulation

Angle grinders generate a high volume of spark particles during grinding, which pollute the working environment with high dust concentration and create an explosive ignition source due to high temperature sparks. To efficiently collect these grinding spark particles, this study employs a coupled CFD-DEM simulation method to investigate the factors that affect the performance of the dust collection hood of an angle grinder. Firstly, a non-spherical strip grinding spark particle model is constructed based on the characteristics of the grinding spark particles. Then, using ANSYS Fluent software, the CFD-DEM model is employed for simulation calculations. Through statistical analysis of the simulation results, the influence of different parameter factors on the performance of the dust collection hood is determined. The results indicate that the gas flow rate, grinding wheel speed, dust collection hood diameter, suction pipe diameter, and installation angle have a significant impact on the dust control performance of the dust collection hood. The optimal geometric parameters were determined accordingly that strengthened the dust control capacity. This research holds significance in guiding engineering design and mitigating occupational dust hazards in machinery manufacturing.

Design and test of pneumatic dedusting equipment for photovoltaic panels

The multi-stage expansion cavity nozzle working with the vacuum dust suction cavity can suppress the re-entrainment of dust while removing the dust on the photovoltaic panels. But the dimension match and the form of the combination have not been studied adequately. In order to obtain the optimal cleaning performance and the energy consumption, an integrated pneumatic dust removal device is proposed. The internal flow field simulation and CFD-DEM simulation are carried out to optimize the size of the dust removal device and the combination form. Then the dust removal device was produced and the dust removal tests were carried out in dry and wet environments. The test results show that when the inlet pressure is 0.8 MPa, the integrated dust removal device can achieve the highest dust removal rate of 96.51% in dry environment and 85.22% in wet environment. Finally, a pneumatic dedusting equipment with the dust removal device was built and the cleaning performance tests were carried out. The test results show that the photovoltaic power generation efficiency of the entire photovoltaic module was increased by about 16.34%, which verified the feasibility of the pneumatic dedusting equipment.

Simulation of the Classification of Manufactured Sands in the Throat Air Classifier

The scarcity of natural sands has triggered a considerable increase in the consumption of manufactured sands for concrete production. In this regard, the flakiness of the particles and the excess of fines are the main problems that should be addressed when utilizing manufactured sands. The throat classifier is an air classifier designed for the elimination of fine particles (smaller than 75 micrometers) from manufactured sands. The main features of the classifier have been presented in the literature but the mechanism that drives the classification has not been studied in detail. Therefore, this work explores the mechanism of classification of the throat classifier by using CFD-DPM and CFD-DEM simulations. The accuracy and limitations of the methodologies were evaluated by comparing the results against experimental data obtained at pilot scale. The simulations presented fair results in the representation of the airflow and the particle classification inside the throat classifier. Differences between the predictions using the CFD-DPM and the CFD-DEM methodologies under the simulated conditions were found to be negligible. The results of the simulations allowed for a more detailed understanding of the classification mechanism that occurs inside the device and the influence of operational variables on the equipment performance.

Microscopic insights into suction bucket installation in sand: Coupled coarse-grained CFD-DEM simulations

Suction bucket foundations are being used for a wide variety of offshore foundations. However, accurate modeling of its installation remains challenging due to the complexity of soil transportation, in which the soil is typically treated as a continuum and its discrete behavior is neglected. In this paper, the bucket foundation installation in the sand under different installation methods (i.e., jacked and suction-assisted installation) is investigated from a microscopic perspective (i.e., particle scale) based on the three-dimensional coupled computational fluid dynamics (CFD) and coarse-grained discrete element method (CGDEM). It is found that the CFD-CGDEM method can successfully simulate the bucket installation process. Suction-assisted installation results in a significant reduction in the inner skirt friction resistance and end resistance, while the outer skirt friction resistance shows only a minor decrease. During suction-assisted installation, soil loosening inside the bucket contributes more significantly to the soil plug formation compared to the inflow of external soil. Compared to jacked installation, the seepage induces a significant reduction in the effective stress of soil within the interior and below the bucket tip, while it increases the effective stress outside slightly under suction-assisted installation. The work provides an alternative research approach for the suction bucket installation.

CFD-DEM simulation of cyclone self-rotation drying: Particle high-speed self-rotation and heat transfer

Cyclone self-rotation drying (CSRD) has been demonstrated to have the outstanding advantage of low energy consumption in drying field due to the ability of non-phase change separation of liquid in wet particles. Particle high-speed self-rotation are key factors that affect the energy consumption and efficiency of CSRD, but their laws and regulation methods are still unclear. In this study, under the framework of Eulerian-Lagrangian method, Eulerian model and Reynolds Stress Model (RSM) were adopted, and computational fluid dynamics (CFD) and discrete element method (DEM) coupled simulation was established to systematically investigate the effects of operating parameters on sludge particle self-rotation and heat transfer in a 200-mm-diameter CSRD device. The particle self-rotation and revolution speeds were found to decrease with increasing particle size and feeding rate. An average self-rotation speed of 5217.8 rad/s was observed for 1 mm particles at a gas velocity of 10 m/s and a feeding rate of 50 kg/h, when the gas velocity increased to 20 m/s, the self-rotation speed increased about 888.4 rad/s. These operating parameters were also found to affect particle residence time and temperature, smaller particles have better heat transfer performance. This study provides theoretical support for application and optimization of CSRD devices.

Numerical insights into rock–ice avalanche geophysical flow mobility through CFD–DEM simulation

Numerical insights into rock–ice avalanche geophysical flow mobility through CFD–DEM simulation

A critical analysis of the CFD-DEM simulation of pharmaceutical aerosols deposition in upper intra-thoracic airways: Considerations on air flow

A well-corroborated numerical methodology ensuring reproducibility in the modeling of pharmaceutical aerosols deposition in the respiratory system via CFD-DEM simulations within the RANS framework is currently missing. Often, inadequately clarified assumptions and approximations and the lack of evidences on their quantitative impact on the simulated deposition phenomenology, make a direct comparison among the different theoretical studies and the limited number of experiments a very challenging task. Here, with the ultimate goal of providing a critical analysis of some crucial computational aspects of aerosols deposition, we address the issues of velocity fluctuations propagation in the upper intra-thoracic airways and of the persistence of secondary flows using the SimInhale reference benchmark. We complement the investigation by describing how methodologies used to drive the flow through a truncated lung model may affect numerical results and how small discrepancies are observed in velocity profiles when comparing simulations based on different meshing strategies.

Numerical study of fiber deposition in airway replica using CFD-DEM simulation

Numerical study of fiber deposition in airway replica using CFD-DEM simulation

Impact of particle-scale models on CFD-DEM simulations of biomass pyrolysis

The performance of biomass pyrolysis reactors depends on the interplay between chemical reactions, heat and mass transfer, and multiphase flow. These processes occur over a wide range of scales ranging...

NUMERICAL ANALYSIS OF SUFFUSION BEHAVIOR UNDER CYCLIC LOADINGWITH COUPLED CFD-DEM SIMULATION

Cyclic loading has a significant effect on soil properties and seriously threatens geotechnical engineering. However, it remains unclear how cyclic loading affects the suffusion behavior in gap-graded granular soils. In this study, we performed systematic numerical simulations of suffusion in soil samples subjected to triaxial compression coupled with computational fluid dynamics (CFD) and discrete element method (DEM) approaches, i.e., coupled CFD-DEM. The proposed method is able to simulate the suffusion process in gap-graded soils under cyclic loading and reveal the evolution of the fluid fields. The suffusion of gap-graded soil samples was achieved by imposing a downward seepage flow. The results indicated that cyclic loading induces greater erosion mass and fluid velocity during the suffusion process compared to simulations under fixed external forces. The erosion curve can be divided into two stages. In the first stage, the particle loss rate is high, but only lasts for a very short period of time. Then, the particle loss rate slows down and enters the second stage. In this stage, compared to a non-vibrating sample, the sample subjected to cyclic loading still has a large eroded mass, which persists until the end of the simulation. The sensitivity analysis indicated that the first stage of suffusion is more sensitive to an increase in vibration amplitude, whereas the second stage is more responsive to an increase in frequency.

Evaluating the grinding performance of cutter-type disk mills using DEM-CFD simulations with a breakage model

In the recycling process of plastics, grinding is commonly employed as a pre-treatment method to facilitate molding by increasing the specific surface area. A cutter-type disk mill that mainly causes shear forces is expected to be the most efficient for grinding plastics. However, it is necessary to optimize the geometry and operating conditions of the mill. This study aimed to evaluate the grinding performance of different blade geometries in the cutter-type disk mill. To optimize the blade geometry, the discrete element method (DEM) coupled with the computational fluid dynamics (CFD) and a breakage model was employed to simulate plastic particle breakage. The simulations showed that the highest grinding performance was achieved with a grinding blade angle of 45°. Depending on the angle of the grinding blade, the effects of the power acting on the grinding blade and the force acting on the particles varied. According to these results, an appropriate blade geometry in the cutter-type disk mill can be proposed for grinding plastic. This study demonstrated that the DEM-CFD simulations are effective for evaluating the grinding performance and optimizing the blade geometry of the cutter-type disk mill.

CFD-DEM simulation of proppant pack stability during flowback in a rough fracture using supercritical CO2

The destabilization of proppant packs during flowback, leading to undesirable consequences such as choke points (fracture closure near the wellbore) and proppant production, is a critical concern in fracturing operations. Despite its significance, comprehensive investigations into proppant pack stability during flowback remain limited, particularly in supercritical CO2 (Sc-CO2) fracturing. This study addresses this gap by employing an experimentally validated coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) model, integrated with a heat transfer model, to analyze proppant pack stability in Sc-CO2 fracturing near the wellbore. An authentic proppant pack for flowback analysis is generated by simulating proppant pack development during the pumping stage and subsequent compression during the fracture closure stage in a synthetic rough fracture. The findings reveal that the flowback stage can be subdivided into three stages: translation-controlled, rolling-controlled, and stable. Proppant pack stability is intricately governed by factors such as fluid drag force, inter-particle contact force, and pre-flowback pack shape. Due to the reduced fluid drag force, the retained proppant ratios rise under varied conditions: from 47.6% to 95.7% with a decrease in flowback rate from 0.3 m/s to 0.1 m/s, from 50.0% to 67.8% with an increase in fluid temperature from 40 °C to 160 °C, and from 16.5% to 80.8% with an increase in proppant size from 0.4 mm to 0.8 mm. In comparison, due to the increased inter-particle contact force, the retained proppant ratio increases by 16.4% as the closure width increases from 0.15 mm to 0.3 mm. Additionally, a longer proppant pack with a front characterized by a higher inclination angle and curved zone exhibits higher stability during flowback. These insights significantly enhance the understanding of proppant pack stability during flowback, offering crucial guidance for designing Sc-CO2 fracturing processes.

Experimental Investigation and CFD–DEM Simulation of Solids Mixing in Tapered Fluidized Beds

Experimental Investigation and CFD–DEM Simulation of Solids Mixing in Tapered Fluidized Beds