Bed Of Particles Research Articles

Simulation analysis of the effect of a small amount of fine particle added to a slurry on the liquid behavior and forces acting on the main particles

The viscosity of highly concentrated slurries is reduced by adding a small amount of fine particle with the same material of main particles (high concentration ratio particles per total concentration) in the slurries. We investigated how added fine particles affect the liquid behavior and forces acting on the main particles in the slurry by using direct numerical simulations, and we examined one factor that contributes to the viscosity reduction mechanism in highly concentrated slurries containing a small amount of fine particle. The results indicated that whether fine particles are coated (they contact) on the surface or not have little influence on the change in forces acting on the main particles. In highly concentrated slurries containing a small amount of fine particle, there was a large change in the liquid velocity between and around the main particles. From these results, we proposed a possible mechanism to assist in reducing the viscosity of highly concentrated slurries containing a small amount of fine particle. The magnitude and direction of the forces acting on each main particle were non-uniform by adding fine particles, resulting in non-uniform strength within the main particle bed in the slurry, which could facilitate particle bed deformation and assist in reducing the viscosity.

Active intruder motion in a two-dimensional granular medium

We studied an active intruder traversing a two-dimensional granular medium. First, we conducted experiments to analyze the motion of the active intruder within a bed of soft particles distributed throughout a horizontal container. Our observations revealed that the intruder preferentially moved along regions characterized by higher disorder. As a consequence of its motion, and as the intruder repeatedly traversed specific regions, the structure in the vicinity of the path, but also in more distant regions, gradually became more ordered. Additionally, the motion of the intruder tended to be localized in closed paths, with this effect becoming more pronounced at higher particle concentrations. Secondly, we analyzed the behavior of the active intruder within a slightly tilted container and under vibration and shearing conditions, which served to fluidize the granular bed. Our findings indicated that the trajectory of the intruder tended to intersect regions of the granular medium with lower structural order. The overall order and fluidization degrees were found to be the primary influences on the intruder’s penetration length. We used the sixth-bond-orientational order parameter to characterize the local structural aspects of the medium and the mean squared displacement to describe the dynamics of both the intruder and the medium. We conducted an experimental analysis of the ordering of the medium and motion of the intruder using network contact forces in a similar system based on soft gelatin particles. The results of this experimental analysis are consistent with the general results, showing that media with an ordered configuration exhibit more resistance than disordered media.

Combustion characteristics of millimeter-sized aluminum particles in fluidized bed under various O2/CO2/H2O atmospheres

Aluminum is an attractive alternative fuel, but it burns very inefficiently due to the formation of a dense Al2O3 layer which prevents O2 from diffusion to the surface of Al particles. In previous experiments, the combustion of millimeter-sized Al (mAl) particles in the fluidized bed has achieved a substantial increase in the combustion efficiency, but further improvements are still needed. In this study, the effects of reaction atmosphere on the fluidized combustion of mAl particles were investigated. The experiments with different O2/H2O/CO2 concentrations were conducted. The experimental results indicate that the combustion efficiency of mAl particles in fluidized bed increases as the mole fraction of O2, H2O or CO2 increases, and the highest combustion efficiency can reach 38.7%. After the analysis of the oxide film on the surface of aluminum particles, it was found that it is easier to generate the unstable θ-Al2O3 under CO2 atmosphere, and it is easier to generate the unstable γ-Al2O3 and θ-Al2O3 under H2O atmosphere. The unstable Al2O3 film is more likely to be abraded in the fluidized bed, which leads to the effective improvement of the combustion efficiency.

Calibrating the frictional-pressure model from two-fluid simulation of fluidised beds in the defluidisation regime

The two-fluid simulation of a fluidised bed of non-adhesive particles, in which particles are represented as a continuous medium, requires a model for the pressure associated with particle contacts. While closures may be derived in the framework of the kinetic theory of granular flow for short-duration contacts, the frictional pressure associated with enduring particle contacts is generally modelled with an empirical closure involving several free parameters. This article proposes to use the experimental transition between the fluidised-bed and fixed-bed regimes in the determination of these parameters. The prediction of the minimum fluidisation velocity is shown to be governed by the frictional parameters, with either a discrete-element method or a two-fluid model. The shape of the particles, proxied by a sphericity coefficient, also influences the minimum fluidisation velocity. Such dependences of the model prediction can be used to select relevant frictional parameters, by comparison with experimental data or CFD-DEM simulation results.

Vertical velocity of a small sphere in a sheared granular bed

Small particles fall through sheared beds of larger particles in settings ranging from geophysics to industry, but the study of large-to-small size ratios R, spanning the trapping threshold Rt, has been neglected. In simulations of noncohesive spheres for R<Rt, the small-sphere vertical velocity vp first increases with shear rate γ̇ as trapping time decreases, but vp then decreases as velocity fluctuations frustrate downward mobility. For R>Rt, vp is constant at low γ̇, but again decreases at high γ̇. We model these behaviors and discuss analogies with electron transport in solids. Published by the American Physical Society 2024

Impact of flow direction on the isothermal pressure drop through a packed bed of crushed rock – A DEM-CFD approach

Pressure drop plays a crucial role in the design of a packed bed of crushed rock, necessitating a deep understanding of flow behaviour for precise determination of pumping power. This study employs ellipsoidal particles to represent crushed rock, matching the volume and aspect ratio of the sampled rocks. A discrete element model was employed to generate packed beds of ellipsoidal particles, while computational fluid dynamics simulated the flow through the voids in different directions. The model's findings were validated against experimental results from both ellipsoidal particles and crushed rocks. While the ellipsoids effectively capture general flow trends, they underestimate pressure drop through crushed rocks by 5% horizontally and overestimate it by 20% vertically. Consequently, the study proposed a correlation to predict pressure drop in a packed bed using the porous media approach, expressing inertial resistance as a tensor to capture flow direction effects.

Micromechanical origin of heat transfer to granular flow.

Heat transfer across a granular flow is comprised of two resistances in series : near the wall and within the bulk particle bed, neither of which is well understood due to the lack of experimental probes to separate their respective contribution. Here, we use a frequency modulated photothermal technique to separately quantify the thermal resistances in the near-wall and the bulk bed regions of particles in flowing states. Compared to the stationary state, the flowing leads to a higher near-wall resistance and a lower thermal conductivity of bulk beds. Coupled with discrete element method simulation, we show that the near-wall resistance can be explained by particle diffusion in granular flows.

Agglomeration behaviour of various biomass fuels under different air staging conditions in fluidised bed technology for renewable energy applications

The most common technology for thermochemical conversion of solid fuel through the process of gasification, such as coal, varieties of residues from biomass and agriculture are the bubbling fluidised bed or fluidised bed systems. However, there are some disadvantages within these systems including the formation of eutectic mixtures, increased process of melting and bed agglomeration. Hence, the current study aimed to evaluate the agglomeration behaviour of various biomass fuels. Characteristics of five biomass fuels (miscanthus, peanut, straw, domestic wood and industrial wood) in a bubbling fluidised bed (BFB) combustor were studied by SEM-EDX, XRD and XRF analysis of bed materials and ash samples. The influence of bed temperatures on the fuel ash composition and bed particles was evaluated, as well as fuel ash components, their interaction with the particles from the bed sand and morphology of the bed material. The combustion efficiency ranged from 95.5 to 99.5% with the highest value obtained for miscanthus under SA conditions. The peanut and straw had the highest K content, whereas the industrial wood ash contained the highest Ca content compared to other biomasses. The XRF results showed that most of the potassium (K) from the wheat straw biomass was converted to K2O with 19%. No bed agglomeration was noticed without staging-air (WSA) and with staging-air (SA) combustion conditions, even with temperatures up to 850 °C during the testing period. Overall obtained results demonstrated that agglomeration is unlikely expected to be a major problem during fluidised bed combustion of tested biomass fuels.

Trapping of microplastics and other anthropogenic particles in seagrass beds: Ubiquity across a vertical and horizontal sampling gradient

Seagrass beds can trap large amounts of marine debris leading to areas of accumulation, known as ‘sinks’, of anthropogenic particles. While the presence of vegetation can enhance accumulation, less is known about how the trapping effect changes from vegetated to less vegetated patches. To test this, vegetation and sediment were sampled along a vegetation percent cover gradient from the centre of seagrass beds to nearby less vegetated patches. To determine whether trapped particles can lead to increased accumulation in associated fauna, gastropods were also collected from the transects laid across this gradient. Extracted anthropogenic particles were counted and characterised. Particles were detected in all sample types and reached quantifiable limits in at least 50% of sediment and gastropod samples. There was no significant difference in the distribution of particles found in seagrass beds compared to less vegetated patches, suggesting other factors contribute to the trapping efficiency of biogenic habitats besides simply the presence or absence of vegetation.

Data science integrated with computational fluid dynamics for particle collision modeling in fluidized bed

Fluidized beds are critical in numerous industrial applications, including chemical processing and energy production. Accurate modeling of solid particles and fluids within these beds is essential for process optimization and improved efficiency. In this study, we developed a machine learning model to predict the coefficient of restitution (COR) of solid particles in fluidized beds. Four variables—collision velocity, effective temperature, effective mass, and effective elastic modulus—were used in the model. Our dataset comprised 2446 data points from previous literature. We employed self-organizing map (SOM) and artificial neural network (ANN) approaches for data analysis. The initial ANN model, which did not incorporate data clustering, exhibited an impressive coefficient of determination (R-squared) of 0.989, indicating its high accuracy. To enhance the model further, we clustered the data into four groups using SOM and developed separate ANN models for each group. All four models achieved R-squared greater than 0.99, illustrating the effectiveness of data clustering. The resulting model can be integrated into simulation software, such as MFIX, to provide a more precise representation of fluidized bed behavior across various industrial settings. The findings emphasize the potential of machine learning models to enhance fluidized bed simulations, leading to increased efficiency and cost-effectiveness in industrial processes. Future studies should explore the inclusion of additional variables and extend the model's application to different industrial processes. Additionally, incorporating recommendations for optimizing fluidized bed behavior based on the model's predictions would provide valuable insights for process engineers.

Fluidized bed hydrodynamics under variable air inlet configurations to enhance gasification reactor efficiency: Computational study

This study employs diverse strategies to enhance motion dynamics within the reactor, with a specific focus on the critical geometric parameter of air nozzle configuration. Methodical analysis of various air nozzle angles, 0°, 45o, and 90° relative to the horizontal bottom line is undertaken to discern their influence on these key parameters throughout multiple stages during the recorded flow duration. A CFD model of the physical model is constructed and solved using ANSYS software. Parameters scrutinized include the longitudinal and lateral distribution of particle volume fraction, alongside radial and axial velocities of particles. The results emphasize the significant impact of air-feeding orientation on both radial and axial particle velocities. Notably, 45° air nozzle angle is the best orientation for the fluidized bed reactor displaying maximal values in particle volume fraction fluctuations and bed height. Furthermore, peak values for radial and axial velocity persist consistently throughout the entire flow duration.

Charging kinetics of a vibrated bed of particles by numerical simulations and experiments

Through particle dynamics simulations and experiments, we investigate the charging kinetics of a granular bed in a vibrating cell. The numerical method is based on a theoretical model combining an equation for charge transfer at the particle scale with a theoretical model of charge relaxation. Simultaneously, experiments are carried out to calibrate and validate the numerical model using a vibrated cell with glass beads. Specific charge per unit mass induced by vibrations initially increases before leveling off. Saturation specific charge and charging characteristic time decrease with increasing bed mass. Data collapse onto a master curve is observed when normalizing specific charges and times. At the particle scale, we find that charge saturation results from the balance between charge transfer and relaxation. Saturation specific charge correlates with the relative rate of collisions between particles and the vibrating plate. We introduce a simple expression for the average ballistic time based on single-particle dynamics and a restitution coefficient dependent on bed mass. The characteristic time is proportional to the ballistic time and decreases with increasing bed mass due to more inelastic collisions between particles.

Numerical Analysis of Non-Sphericity of Particles of Powder Material and their Effect on Packing Structure for Concentrated Solar Power Applications

Concentrated solar power technology represents a novel approach to generating solar power, characterized by high solar radiation density and uninterrupted operation. To store thermal energy and extend system operating hours, concentrated solar power systems rely on thermal energy storage. Selecting the appropriate heat storage media is crucial for designing a cost-efficient and straightforward system capable of withstanding high processing conditions. Among many powder materials, bauxite powder stands out as alternatives to conventional molten salt for thermal storage media due to its widespread availability and suitability for operating conditions. Particle shape, particularly its sphericity, plays a vital role in efficiently packing particles which directly affects to heat transfer properties. To investigate this effect, three samples of particles with different shape were formed: spheres, ellipses, and cylinders using Discrete Element Method with equal volume and material properties, and only variation of their sphericity factors. The study focused on the analysis of the porosity of the packed bed of particles with different shapes and its influence on the packing structure properties. The analysis of local packing fraction revealed that elliptical and cylindrical particles samples exhibited reduced heap formation and a more uniform distribution along z direction during vertical packing. The coordination number and radial distribution function analyses for these non-spherical particles showed a greater number of contacts between particles and disordered distribution of particles due to mechanical interlocking of non-spherical particles. The results indicated that the deviation of sphericity has a positive impact on the denser packing of particles generated more contacts and higher local packing fraction.

Vulnerability of Thermal Energy Storage Lining Material to Erosion Induced by Particulate Flow in Concentrated Solar Power Tower Systems.

Researchers from all around the world have been paying close attention to particle-based power tower technologies. On the King Saud University campus in the Kingdom of Saudi Arabia, the first integrated gas turbine-solar particle heating hybrid system has been realized. In this study, two different types of experiments were carried out to examine how susceptible prospective liner materials for thermal energy storage tanks were to erosion. An accelerated direct-impact test with high particulate temperature was the first experiment. A low-velocity mass-flow test was the second experiment, and it closely mimicked the flow circumstances in a real thermal energy storage tank. The tests were conducted on bare insulating fire bricks (IFBs) and IFBs coated with Tuffcrete 47, Matrigun 25 ACX, and Tuffcrete 60 M. The latter three lining materials were high-temperature-resilient materials made by Allied Mineral Products Inc. (AMP) (Columbus, OH, USA). The results showed that although IFBs coated with AMP materials worked well in this test, the accelerated direct-impact test significantly reduced the bulk of the bare IFB. As a result, lining substances must be added to the surface of IFBs to increase their strength and protection because they cannot be used in situations where particles directly impact their surface. On the other hand, the findings of the 60 h cold-particle mass-flow test revealed that the IFBs were not significantly eroded. Additionally, it was discovered that the degree of erosion on the samples of bare IFB was unaffected by the height of the particle bed.

Understanding cohesive zone behaviour of blast furnace based on computed tomography flow modelling in a fused bed of ferrous and coke particles

Performance of ironmaking blast furnace systems critically depends on the permeability of the cohesive zone which involves flow of reducing gas through a packed bed of fused ferrous and coke particles at high temperature. This study systematically investigated the effect of operating temperature on bed permeability for two different ferrous burdens - pellets, and pellets-sinter mixture supported on coke particles. To quantify the structural changes in the bed, interrupted tests at various temperatures were conducted and bed porosity was estimated using synchrotron X-ray computed tomography (CT) technique. Bed porosity showed decreasing trends with increasing temperature. A CT image based computational flow dynamics (CFD) model was developed which showed linearly decreasing trends of bed permeability parameter with increasing temperature indicating a significant loss of bed permeability in the high temperature cases. This behaviour was more pronounced for the pure pellet case compared to the mixed burden case.

Unified gas-kinetic wave–particle method for polydisperse gas–solid particle multiphase flow

The gas-particle flow with multiple dispersed solid phases is associated with a complicated multiphase flow dynamics. In this paper, a unified algorithm is proposed for the gas-particle multiphase flow. The gas-kinetic scheme (GKS) is used to simulate the gas phase and the multiscale unified gas-kinetic wave–particle (UGKWP) method is developed for the multiple dispersed solid particle phase. For each disperse solid particle phase, the decomposition of deterministic wave and statistic particle in UGKWP is based on the local cell's Knudsen number. The method for solid particle phase can become the Eulerian fluid approach at the small cell's Knudsen number and the Lagrangian particle approach at the large cell's Knudsen number. This becomes an optimized algorithm for simulating dispersed particle phases with a large variation of Knudsen numbers due to different physical properties of the individual particle phase, such as the particle diameter, material density, etc. The GKS-UGKWP method for gas-particle flow unifies the Eulerian–Eulerian and Eulerian–Lagrangian methods. The particle and wave decompositions for the solid particle phase and their coupled evolution in UGKWP come from the consideration to balance the physical accuracy and numerical efficiency. Two cases of a gas–solid fluidization system, i.e. one circulating fluidized bed and one turbulent fluidized bed, are simulated. The typical flow structures of the fluidized particles are captured, and the time-averaged variables of the flow field agree well with the experimental measurements. In addition, the shock particle–bed interaction is studied by the proposed method, which validates the algorithm for the polydisperse gas-particle system in the highly compressible case, where the dynamic evolution process of the particle cloud is investigated.

On the modelling of the effective longitudinal diffusion in bi-continuous chromatographic beds

We report on the possibility to extend to bi-continuous packings the two models for the effective longitudinal diffusion Deff, or B-term band broadening, recently proposed for discontinuous chromatographic beds. In bi-continuous packings, like monolithic columns, solutes experience a connected end-to-end pathway in both the mobile and stationary zones, as opposed to discontinuous packings, wherein the stationary adsorptive zone is distributed over a set of isolated elements. Since it is unclear whether a densely packed bed of spherical particles should be treated as a continuous or a bi-continuous medium, this extension is also crucial to fully understand the behaviour of packed particle beds. The proposed models for the effective longitudinal diffusion Deff originate from the adoption of the Two Zone Moment Analysis (TZMA) method by which Deff can be expressed as a linear combination of two essential quantities γm and γs, referred to as effective zone-diffusion factors. In the present work we propose two analytical models for γm and γs that now cover both the discontinuous and the bi-continuous case. To validate the theory, several bi-continuous packings are investigated, including the tetrahedral skeleton model (TSM), six different Triple Periodic Minimal Surface (TPMS) monoliths and randomly packed beds of spheres. For all of these, the models provide highly accurate results for Deff over a wide range of porosities and zone retention factors k″. The comparison with literature experimental data for both monolithic silica columns and columns packed with fully porous and porous-shell particles is also presented.

A Volume-Averaged Hyperbolic System of Governing Equations for Granular Turbulent Flow Modeling With Phase Change

Abstract A formulation is developed using volume-averaging and the concept of added mass to derive a hyperbolic system of governing equations for modeling turbulent, dense granular flows. The large eddy simulations (LES) framework is employed for the fluid phase, whereas the solid phase equations are based on enlarged Kinetic Theory concepts. To obtain the LES equations, the volume-averaged equations are filtered and the filtered terms not directly computable from the LES solution are generically modeled. Additionally, the pseudo-turbulent kinetic energy (PTKE) is included in the formulation and it is shown how its contribution is distinct from turbulence and leads to different terms that must be modeled in the conservation equations. Volume-averaging of the continuity, momentum and energy equations result in many integrals that are used to rigorously define the meaning of terms that have only been included heuristically in existing formulations. Simulations with this model are conducted in a configuration representing the interaction of a turbulent supersonic jet with a bed of solid particles. The results are analyzed to demonstrate hyperbolicity. Comparisons of results from a model including PTKE and one excluding it show that the inclusion of PTKE has no role in bestowing hyperbolicity to the model, and furthermore does not affect the macroscopic aspects of the crater. Comparisons between results obtained with a hyperbolic model and a model that is hyperbolic everywhere except in regions of particle/fluid interaction show that the macroscopic crater aspects are different, affecting the crater shape and topography.

Shear Strength and Consolidation Behaviour of Kaolin Clay Reinforced with a Granular Column Backfilled with Crushed Waste Glass

Granular columns are commonly used for ground improvement. However, minimal research is presently available on the effect of backfill particle size on the geotechnical performance of granular column-reinforced soil. Geo-environmentally, using crushed waste glass (CWG) as a sustainable replacement for depleting traditional construction sands could offer a cleaner feedstock to backfill granular columns while helping recycle growing stockpiles of waste glass, potentially supporting the circular economy transition and decarbonisation of the construction industry. Given these multi-pronged motivations, this study investigated the shear strength and consolidation behaviour of kaolin reinforced with a CWG granular column. Three different particle size ranges (PSR) of CWG were discretely used to install a granular column in the kaolin bed, including fine (0.50–1.0 mm), medium (1.0–1.7 mm) and coarse (1.7–3.35 mm) particles with median particle sizes of 0.78 mm, 1.42 mm and 2.30 mm, respectively. The geocomposite containing a medium CWG column showed the highest increase in friction angle, increasing from 14.0° for kaolin only specimens to 20.7° for the geocomposites. Similarly, the consolidation behaviour of reinforced kaolin (geocomposites) was typically superior to that of kaolin only specimens. Notably, installing a coarse, medium or fine CWG column decreased the average compression index (Cc) of the geocomposites by almost 17%, 35% or 50%, respectively, compared to that of the kaolin only specimens. Given the promising results of this initial study, some suggestions are provided for future studies on assessing the application of CWG as an alternative backfill and sustainable geomaterial in granular column construction.Video abstractThis internationally-partnered Video highlights the findings of the research study, indicating that crushed waste glass (CWG) could potentially serve as a sustainable geomaterial and be used as a replacement for traditional construction sand to backfill granular columns in clayey soils for ground improvement, helping reduce the unsustainable exploitation of sand resources and increasing waste glass recycling, potentially supporting the paradigm shift to a circular economy and contributing to decarbonisation of the construction industry.EwdaqE4KyyTKvkX4_pnUt6Supplementary material 1 (MP4 3737519 kb)

Shaping technical catalyst particles in a bottom-spray fluidized bed

This work aims to elucidate the particle growth mechanism during agglomeration using a bottom-spray fluidized bed process to produce technical catalysts. The influences of the fundamental operating parameters of the granulation process were investigated through (i) experiments in a newly designed small-scale bottom-spray fluidized bed reactor, (ii) morphological characterization of the catalytic particles produced, (iii) dimensionless number analysis, and (iv) principal component analysis. These results could define the growth stage as dust formation, seed formation, agglomeration, and dust integration or layering. The particle growth mechanism results from the complex interplay of several effects and forces (mass transfer, viscous force, inertial force, surface tension, and gravity), and the prevailing growth stage can be linked with the Weber (We) and capillary (Ca) numbers (i.e., low values of We = 5.7 and Ca = 1.4 leads to layering growth and high values of We = 19.1 and Ca = 7.1 results in dust formation).