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In the present study, a new disturbing rotary centrifugal classifier was designed and a method was proposed to characterize its pressure signals. The models for evaluating the classification effects were established based on multi-zones. It was found that the flow field, processing parameters, and material properties significantly affected on the particle force and classification performance. The pressure with high amplitude and energy analyzed using Hilbert-Huang Transform (HHT) concentrated within 200–400 Hz, and the screening cage facilitated energy transfer to lower frequency bands. Correlation analysis demonstrated the correlation coefficients (A5 and A6) between adjacent measurement points increased with frequency, further enhanced by the screening cage. The flow field of simulation was characterized by a low-pressure, high-velocity gradient at the center and a high-pressure, low-velocity gradient at the sidewalls and the gas velocity and flow for experiment achieved the maximum at z = 0.50 m, while the magnitude of pressure change was significant at the inlet end and discharge end, where the velocity gradient and pressure drop had the same trend and small errors for experiments and simulation. The flow field affected the competing relationship between centrifugal and drag forces on the particles with different kinematic behavior during the classification process. The errors between the predicted values of the theoretical, simulated, and experimental cut particle size models and the true values were all within 10 %, based on which the multi-zone classification efficiency model applicable to the disturbing centrifugal classifier was established, and it was found that the models all had high prediction accuracy and suitability. The article delves into the correlation between pressure signals, flow field characteristics and particle behavior, aiming to provide an important reference for the internal flow field and classification performance of air classifiers. [Display omitted] • Analyzed the time-frequency characteristic of pressure signals by HHT. • Measured the correlation degree of neighboring signals using correlation analysis. • Studied the spatial flow field characteristics for simulation and experiments. • Theoretical, simulate and experimental models of cut particle size were established. • Predicted and compared the multi-zone classification efficiency model. [ABSTRACT FROM AUTHOR]

Polydisperse particle feed into centrifugal slurry complicates hydraulic performance and wall erosion but is poorly understood. This paper presents a numerical study of a centrifugal slurry pump, focusing on the effect of particle size distribution (PSD) using the combined computational fluid dynamics and discrete element method (CFD-DEM). It incorporates rigid impeller rotation and wall erosion. On this basis, the hydraulic and erosion model validity is verified by clear water performance and jet erosion test, respectively. Additionally, this CFD-DEM model is compared with the dense discrete phase model (DDPM), demonstrating more precise erosion prediction as its fully resolved particle-particle interactions. Generally, total pump erosion severity intensifies when the PSD is broadened. Compartment-wise, it indicates the necessity of tailoring flow structure to enlarge drag force, therefore, mitigate particle aggregation in the impeller. This in-house CFD-DEM model is promising for addressing particle-fluid flow problems in centrifugal pumps or coupling with data driven method. [Display omitted] • Erosion characteristics to particle-fluid interaction force is elaborated. • Particles accumulate at the trailing side of blade in rotation of impeller. • Increment in particle size distribution (PSD) intensifies the total pump erosion. • Compartment-wise erosion is greatly influenced by the equivalent particle size. [ABSTRACT FROM AUTHOR]

In this study, a drag force model of irregular-shaped particles in gas-solid flows is investigated using neural network approaches. Pre-developed variational autoencoder, multi-layer perceptron model, and transpose convolutional neural-network model are utilized to obtain intermediate parameters of a pair-wise interaction point-particle (PIEP) model. These parameters are utilized to predict individual drag force coefficients of polydisperse, particulate flows. To apply the PIEP-based model to medium-concentration flows, the average drag force coefficients are obtained through an in-house particle-resolved direct numerical simulation, and a regressed model is developed to predict solid volume fraction factors. With the regression model, the PIEP-based model using the neural-network approaches shows good prediction in particulate systems from low to intermediate concentrations. This study provides computationally efficient models of practical, realistic particulate systems for large scale fluid dynamics simulation, in that it allows predicting the drag forces of polydisperse particles with a small amount of data. [Display omitted] • Superposition model simulates polydisperse array of irregular-shaped particles. • Neural networks predict geometrical features, single drag force and flow fields. • Direct numerical simulation is utilized to formulate solid volume fraction factors. [ABSTRACT FROM AUTHOR]

This paper aims to improve existing models for drag, lift, and pitching torque coefficients of cylindrical disc particles with a wider range of aspect ratios and particle Reynolds numbers. The full body-fitted direct numerical simulations (DNS) are carried out for three-dimensional flow past cylindrical discs in order to quantify the coefficients at aspect ratios from 0.2 to 0.6, incidence angles from 0°to 90°, and Reynolds numbers from 0.1 to 300. The CFD results are validated against the aerodynamic coefficients of both spherical and non-spherical particles presented in the literature. A full set of new correlations for the coefficients, dependent on aspect ratio, incidence angle, and Reynolds number, is further derived according to the CFD predicted data. The results show that the new correlations have a promising performance for the disc particles considered in this study. [Display omitted] • CFD simulations are performed for drag, lift, and pitching torque coefficients. • A complete set of correlations for C D , C L , and C T is proposed. • Proposed correlations work well outside the Stokes regime. • The correlation predictions agree with the CFD simulations. [ABSTRACT FROM AUTHOR]

A bead mill is often employed in powder processes. In the bead mill, the bead-particles move rapidly under high shear rate due to the moving structures. The discrete element method (DEM) coupled with the computational fluid dynamics (CFD) has been applied to simulate the bead-particle behavior for the optimization of the bead mill design and operating conditions. However, the existing DEM-CFD method faces essential problems regarding the substantial limit of the number of computational particles, stable calculations, and modeling of rapidly moving structures. To solve these problems, we newly investigate a numerical model combining the coarse-grained DEM-CFD, an implicit algorithm for the drag force term, and a scalar field-based wall boundary in the calculation of a bead mill commonly employed in industrial powder processes. In this study, our proposed model is shown to successfully simulate the macroscopic behavior of the bead-particles through the validation test of the coarse-grained DEM-CFD simulation in the bead mill system. Specifically, the macroscopic characteristics such as the particle location, the particle velocity, and total kinetic energy, are shown to agree well between the original particle system and coarse-grained particle systems. Consequently, this study illustrates the combination of the coarse-grained DEM-CFD, an implicit algorithm for the drag force term, and the scalar field-based wall boundary is essential for simulating the typically industrial bead mill, where an enormous number of bead-particles should be calculated in liquid under high shear rate. [Display omitted] • We newly investigate a numerical model to simulate an industrial bead mill. • The coarse-grained DEM can perform the efficient simulation of the bead mill. • An implicit algorithm must be employed for the stable computation. • Scalar field-based wall boundary is crucial to simulate the moving structure. • Combination of the above models is essential for the simulation of the bead mill. [ABSTRACT FROM AUTHOR]

Solid-fluid multiphase systems are ubiquitous in many chemical, pharmaceutical, and energy based applications. These flows are challenging to study experimentally, thus several numerical simulation techniques have been developed. In this paper we use Particle Resolved Simulations (PRS) combined with Deep Learning (DL) to predict drag forces on each particle in suspensions of ellipsoidal particles for use in lower fidelity Euler-Lagrange and Euler-Euler simulations. Suspensions with solid fraction of 0.1, 0.2 and 0.3 are investigated at Reynolds numbers of 10, 50, 100 and 200. A UNet architecture is used to predict the velocity and pressure fields and a CNN is used to predict the drag forces. It is shown that drag force predictions using the predicted velocity and pressure fields give more accurate results than predictions that only use geometric information. [Display omitted] • Deep learning used to predict fluid drag forces in suspension of ellipsoids. • UNet architecture is used to predict interstitial flow and CNN to predict drag force. • Model accuracy evaluated for different input features and supervisions. • Flow predictions superior when informed by location of distant particles. • Drag force predictions are superior when informed by interstitial flow. [ABSTRACT FROM AUTHOR]

Resonance Acoustic Mixing® (RAM) technology applies an external low-frequency vertical harmonic vibration to mix and deagglomerate fine and ultrafine granular materials. However, although this system is used for various applications, its mechanism is yet not well understood. To address this gap in the knowledge, in this study, a continuum model of powder in a low-frequency vertical harmonic vibration container was established, and spectral proper orthogonal decomposition was used to analyse the slip velocity. The mechanism of fine particle deagglomeration with vertical harmonic vibration is proposed. The slip velocity at the interface between the particles and air has a significant periodic character and produces a persistent drag force on the particles. As the vibrational excitation frequency increases, the bandwidth of the slip velocity becomes narrower and the peak frequency becomes equal to the vibrational frequency. The drag force produced by the periodic slip velocity is the main contribution to the deagglomeration force, which needs to overcome aggregation forces (e.g., van der Waals force). The strength of the deagglomeration force determines the overall deagglomeration performance and the particle size distribution of the agglomerates. [Display omitted] • The possible mechanism of deagglomeration of fine powder in RAM is proposed. • The proportion change model of different size agglomeration in RAM is established. • The spectral characteristics of slip velocity are studied by SPOD. [ABSTRACT FROM AUTHOR]

In the present work, the hydrodynamics behavior of a 3D small-scale cold flow modeling of a gas-solid tapered fluidized bed is evaluated with the Eulerian-Eulerian two-fluid modeling (TFM) approach. The sensitivity of different modeling parameters, including lift and virtual mass forces, viscous force, gas-solid drag force, granular temperature, granular viscosity, granular pressure, particle-wall specularity coefficient, particle-particle restitution coefficient, and particle-wall restitution coefficient, are systematically investigated to optimize the performance of the present numerical model. The results from different sensitivity analyses reveal that the gas-particle drag force is a more important force to resolve the correct time-averaged axial and radial solids holdup profiles of the tapered fluidized bed than the other investigated parameters. The highest accuracy possible from simulations is achieved from the Gibilaro drag model followed by the Arastoopour and EMMS/bubbling models. In contrast, all other drag models over-predict the gas-particle interaction force. The assessment of the lift and virtual mass forces, viscous force, granular temperature, granular viscosity, granular pressure, and particle-wall restitution coefficient results reveal that these parameters are less critical for the numerical simulations of the tapered fluidized bed than the gas-solid drag force. However, the assessment of particle-wall specularity coefficient and particle-particle restitution coefficient reveals that adjusting these parameters in the numerical simulations is helpful to achieve a better agreement between the experimental data and model results. For the higher gas flow rate, the current work shows that a better agreement can be achieved by tuning the parameter values in the standard sub-models than the previously published TFM studies. Meanwhile, for the lower gas flow rate, the accuracy of the present work is slightly lower than the previously published work but acceptable with the experimental measurements. The current work has an advantage over the previously published work in terms of lower computational effort by using the simplified geometry and mean particle diameter assumptions. [Display omitted] • We simulated a 3D tapered fluidized bed reactor using the TFM approach. • We performed the sensitivity analysis of key modeling parameters and sub-models. • Drag force has a much greater impact on the hydrodynamics than the other forces. • We implemented the BVK, EMMS/bubbling, and Arastoopour drag models through UDFs. • We optimized the performance of the TFM based on its sensitivity analysis. [ABSTRACT FROM AUTHOR]

This study investigates the movement behavior of particles of dissimilar morphology in the powder bed in Laser Powder Bed Fusion. Gas atomized (GA) and water atomized (WA) low alloy steel powders were employed to study their motion around the laser scan path. Particle velocities, entrainment distances and denudation zones were measured for both powders using high-speed imaging. The entrainment of GA powder particles in front of the laser beam towards the process area was initiated 1.6 mm from the edge of the melt pool, whereas the distance was 0.6–0.8 mm for the WA powder. The differences in observed behavior were related to the variations in particle shape of the two types of powder. The processing of WA powder resulted in a 16% narrower denudation zone (for a low volumetric energy density) compared to GA powder. However, the denudation width difference decreased with increasing volumetric energy density, most likely due to a steeper pressure gradient in the process area which diminishes the impact of powder shape. X-ray computed microtomography was utilized to estimate the drag force acting on the powder particles of various morphologies. The results showed that the radial drag force exerted on GA powder was 64% greater than when using WA powder. Moreover, if the WA powder particles were of elongated shape the drag force decreased by almost an order of magnitude, demonstrating the importance of the particle's morphology in the process dynamics. [Display omitted] • Movement behavior of particles of dissimilar morphology was studied • Water atomized powder particles had reduced mobility in the powder bed • Processing of water atomized powder resulted in a narrower denudation zone • 50 % less particle entrainment was observed in the water atomized powder bed • Drag force varies depending on the particle shape and position in the powder bed [ABSTRACT FROM AUTHOR]

The gravel granular filter has been widely used to eliminate the strong shock waves induced by deliberated and occasional explosions. The modelling of shock wave propagation and attenuation in the gravel granular filter is still not well resolved and is a topic of current research. In this study, a new three-dimensional mesoscopic model of gravel granular filter is presented. This involves establishing the geometric model of three-dimensional gravel particles with the consideration of random shape based on the Voronoi algorithm, then generating the corresponding FE mesh based on the mapping grid algorithm and finally precisely controlling the porosity by applying a given displacement load. The three-dimensional mesoscopic model is then validated by numerically simulating two field tests on shock wave propagation and attenuation in a gravel granular filter. Detailed analysis of numerical simulations demonstrates that the drag force between gaseous phase and solid filter and the multiple complex reflection and diffraction between the particles are the main causes of the attenuation of shock wave with low amplitude. Finally, parametric study on the five dominant characteristics of filter, i.e., the particle shape, filter porosity, filter length, particle size and particle wave impedance are conducted. It is found that the particle shape, porosity, and wave impedance of filter have a strong influence on the capability of shock wave attenuation, and the filter length has limited influence beyond a critical optimal length, while the particle size has negligible effect. [Display omitted] • A new 3D mesoscopic model of gravel granular filter is proposed. • The mesoscopic model can predict shock wave attenuation proved by two field tests. • The drag force and complex reflection and diffraction are main causes of shock wave. • Porosity, wave impedance and particle shape have strong effects on wave attenuation. [ABSTRACT FROM AUTHOR]

A scale-independent modeling method for filtered drag force is proposed for coarse-grid simulation of fluidized gas-solid flows based on the fine-grid data generated using kinetic theory-based two-fluid method in periodic sedimentation systems. In the modeling process, the filtered solid volume fraction at a larger scale whose side length is three times of the filter size is introduced as a new marker. New developed closures show an excellent performance in a priori test, and exhibit a fairly good agreement with the fine-grid data and the experimental data in a posteriori test for three typical fluidized regimes including bubbling, turbulent and fast fluidized beds. Furthermore, the available correction methods to consider the effect of the material properties via adding a multiplicative factor are tested. The results show that these correction methods are not suitable for the considered cases. [Display omitted] • A scale-independent modeling method for filtered drag is developed. • The proposed models show excellent performance in a priori analysis. • Validations of the new model show good performance in three regimes. • Material property corrections by multiplying a coefficient are tested. [ABSTRACT FROM AUTHOR]

Unresolved and semi-resolved CFD-DEM coupling are frequently used for modeling particulate flows due to their high efficiency and satisfying accuracy. The grid size (in unresolved CFD-DEM) and smoothing distance (in semi-resolved CFD-DEM) are usually around three times of the particle diameter so as to properly reproduce the background flow field. An over-estimation of the grid size or smoothing distance can lead to low-fidelity flow fields, while under-estimations of these parameters can produce an inaccurate drag force. Therefore in practices, the size ratio is usually empirical, and how does it vary with cases remains unclear. In this paper, we provide an approach to identify the most suitable grid size or smoothing distance in coupled CFD-DEM. Firstly, resolved simulations based on immersed boundary method (IBM) are conducted to compute particles' drag forces. The obtained forces are then compared with those calculated by force models with certain smoothing lengths to identify an optimal smoothing length or effective grid size. During this process, integral scale of each case is also computed. Finally, linearity between integral length and the optimal smoothing distance or grid size is found. This correlation can offer guidance to CFD-DEM modeling in future and provide insights for novel drag force models. [Display omitted] • Optimal grid size in un-resolved CFD-DEM coupling is identified. • Optimal smoothing distance in semi-resolved CFD-DEM coupling is identified. • Optimal grid size and smoothing distance are determined by flow's integral scale. • Quantitative relation of the ratio of grid size to particle diameter is found. • Quantitative relation of ratio of smoothing distance to particle diameter is found. [ABSTRACT FROM AUTHOR]

While scholars are aware of the suction force of particles (F Dn) in gas-solid flow, until recently, most researchers have considered the drag force (F D) to be F Dn , and there are few application functions for the calculation of F Dn ; this will affect the design of air-suction seeders, check valves, or other machines based on particle absorption. Therefore, it is necessary to re-build an applicable function of F Dn and verify the equivalence between F Dn and F D. In the present study, the empirical formula of F Dn , which includes the suction hole diameter (D), particle diameter (d p), distance from the particle center to the suction hole (L p), pressure difference (ΔP), gas density (ρ g), and gas viscosity (μ g), is established via dimensional analysis, and the application scope is 0.571 ≤ D/d p ≤ 1, 0.5 ≤ L/d p ≤ 0.634, and 3000 Pa ≤ ΔP ≤ 5000 Pa. Some conjectures are provided based on the comparison of the results of CFD simulations and experiments. For instance, F Dn may be a combination of multiple forces, one of which is the dominant force F D. This research introduces a new method and device for measuring F Dn for use by other researchers, and contributes to the existing research on particle absorption. [Display omitted] • The empirical formula of suction force on spherical particles in suction flow is constructed. • The applicable condition of the empirical formula is 0.571 ≤ D/d p ≤ 1, 0.5 ≤ L p /d p ≤ 0.634, and 3000 Pa ≤ ΔP ≤ 6000 Pa. • The suction force may include the drag force, and the drag force is the dominant force. • The empirical formula is a piecewise function of D/d p. [ABSTRACT FROM AUTHOR]

Planting performance is essential for wheat seeders and reliable seed germination. The seed-filling effect is also important in the sowing performance. In this study, a self-suction wheat shooting device was developed to improve the seed-filling performance. In specific, the shooting device structure was optimized, in which negative pressure was generated in the inner cavity of the device. A DEM-CFD coupling simulation experiment was conducted to investigate the seed-filling and shooting performance. The effect of three working parameters (rotational speed of shooting device, window length and window width of directional seed delivery wheel) on the coefficient of variation of the seed-filling performance (CVSF), average shooting speed (ASS), average shooting depth (ASD) and drag force (DF) were analyzed. Afterward, a validation experiment was conducted to investigate the shooting performance of the self-suction shooting device. The results showed that the shooting performance of the self-suction device under optimized operation parameters could fully meet the shooting requirements of winter wheat in the North China plain. In specific, the coefficient of variation of the seed amount (CVSA), ASD and ASS of self-suction shooting device were 7.1%, 30.9 mm and 33.5 m/s at the rotational speed, window length and window width were 1200 rpm, 35 mm and 60 mm, respectively. [Display omitted] • A "seed–air-soil" coupling model is simulated by DEM–CFD approach. • The seed motion characteristics and shooting performance are described. • The characteristic of drag force in self-suction device is conducted. • A comparison of self-suction and mechanical shooting device is conducted. [ABSTRACT FROM AUTHOR]

To enable the mechanistic description of the mixing of larger particles in gas-fluidized beds in models (e.g. fuel particles in combustors), knowledge about the rheology of the bed emulsion is required. Here, it is crucial to determine the drag on large fuel-alike particles. This work presents the experimental work on the fate of 13 different solid spheres falling or rising through a bed of air and glass beads at minimum fluidization. The trajectories of the tracer are highly resolved (sampling rate of 200 Hz) by means of magnetic particle tracking, this previously unmet accuracy allows disclosing the complex rheological behavior of gas-solids fluidized bed emulsions in terms of drag on immersed objects. The trajectories reveal that none of the tracers reach terminal velocity during their fall and rise through the bed. The shear stress is obtained through the drag force by solving the equation of motion for the tracer. The data reveal particularities of the bed rheology and clear differences of its effect on rising and falling particles. When studying the shear stress over the characteristic shear rate of each tracer, it can be seen that the stress of the bed on the tracers is dominated by a yield stress, with a somewhat smaller contribution of the shear stress. For rising tracers this last contribution is almost negligible. The falling tracers show strong interaction with the bed emulsion, resulting in a fluctuating shear stress, which increases with tracer size and density. The stagnation of some tracers at low shear rates reveals a viscoplastic behavior of the bed emulsion, exhibiting a typical yield stress that showing a clear dependence on the tracer diameter and buoyant density. The concept of yield gravity is used in order to introduce a normalized shear stress which provides additional verification of the experimental observations in relation to the influence of tracer size and relative density on the shear stress. [Display omitted] • Highly resolved tracer trajectories reveal non-Newtonian rheology of gas-fluidized bed. • Falling sphere experiments in gas-fluidized beds reveal viscoplastic rheology. • Rising tracers show no dependence on the shear rate. • Yield stress on the spherical tracer is dependent on the tracer properties (diameter, density). • Contribution of yield stress is higher than the shear stress dependence on the shear rate. [ABSTRACT FROM AUTHOR]

The modeling of the fluidization or sedimentation velocity of a suspension of solid particles is revisited by examining experiments conducted in either a liquid or a gas. A general expression is found in the case of negligible fluid inertia, i.e. at low Reynolds or Archimedes number. It is built as the product of the velocity of an isolated particle by three non-dimensional corrections that each takes into account a specific physical mechanism. The first correction reflects the variation of the buoyancy with the particle concentration. The second correction describes how the drag force increases with the concentration in case of negligible particle inertia. The third one accounts for the further increase of the drag when the particle inertia is increased. Remarkably, each correction only relies on a single of the three independent non-dimensional groups that control the problem: (1) the particle volume fraction Φ s ; (2) the ratio Φ s /Φ pack where Φ pack is the bed packing concentration; (3) the Stokes number S t 0 , which characterizes the inertia of the particles and controls their agitation. Moreover, the onset of the instability that separates the homogeneous regime from the heterogeneous one is found to be controlled similarly by the Stokes number. Empirical expressions of the corrections are given, which provide a reliable tool to predict fluidization and sedimentation velocities for all values of the three non-dimensional numbers. The present results emphasize the crucial role of particle inertia, which is often disregarded in previous modeling approaches, such as that of Richardson and Zaki. [Display omitted] • Modeling the fluidization/ sedimentation velocity U of particulate suspensions • Proposing a general expression of U for cases of negligible fluid inertia • Building this expression as the product of the Stokes velocity by 3 corrections • Explaining why some classical approaches are not valid in the homogeneous regime • Modeling the boundaries of the homogeneous regime of suspensions [ABSTRACT FROM AUTHOR]

When the concentration of porous particles reaches a certain level, the interactions between the particles can't be ignored. Therefore, this paper numerically investigated the interactions between two porous particles using the lattice Boltzmann method. In this paper, two-dimensional steady flow and heat transfer around and through two porous particles with the same diameters (D) was studied numerically. The effects of Reynolds number (Re), Darcy number (Da), center-to-center distance (expressed as dimensionless form L/D), angle between two porous particles (β) and particles with different permeability on the flow and heat transfer characteristics were investigated in detail. The investigated ranges of the parameters were 10 ≤ Re ≤ 40, 10−6 ≤ Da ≤ 10−2, D ≤ L ≤ 4 D and 0° ≤ β ≤ 90°. It is observed that these parameters have significant effects on the flow and temperature fields, drag coefficient and average Nusselt number. The drag coefficient and average Nusselt number of the leading particle (P1) is much larger than those of the trailing particle (P2) in most instances. And the two porous particles show different change tendency to the same changes of these parameters. The effects of Da on P1 are more prominent compared with P2 while the effects of L / D on P2 are more obvious compared with P1. Besides, the drag coefficient of P2 increases with β increasing. In addition, we define drag force ratio and heat transfer enhancement ratio to compare the sensitivity of particles to the changes of Re and/or Da when two particles coexist and when one particle exists alone. The results indicate the heat transfer efficiency of P1 is more sensitive to changes in Da and Re compared with a single porous particle. [Display omitted] • Lattice Boltzmann method is applied to solve the governing equations. • The leading particle has a shading effect on the trailing particle. • The two porous particles suppress each other's heat transfer efficiency. • The heat transfer of leading particle is more sensitive to Reynolds number. [ABSTRACT FROM AUTHOR]

Comprehensive exploration on the pneumatic feeding characteristics of a fluidized bed can deepen the understanding of biomass pyrolysis. An Euler-Euler model coupled with KTGF is used to simulate the pneumatic feeding process of a two-dimensional cold-flow fluidized bed. The pneumatic feeding mechanism of fluidized bed is analyzed from three aspects: feed gas, feed biomass particles and pneumatic feeding. The feed gas exerts a radial drag force on the quartz sand particles, and merges with the fluidizing gas to promote local fluidization and reduce solid hold-up, which provides feeding space for biomass particles to enter. The radial collision between feed particles and bed materials promotes the diffusion and mixing of particles. And the interaction between feed gas and feed particles promotes them to enter the bed deeper. A dynamic model of pneumatic feeding into the fluidized bed reactor is established, including particle interaction, diffusion, mixing and fluidization together. [Display omitted] • Pneumatic feeding process of cold-flow fluidized bed is numerically investigated. • Feeding mechanism is analyzed from feed gas, feed particles and pneumatic feeding. • Feed gas promotes fluidization and reduces solid hold-up to provide feeding space. • The particle collision promotes the diffusion and mixing of particles. • A dynamic model is developed to guide the pneumatic feeding of fluidized bed. [ABSTRACT FROM AUTHOR]

Inhomogeneous structures have significant impact on the drag. In this work, direct numerical simulations of flows past fluidized spheres are performed to investigate the effect of inhomogeneities on the drag at low Reynolds numbers. The inhomogeneities are quantified using various sub-grid quantities including a newly defined quantity named the solid drift flux, which is a measure of the correlation between the gas volume fraction and the particle phase velocity. Following the methodology of Rubinstein et al. (2017), a new drag model that depends simultaneously on the solid drift flux and the scalar variance of solid volume fraction is then developed. Given that these two sub-grid quantities are readily available in Eulerian-Lagrangian (EL) simulations, the developed model can be directly used in EL simulations without any additional closures for sub-grid quantities. An a priori analysis demonstrates that this model achieves satisfactory performance in predicting the drag in inhomogeneous structures. [Display omitted] • A new sub-grid quantity is proposed to measure the extent of inhomogeneities. • A new drag model considering inhomogeneities at microscales is proposed. • Comparison between the new model and available models is made based on DNS data. • The new drag model is able to give accurate predictions at different filter sizes. [ABSTRACT FROM AUTHOR]

Inter-particle and inter-phase interactions of gas-solid flows dominate macro-scale bed hydrodynamics in fluidised bed systems. In this work, typical fluidisation behaviours are presented. The effects of different drag models (i.e., Di Felice drag model, Gidaspow drag model) and collision models (i.e., hard-sphere model, soft-sphere model) on gas-solid behaviours in a bubbling fluidised bed are comprehensively compared. Besides, the influence of critical operating conditions (i.e., superficial gas velocity) is discussed. The simulation results show that Di Felice drag model shows better agreement with the experimental data than the Gidaspow drag model. Both the hard-sphere model and soft-sphere model can well predict particle velocity profiles. Larger superficial gas velocity and hard-sphere model respectively cause more vigorous inter-phase momentum exchange and more frequent collision events, indicating the more intense bubble evolution and the resulting fluctuations of void fraction. The rotational velocity obtained from the soft-sphere simulation is larger than that from the hard-sphere one, but the rotational velocity fluctuation is much weaker. [Display omitted] • Different drag and collision models are evaluated for CFD-DEM modelling of a BFB. • Hard-sphere and soft-sphere models generate similar particle velocity profiles. • Periodic fluctuations predicted by hard-sphere and soft-sphere models are different. • Hard-sphere model predicts stronger void fraction fluctuations. [ABSTRACT FROM AUTHOR]

In unresolved flow CFD-DEM simulations, the porosity values for each CFD cell are determined using a coarse-graining algorithm. While this approach enables coupled simulations of representative numbers of particles, the influence of the porosity local to the particles on the fluid-particle interaction force is not captured. This contribution considers a two-grid coarse-graining method that determines a local porosity for each particle using a radical Voronoi tessellation of the system. A relatively fine, regular point cloud is used to map these local porosity data to the CFD cells. The method is evaluated using two different cases considering both disperse and tightly packed particles. The data show that the method conserves porosity data, is reasonably grid-independent and can generate a relatively smooth porosity field. The new method can more accurately predict the fluid-particle interactive force for polydisperse particle system than alternative methods that have been implemented in unresolved CFD-DEM codes. [Display omitted] • A two-grid coarse-graining method by the radical Voronoi tessellation is proposed. • A regular point cloud is used to map the local porosity of particle to CFD cells. • Validation cases with both disperse and tightly packed particles are used. • The drag force for polydisperse particle system is accurately predicted. [ABSTRACT FROM AUTHOR]

Eulerian–Eulerian and Eulerian-Lagrangian numerical approaches are both widely used to investigate hydrodynamic behavior in dense gas-solid fluidized bed reactors, yet there has been a lack of comparative investigations involving the two. Therefore, the present work compares the numerical performance of a two-fluid model (TFM) and a dense discrete phase model (DDPM) in describing the hydrodynamic behavior of a pilot-scale bubbling bed reactor. The effects of several different parameters – drag force, grid size, fluid time-step, time-averaging interval, particle-wall specularity coefficient, particle-particle restitution coefficient, particle-wall reflection coefficient, and numbers of parcels (the latter two parameters only for the DDPM) – are investigated and compared for the two approaches using two-dimensional (2D) simulations. The numerical results for both models indicate that sub-grid drag correction based on the energy minimization and multiscale (EMMS) theory is the most essential modeling parameter to account for the multiscale structures (i.e., bubbles and void spaces) and to resolve the axial and radial solid distributions. Both the TFM and DDPM, coupled with the EMMS/bubbling drag, predict similar hydrodynamics behavior; however, the better accuracy in terms of axial and radial solids concentration profiles is achieved from the TFM approach. Further, our grid size analysis results indicate that the DDPM generates a better grid-independent solution than the TFM. This important advantage of the DDPM over TFM makes it a suitable candidate for large-scale industrial applications by employing it on much coarser grids. Meanwhile, the results from the time-step, time-averaging interval, specularity coefficient, restitution coefficient, reflection coefficient, and numbers of parcels represent a minor effect on the overall hydrodynamics behavior of the pilot-scale bubbling bed reactor. [Display omitted] • Hydrodynamics of a 2D bubbling bed was investigated with the TFM and DDPM. • Sensitivity of some key modeling parameters and sub-models was conducted. • Results in terms of numerical accuracy and computational effort were compared. • Both models provide good results with the proper selection of a drag model. • TFM provides better results while the DDPM gives a good grid-independent solution. [ABSTRACT FROM AUTHOR]

The fast advancement of existing and new functional material systems, where particulate morphology differs from traditional systems (e.g. fibers, flakes,), demands technical know-how on the processing of non-spherical particles in liquid media. There are few to no technical relevant tools available for the prediction of such particulate systems, specifically when particle-particle interactions and particle orientation are relevant, making development of such processes time consuming and expensive. Therefore, a tool is needed to support process design and further understand of non-spherical systems. On this work, a novel approach for the calculation of drag forces and drag induced torques for non-spherical particles in the context of CFD-DEM coupling is presented. The approach is inspired by Stokesian Dynamics for the computation of drag forces and torques when using the multi-sphere method for the representation of non-spherical particles. Unlabelled Image • Drag model for non-spherical particles is implemented within a CFD-DEM coupling framework using a multisphere representation • Model is validated against analytical solutions and compared to existing non-spherical drag laws • Model used for the analysis of particle orientation in a periodic rectangular channel [ABSTRACT FROM AUTHOR]

The supercritical water gasification reactor provides a green and efficient method for the utilization of organic resources such as coal and biomass. It is important to note that collision-induced particle rotation in the reactor will affect the flow and heat transfer characteristics between the particles and the fluid. At present, there is a lacking consideration of particle rotation in the supercritical water environment. The purpose of this paper is to investigate the effects of dimensionless rotation rate (Ω ∗) and particle Reynolds number (Re p) on drag coefficient (Cd), lift coefficient (Cl) and average Nusselt number (Nu) for the single particle in a supercritical water crossflow under two rotation modes, with rotation axes parallel and perpendicular to the jet direction. The flow field, temperature field, boundary layer, and surface pressure coefficient (Cp) were analyzed to interpret the variation of the particle dimensionless coefficients (Cd , Cl and Nu). It was found that the value of ∣ Cp ∣ on the particle surface rose at different locations for the two rotation modes, leading to an increase in the pressure drag and dominating the total drag force. However, the two rotation modes produced different deviating effects on the average Nusselt number. Ultimately, new correlation formulas of Cd , Cl and Nu for a rotating spherical particle in a supercritical water environment were proposed based on the results of numerical simulations, with a maximum deviation of 8.52%. [Display omitted] • The dimensionless coefficients for two rotational modes in SCW are investigated. • The pressure, friction and heat transfer between the particle surface and the surrounding flow field are analyzed. • The fitting formulas for Cd , Cl and Nu of rotating spheres in SCW are established with high accuracy. [ABSTRACT FROM AUTHOR]

A novel sub-grid drag force model is proposed for coarse-grid Euler–Euler simulation of gas–solid fluidized beds. Starting from a transport equation for the drift velocity, an equilibrium condition is used as a basis to derive a new algebraic drift velocity model. The sub-grid correlations that show up are closed by a large-eddy PDF approach inspired from LES of turbulent reacting flows. The new analytical model only depends on the resolved slip velocity and on a few sub-grid moments of the solid volume fraction. Then, a conditional averaging procedure shows that the new model can be properly captured by a simple functional expression that only requires a closure for the sub-grid variance of the solid volume fraction. A priori validation studies show that the drift velocity is predicted with high accuracy ( R 2 > 0. 90) for a large range of filter widths and for both Geldart A and Geldart B particles. [Display omitted] • Sub-grid drag modeling is needed for large-scale simulation of fluidized beds. • A theoretical drift velocity model is derived from a transport equation. • Sub-grid moments of the solid volume fraction are closed by a large-eddy PDF approach. • A scalar-variance based functional model is proposed and validated for Geldart A and B particles. [ABSTRACT FROM AUTHOR]

The particle drag force coefficient is a critical variable in modeling multiphase energy systems. Even though various empirical drag models with limited conditions have been published before, developing a general drag model is still an important topic. Existing analytical and modeling techniques of particle drag are incapable of supporting the application's complexity due to their limitations to very specific conditions. This paper proposes the Drag Coefficient Correlation-aided Deep Neural Network (DCC-DNN) architecture to predict the particle drag force coefficient from various single-particle experimental data. Beyond sphericity and Reynolds number, the proposed approach includes an expanded set of features supported by the literature. Simultaneously, model regularization and meta-learning help train a generalized and more reliable drag model, despite the limited data available and the variance exhibited in individual single-particle studies. The presented model applies to spherical and non-spherical particles, providing much-needed generality and reliability for industrial applications. [Display omitted] • Modeling Drag on Non-Spherical Particles Using DNN Models. • The model was trained using over 3000 experimental data points. • DNN aided by correlations using Stack generalization and Mixture of Expert (MoE). • DNN performance supersedes all the previous drag correlations. • Advanced shape features such as lengthwise and crosswise sphericity are considered. [ABSTRACT FROM AUTHOR]

This paper presents a computational fluid dynamics (CFD) study of the hydrodynamic force exerted on a prolate hemispheroidal particle (as a model geometry for debris formed during glass cutting) attached to a planar solid surface under linear shear flow. The three-dimensional conservation equations for mass and momentum are solved using a finite-volume scheme on a polyhedral mesh to compute the steady flow field around the particle and determine the hydrodynamic force on the particle as a function of particle aspect ratio (ε), pitch angle (θ p) with respect to the surface, and orientation angle (θ f) with respect to the flow direction. The computational results are used to develop a correlation for the drag coefficient (C D) in terms of more general shape descriptors that can be used for particles of irregular shape (i.e. , with no symmetry)– namely, lateral view factor (ψ l), particle separation (ψ s), and dimensionless hydraulic radius (ψ h). Computations are also performed for several particles with irregular shapes (resembling glass debris) and the CFD results for drag coefficient are compared to predictions of the empirical correlation. The drag coefficient correlation resulting from this study will be useful for estimating the hydrodynamic drag force exerted by the flow of cleaning fluids on irregularly-shaped particles adhering to planar solid surfaces. [ABSTRACT FROM AUTHOR]

Evaluating unconsolidated reservoirs' internal stability concerning fine migration is essential for the commercial development of natural gas hydrate resources. In this pursuit, we use our newly developed visualized sand production cell and validated CFD-DEM model to study the fines migration dynamics in unconsolidated reservoirs. Our approach leveraged the novel Analysis Software for the Internal Stability of Granular Soils (ASISGS), equipped with three distinct criteria. Experimental observations revealed reservoirs with smaller fine particles experience intensified sand production, characterized by extended production durations and a heightened presence of fine particles in the produced sand. The fine particles move faster than the coarse ones. The 'coarse matrix with floating fines' is a premise for fines migration. The flow channel severely clogged by fine particles may reopen, leading to erosive bursts. Kezdi law and the Kenney and Lau criterion in ASISGS software successfully assessed reservoirs' internal stability, consistent with our experimental results. However, the Sherard criterion sometimes overestimated the reservoir's internal stability. Rather than a binary distinction, our research posits a continuum between internally stable and unstable reservoirs. From a CFD-DEM perspective, we discerned two predominant failure modes leading to sand production: erosion of fines and destabilization of the primary sand arch subsequently triggering a sand skeleton reorganization. The smaller the fine particle size, the slower the coordination number increase, the lower the coordination number the platform reach, and the more significant the fine particle migration. With the hydrodynamic drag force exerted by the fluid, fine particles move faster and farther than coarse particles. The formation process of the sand arch includes initial, migration, and equilibrium stages. Overall, this study offers valuable insights into fines migration and its impact on sand production, providing a foundation for effective sand management in natural gas hydrate reservoirs. [Display omitted] • Use new software, ASISGS, to assess natural gas hydrate reservoir internal stability. • Verify ASISGS software by experimental results. • The CFD-DEM model shows the migration of the fine particles on a microscopic scale. • The formation of the sand arch includes initial, migration, and equilibrium stages. [ABSTRACT FROM AUTHOR]

The databases used to construct traditional mesoscale drag models is usually obtained from fine-grid simulation results in the full-periodic domains, ignoring the function of the wall boundary. In actual fluidized bed reactors, the presence of wall boundary can significantly affect the heterogeneous structures in near-wall areas, thereby affecting the drag force. Therefore, this work aims to further enhance the performance of the prediction results of existing filtered drag model by introducing the influence of the wall boundary. Based on the mesoscale drag force model published in previous literature, a correction coefficient considering the influence of the distance from the grid to the wall boundary is proposed. The applicability of the new corrected model is further enhanced by introducing the influence of solid volume fractions and slip velocities. Simple posteriori validations are systematically conducted in various common fluidized beds including the bubbling bed, the turbulent bed, and the fast bed to assess the predictive capability of the newly proposed correction drag model. [Display omitted] • The wall boundary affects the inhomogeneous structure and the drag force in near-wall regions. • The effect of the wall boundary is introduced to the existing filtered drag model. • Posteriori validations are conducted to assess the newly corrected drag model. [ABSTRACT FROM AUTHOR]

The paper assesses the behavior of cohesive Geldart C-type particles, when fluidized by air with the aid of vibration. Together with their poor flowability and irregular hopper discharge, bubbling fluidization is very difficult to achieve due to the possible particle agglomeration and gas channeling. When trying to fluidize cohesive particles, the gas drag force cannot break the inter-particle bonds. Despite all these handling and operation problems, ultrafine particles of micron- or nanosize are increasingly applied in industrial processes. To disrupt the stable gas channels and cracks, a mechanical vibration is one of the easier and preferred methods to improve the fluidity of the cohesive particles. In the present study, several 2 to 40 μm particles were used. A comparison with Geldart A-type particles was also made. Experimental results were used to validate a more fundamental approach based upon the balance of forces acting on the particles. This resulted in a new delineation of the Geldart C/A boundary where the critical transition particle size for particles of given absolute density, ρ p , Hamaker constant, H , and inter-particle distance, z 0 , decreases with an increasing vibration intensity, I , according to d crit 2 ρ p = 8.03 H z 0 2 1 + I g. Mechanical vibration is a non-intrusive method to improve the fluidity of the cohesive particles and a new Geldart C/A boundary was modified for an increasing vibration intensity. [Display omitted] • Assesses the behavior of cohesive Geldart C-type particles, when fluidized by air with the aid of vibration. • Despite handling and operation problems, ultrafine particles are increasingly applied in industrial processes. • Mechanical vibration is a non-intrusive method to improve the fluidity of the cohesive particles. • Several 2 to 40 μm particles were examined and compared with Geldart A-type particles. • Experimental results and a balance of forces provided a new Geldart C/A boundary for an increasing vibration intensity [ABSTRACT FROM AUTHOR]

The primary shape considered for the present numerical study is the spherical segment dissected from the spherical particle at an angle α from its vertical y -axis. The shape effect of the spherical segments on momentum and heat transfer characteristics are presented in terms of shape factor (ψ) spanning over the range of 0.424 (α = 300) ≤ ψ ≤ 0.996 (α = 1500) for Reynolds number, 1 ≤ Re ≤ 150. The results of drag, heat transfer coefficient, and streamlines have been compared with the closest shapes of spherical segment, i.e., cone (0.324 ≤ ψ ≤ 0.658) and short cylinder (0.541 ≤ ψ ≤ 0.872) to identify the role of the particle shape. The range of shapes has been correlated for drag and average Nusselt number as a function of Re , shape factor, ψ and particle longest chord length or base diameter to height ratio (1 ≤ d c / h ≤ 7.463). [Display omitted] • Order of C D at low Re , same base area: cone < spherical segment < short cylinder. • Particle shape modifies wake size and critical Reynolds for flow separation. • C D and Nu of short cylinder veer off from other shapes reasonably. [ABSTRACT FROM AUTHOR]

The accurate prediction of particle tracking using computational fluid dynamics is crucial for industrial processes. This study enhances the Euler-Lagrangian particle-tracking method by incorporating a point-wise particle (PWP) correction. The goal is to improve the prediction of the erosion characteristics of submerged jets by employing appropriate mesh sizes. Through mesh refinement, the predicted erosion-related parameters gradually converge to the experimental data, even in cases where the fluid field is independent of the mesh size variations. Mesh size has a more pronounced impact on smaller particles due to their lower inertia. The PWP correction primarily affects the drag force on particles near the wall, where spatial differences in fluid velocity and particle rebound timing are significant. Experimental results validate the effectiveness of the PWP correction in enhancing the accuracy of particle tracking predictions, particularly for larger particles. [Display omitted] • Mesh refinement study ensures the convergence and accuracy of particle tracking. • Tracking is based on the correction for PWP in particle tracking prediction. • Correction for PWP improves the accuracy of particle tracking prediction. [ABSTRACT FROM AUTHOR]

Highly efficient PM 2.5 filtration has been obtained experimentally using a fluidized bed. In this work, a CFD-DEM simulation was conducted to investigate the effects of operating conditions such as the superficial velocity, fluidization state, and PM size. These effects were assessed in terms of the capture ratio and the forces acting on the PM. A high collection efficiency is reproduced at PM diameters of less than 20 μm and superficial velocities of 0.3–0.6 m/s. Most of the PM is captured by adhesion in the bottom two to six layers of bed particles, where the void fraction is low. The adhesion force is the dominant force, and the drag force is negligible even at a superficial velocity of 0.6 m/s. After the PM is captured, it moves with the bed particles in this system. The adhesion force is still dominant for a 30 μm PM at 0.4 m/s. The capture ratio is 87.5%. However, the PM–bed particle collision velocity increases with increasing superficial velocity, and the repulsive force becomes large. The capture ratio decreases dramatically with increasing superficial velocity. The repulsive force becomes dominant for PM diameters above 40 μm, and most of the PM cannot be filtered. Unlabelled Image • CFD-DEM numerical simulation of PM filtration using a fluidized bed was conducted. • Highly efficient fine PM filtration was reproduced based on the van der Waals force. • Most PM is captured in bottom bed layer, where bed particles are nearly close-packed. • PM (≤20 μm)–bed particle adhesion force is dominant and, drag force is negligible. • Captured PM is stirred by fluidization but is retained on bed particles. [ABSTRACT FROM AUTHOR]

In this work, the drag force correlation specific for fixed random arrays of elliptical cylinders is formulated under Re = 0.1–100 using Lattice Boltzmann method (LBM) and discrete element method (DEM). The LBM-DEM model is validated by comparing with experimental and simulation data. To achieve this, first, a new simple drag force correlation format is developed, containing modified permeability (K′) and inertial terms (α, λ). Then the effects of elliptical cylinder shape (Ar) on K′ , α , and λ for random arrays of elliptical cylinders are studied, where Ar ranges from 0.3 to 1.0; and by curve-fitting the simulation results, the correlations of K′ , α and λ are formulated as a function of Ar. One can obtain the reliable drag force correlation between the fluid and elliptical cylinders in a fixed random array via specifying K′ , α and λ for a given Ar and then plugging them in the proposed format. Unlabelled Image • A LBM-DEM method is used to study fluid flow through arrays of elliptical cylinders; • A drag force format, containing permeability and inertial terms, is developed; • Drag forces on individual elliptical cylinders show a probability distribution; • Correlations are proposed to estimate the mean drag force on elliptical cylinders. [ABSTRACT FROM AUTHOR]

The separation of coarse particles by flotation can be maximized by the support of fluidized bed hydrodynamics. Here, we investigated the effect of particle size and shape on the liquid-solid fluidization in a HydroFloat cell that was developed for the special separation process using CFD results and experimental data. Specifically, a 3D CFD model was developed to study the liquid and aspherical quartz particle flow behaviors in a fluidized bed in the cell. The Eulerian–Eulerian formulation with the RNG k-ε turbulence model was applied for the liquid phase, while the kinetic theory of granular flow was utilized for the particle phase. The Gidaspow with Haider and Levenspiel equations were used for the drag force coupling between the liquid and the aspherical particles. The CFD results agreed with the experimental data for the bed voidage and pressure drop. The CFD model was further applied to investigate the effect of particle size (d S) and particle shape factor (ψ) on the bed expansion, pressure drop, and voidage of the fluidization for Re (particle Reynolds number) < 11.6. The Richardson-Zaki equation was modified to predict the voidage, within 12% of relative errors. The prediction was further improved by our semi-empirical correlation that reduced the errors to 8%. The particle size and shape were also found to significantly affect the time-averaged radial distribution of the axial velocity and volume fraction of the particles, granular temperature, dissipation rate, and viscosity of turbulence. The outcomes of this paper are useful for optimizing the operation of the HydroFloat cell. Unlabelled Image • Effect of particle size and sphericity on liquid-solid fluidization. • Low bed expansion and pressure drop for large particle size and shape. • Estimated voidage agrees with the modified Richardson-Zaki model. • Low sphericity of particles increases energy transfer efficiency. [ABSTRACT FROM AUTHOR]

The open source code MFIX is used to perform CFD-DEM and TFM simulations based on the small scale challenge problem 1 fluidized bed set up. The basic flow features such as the core-annulus structure and slugging dynamics are well predicted by both modeling approaches. Similarly the first four statistical moments of the particle velocity distributions from HsPIV measurements are equally reproduced qualitatively by the models. The predicted mean pressure drop is independent of the drag correlation used in both modeling frameworks but the CFD-DEM model gives predictions closer to the experimental values. Predicted fluctuating quantities such as rms and granular temperature show sensitivity to the drag model used. The TFM demonstrates greater accuracy over the CFD-DEM in prediction of the particle granular temperature while the opposite is true for the bubble granular temperature. CFD-DEM simulations on average take twice the time required to perform a TFM simulation. Unlabelled Image • CFD-DEM and TFM modeling of small scale challenge problem. • Spectral analysis of pressure and particle velocity fluctuations. • Statistical analysis of pressure and particle velocity data. • Comparison of particle and bubble granular temperatures. [ABSTRACT FROM AUTHOR]

High aspect ratio ellipsoidal particle suspensions exhibit preferential orientation under the action of external forces and in the presence of walls. The preferential orientation of the particles has a large effect on the drag force experienced by the suspension. In this paper particle resolved simulations are conducted on ellipsoidal particles of aspect ratio 10 and 2.5 in the Reynolds number range 10 ≤ Re ≤ 200 and solid fractions 0.10 ≤ φ ≤ 0.30. An orientational order parameter −2.0 ≤ S ≤ 1 is used to define the preferential orientation of the suspension. It is shown that in spite of up to 400% variation in mean drag force with S , a simple linear relationship between S = −2 and 1 can describe the variation of drag force. This is a significant finding which establishes that only two data points at S = −2 and 1 are needed to define mean drag at any preferential orientation exhibited by the suspension. It is also shown that the inclination dependent mean drag is quite independent of S at low Reynolds number and solid fraction but shows increasing dependence at higher values. Unlabelled Image • Particle-resolved simulations are performed for prolate ellipsoid suspensions. • Orientational order parameter (S) is used to quantify the orientation preference. • Mean drag shows linear dependence on orientational parameter S. • Inclination dependent drag force is independent of S at low solid fraction (φ). • At larger φ , drag increases with S at identical inclination angles. [ABSTRACT FROM AUTHOR]

Understanding the aerodynamic forces on particles resting on a surface is important for studies of surface contamination, non-contact sampling, and environmental and health assessments. Though the aerodynamic forces acting on a spherical particle are well studied, in many real-world applications, the particles are non-spherical, and there are currently no established relations for forces on non-spherical particles resting on a surface. We developed new relations for the aerodynamic forces on prolate-spheroidal particles attached to a surface in a linear shear flow using direct numerical simulations. The reduced-order model predicts drag, lift, and torque coefficients as a function of the particle aspect ratio, flow incidence angle, and Reynolds number. The predictive model agrees with the direct numerical simulations (DNS) results for the drag and lift coefficients within 0.3% and 3%, respectively. Unlabelled Image • Direct numerical simulation for linear shear flow over prolate spheroids attached to a surface. • Aerodynamic forces are predicted as function of orientation, aspect ratio, and Reynolds number. • Drag force is predicted within 0.3% of DNS. • Lift force is predicted within 4% of DNS. [ABSTRACT FROM AUTHOR]

The fundamental problem encountered in the bubbling fluidized bed reactors is the presence of multiscale structures which cannot be resolved by the conventional drag models. In this study, a novel hybrid Eulerian-Lagrangian dense discrete phase model (DDPM) based on energy minimization and multiscale (EMMS) drag is proposed for the first time to analyze the hydrodynamics of bubbling fluidized bed reactors with Geldart A, A/B, and B particles. By comprehensive and comparative investigations of a number of key modeling parameters (grid size, drag force, particle number per parcel, turbulence, and particle-particle restitution coefficients), our proposed DDPM-EMMS model stands out of the currently-available counterparts in terms of improved grid-independency, multiscale structures resolvability with coarser grids, better parcel-independency, and better performance with laminar treatment against turbulence. Unlabelled Image • Hydrodynamics of bubbling bed reactors with DDPM-EMMS approach was investigated. • Effects of key modeling parameters for DDPM-EMMS approach were investigated. • For Geldart A and A/B particles, DDPM with EMMS drag can predict better results. • For Geldart B particle, DDPM with Gidaspow drag can predict reasonable results. [ABSTRACT FROM AUTHOR]

A detailed study of parameters influencing the transition from bubbling to turbulent fluidization was done. The transition velocity U c was determined by pressure fluctuation analysis for different size fractions of sand and ilmenite particles (Geldart's group B). Four different plants (laboratory and pilot scale) were used having diameters ranging from 0.05 m to 0.4 m. The static bed height was varied, resulting in aspect ratios (static bed height/bed diameter) from 1 to 4. The results of U c show a clear dependency of aspect ratio, bed diameter, temperature and particle size. The diameter of the bed was found to influence the transition velocity especially in small fluidized beds. The static bed height has a significant influence on the transition velocity which has to be considered in scale-up. As a further parameter, the temperature influence was investigated up to 800 °C. No correlation in literature was found to predict satisfactorily the influences of the parameters investigated. Unlabelled Image • Transition velocity U c from bubbling to turbulent fluidization was investigated. • Particle properties, bed diameter, static bed height and temperature were analyzed. • Temperature influence was found to rely on the drag force acting on the particles. • No correlation available in literature considering all parameters investigated. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation of a disk-shaped rotor rotating inside a granular medium using the discrete element method, and the torque, quantitatively characterizing the resultant of drag forces on the rotor from surrounding particles, is mainly explored. The existence of a dumbbell-shaped region induced by the rotating rotor may essentially give rise to the steady state independent of initial loading conditions, in which the pressure difference between the upper and lower surfaces of the disk disappears and the torque always tends to a stationary value. Furthermore, the rotation of the rotor induces an anisotropic structure with the formation of arches that screen the vertical pressure, leading to the occurrence of the low-pressure region above the rotor. Finally, a scaling law of the torque with the depth is proposed, in which the rotation speed of the rotor as an affecting factor is also taken into account. Unlabelled Image • The drag force experienced by a disk-shaped rotor is studied based on DEM. • The steady state is independent of the initial loading conditions. • The rotation of the rotor induces a dumbbell-shaped activated region. • The formation of arch structure screens the vertical pressure. • The scaling law of the torque with the depth and the rotation speed is proposed. [ABSTRACT FROM AUTHOR]

The gas-solids flow in high-density downers with FCC particles was simulated by Computational Particle Fluid Dynamics (CPFD) approach. A drag model was proposed based on the equivalent diameter of cluster with the analysis of force balance on particle cluster. A global sensitivity analysis method was used to analyze the influencing factors of cluster size. The drag model was incorporated into the three-dimensional (3D) CPFD approach to simulate the gas-solids flow in two different downers operating at various conditions. 3D CPFD simulation provided detailed trajectories and distributions of solids. Good agreements of the predicted solids holdup and velocity with experimental data were achieved at both low and high-density conditions, which verified the rationality and applicability of the present drag model considering the characteristics of particle cluster in the downer. Finally, the flow and clustering behavior in the high-density downer were adequately analyzed and compared with that in low-density downer. Unlabelled Image • High-density downer is a novel reactor that is potential for processing heavy oil. • CPFD simulation was performed for the high-density downer. • A cluster-based drag model was proposed with analysis of force balance on cluster. • The cluster-based drag model was capable of capturing particles flow behaviors. • Gas-solids flow behaviors were compared between high and low-density downer. [ABSTRACT FROM AUTHOR]

To account for the sub-grid heterogeneity of bubbling gas-solid flows in the multi-phase particle-in-cell (MP-PIC) method, a bubble-based EMMS/DP drag model is proposed in this work by taking into account the particle/parcel position information. The local, inter-parcel porosity is calculated by using the method of smoothed particle hydrodynamics (SPH), while the intra-parcel porosity is closed by using the Energy Minimization Multi-scale (EMMS) model. The local velocities of gas phase and different solid parcels are determined by using the constraint of pressure drop balance between phases as in the EMMS/bubbling model. The drag force acting on each parcel is then determined with the sub-grid information of velocities and porosities. Two cases of bubbling fluidized bed are simulated to validate this drag model. And the results show good agreement with experimental data. Unlabelled Image • A bubble-based EMMS/DP drag force model is proposed for MP-PIC method. • The model accounts for the particle/parcel position and velocity information. • The model is compatible with Eulerian-Lagrangian method. • The model gives much higher accuracy in MP-PIC simulations of bubbling bed. • The effect of the number particles per parcel and grid resolution has been analyzed. [ABSTRACT FROM AUTHOR]

The effect of external acoustic fields on hydrodynamic behavior of cohesive micron-sized particles in a pseudo-2D fluidized bed is studied using CFD-DEM simulations. The forces acting on a particle consist of the contact force and cohesive force between particles, the drag force by the surrounding fluid and the sound force by an acoustic field. A wide range of sound pressure levels and sound frequencies are investigated in terms of their effects on the pressure drop, bed expansion, distribution of particle velocity and concentration, as well as the sizes of bubbles and agglomerates. Comparing to the system without acoustic force, the application of acoustic field is found to induce the breakup of the formed agglomerates, and ultimately lead to a stable bubbling fluidization regime. A useful range of frequencies between 80 Hz to 100 Hz is found with a pressure level of 120 dB, resulting in most remarkable improvement of the process performance. Unlabelled Image • CFD-DEM simulations of fluidization of cohesive particles with acoustic fields. • The sound effects on pressure drop, bed expansion, solids motion, bubble and agglomerate size. • A useful range of sound frequencies and sound pressure level is proposed. [ABSTRACT FROM AUTHOR]

An expression of the filtered Eulerian drag force is proposed based on the second order Taylor polynomial approximation of a microscopic drag coefficient. Theoretical computations of the expression at low particle Reynolds numbers show that four sub-grid quantities, the gas drift velocity, the solid drift velocity, the scalar variance of solid volume fraction and a third-order moment, are significant for an accurate estimation of the filtered drag force. Various drag models with different combinations of the four sub-grid quantities are proposed and their coefficients are optimized based on fine-grid two fluid model results. The gas drift velocity is demonstrated to be the most important marker in predicting the filtered drag force. The model with the solid drift velocity and the scalar variance of the solid volume fraction is found to be promising in computational fluid dynamic-discrete element model simulations due to the ready availability of the two sub-grid quantities. Unlabelled Image • Four sub-grid quantities are demonstrated to significantly affect filtered drag force. • Gas drift velocity is the most important marker in predicting filtered drag force. • Models with different combinations of the four sub-grid quantities are established. [ABSTRACT FROM AUTHOR]

The influence of particle concentration on the drag force of a particle deserves attention when using the Lagrangian particle tracking methods for the prediction of industrial type gas-solid flows. The Lagrangian approach is best suited to applications where the solids volume fraction is low and the effect of particle concentration can be ignored. The paper successfully predicted the available experimental findings on the effects of particle arrangements on drag force. These successful predictions lead to the development of a new coefficient of drag for particles in cluster. Then a combined experimental and numerical study of free-falling particles was carried out in this study to investigate the behaviour of particles in cluster. The new coefficient of drag proposed in this study was used in the numerical simulations. The study highlighted the increase in terminal velocities of particles within cluster streams. The numerical simulations, obtained with the newly proposed coefficient of drag, showed improved results for the average size particles used. The improvements obtained for larger particle size particles were not as impressive. Unlabelled Image • The paper successfully predicted the effects of particle arrangements on drag force. • A new drag coefficient for particles in cluster is proposed in this paper. • The use of the proposed drag coefficient improved results for average size particle. • This work highlighted the increase in terminal velocity of particles within cluster. [ABSTRACT FROM AUTHOR]

Detailed micromechanical analysis of an individual bubble injected into a three-dimensional incipiently fluidized bed is carried out by means of a coupled CFD-DEM approach. The distribution of interphase drag force vectors is consistent with the gas flow pattern based on the potential flow theory. The non-uniformity of drag force caused by bubbles is quantitatively analyzed. Moreover, a bubble-induced inhomogeneous coefficient is presented to assess the ensemble bubble impact. The effects of particle diameter and gas injection velocity are evaluated. The results reveal that the bubble negative effect on interphase drag force is strengthened by increasing the particle diameter and gas injection velocity. Unlabelled Image • Micromechanical analysis of an isolated bubble in a fluidized bed is studied. • The change of interphase drag caused by bubble force is evaluated. • Model prediction agrees well with experimental data. • Sensitivity of drag force around bubble to operating parameters is examined. [ABSTRACT FROM AUTHOR]

To model drag the current state-of-the-art is to use isolated non-spherical particle drag correlations modified by a solid fraction correlation that is based on experimental or simulation results of spherical particle suspensions. It is shown that this practice can lead to substantial inaccuracies when the particle geometry deviates significantly from a spherical geometry. In this paper particle resolved simulations (PRS) are conducted for ellipsoids of aspect ratio 5 (AR5) and 10 (AR10) in random suspensions with no preferential orientation. Simulations are performed for a Reynolds number Re = 10 to 200, and solid fraction φ = 0.1 to 0.3 and 0.1 to 0.2 for AR5 and AR10 suspensions, respectively. Combined with PRS data from past studies for spherical particle suspensions and ellipsoids with AR2.5, a drag correlation is developed for the mean drag force in suspension as a function of Re , φ , aspect ratio, and inclination angle θ. Unlabelled Image • Particle-resolved simulations are performed for suspensions of ellipsoids. • Drag force depends on solid fraction, Reynolds number, particle inclination and geometry. • Significant deviations are observed using drag correlations in literature. • New drag correlation accounts for particle geometry in suspension. • Drag correlation has mean deviation of 5% over a large range of conditions. [ABSTRACT FROM AUTHOR]

Non-Newtonian fluid flows through packed beds are common in many industries. Our understanding of this flow system is very limited, and the correlations for describing the fluid-particle interaction are not fully established. To overcome these problems, this paper presents a comprehensive study of this system on a sub-particle scale, with a special reference to the interaction between fluid rheology and bed properties. This is done by conducting about five hundred Lattice Boltzmann simulations under different conditions. The fluid rheology is represented by the power-law model to consider the shear-thinning, shear thickening and Newtonian behaviors of fluids. The simulation condition covers a wide range of bed porosity, particle size distribution and Reynolds number (Re). The results show that the effect of fluid rheology on the fluid behavior is strong. This effect varies significantly with bed porosity which is a function of particle size distribution. The interplay between fluid rheology and bed properties is however not strong in determining the distributions of particle-fluid interaction force. Based on the simulation data, a new drag correlation is established and validated against the experimental data in the literature. This correlation is more accurate and consistent than those reported in the past. It can estimate the mean drag forces on individual particles of different sizes, and is recommended to be used generally in the modeling of particle-fluid flows either for Newtonian fluids or for non-Newtonian fluids obeying the power-law model. Unlabelled Image • Lattice Boltzmann simulation has been conducted to study the non-Newtonian fluid flow in packed beds. • The interplay between fluid rheology and bed properties is examined under different conditions. • Particle-fluid interaction forces are quantified in terms of spatial and statistical distributions. • A new correlation is formulated to estimate generally the mean drag force. [ABSTRACT FROM AUTHOR]

Selection of process parameters is an important step in Powder-Based Additive Manufacturing (PBAM) of metals. In order to achieve an optimal parameter set, current literature is mainly focused on the understanding of powder dynamics by analysing the aerodynamic forces. In this letter, however, we show the importance of the laser induced force (radiation pressure) on the powder dynamics. Generalised Lorenz-Mie theory has been employed to accurately estimate the radiation pressure and it is shown that its magnitude is significant in comparison to various aerodynamic forces and the grains weight, hence, can significantly contribute to denudation and spatter observed in the manufacturing process. Furthermore, the importance of compressibility and rarefaction effects on the magnitude of drag and lift forces that a particle experiences is demonstrated by estimating the Ma and Kn numbers under process conditions, which directly impact the powder dynamics. Unlabelled Image • The significance of the radiation pressure on powder dynamics in AM is demonstrated. • The compressibility and rarefaction effects on the aerodynamic forces are highlighted. • Lorenz-Mie theory is adopted to accurately model the powder-laser interaction. [ABSTRACT FROM AUTHOR]