Bed Of Particles Research Articles

Particle based Large Eddy Simulation of vortex ripple dynamics using an Euler–Lagrange approach

A volume-filtered Large Eddy Simulation (LES) of oscillatory flow over a mobile rippled bed is conducted using an Euler–Lagrange approach. The modeling is done to complement the experimental work, which shows quasi-steady state ripples in a sand bed under oscillatory flow, as observed in unsteady marine flows over sedimentary beds. Simulations approximate the experimental configuration with a sinusoidal pressure gradient driven flow and a sinusoidally shaped rippled bed of particles. The LES equations, which are volume-filtered to account for the effect of the particles, are solved on an Eulerian grid, and the particles are tracked in a Lagrangian framework. A Discrete Particle Method (DPM) is used, where the particle collisions are handled by a soft-sphere model, and the liquid and solid phases are coupled through volume fraction and momentum exchange terms. Comparison of the numerical results to the experimental data show that the LES-DPM captures the mesoscale features of the system. The simulations reproduced the large scale shedding of vortices from the ripple crests observed in experiments. Likewise, the simulations exhibited quantitative agreement between the wall-normal flow statistics, and qualitative agreement in ripple shape evolution and sand particle entrainment behavior above the fluid-bed interface. The numerical data provide insight into the formation of shear layers and eddies within the flow field above and through the ripple and their influence on the particle transport and the dilation of the ripple mobile layer thickness during an oscillatory period. The resolution of flow structures within the particle bed in the LES-DPM simulations make the framework a unique tool for investigating ripple driven sediment transport and distribution of momentum over the ripple.

CFD-DEM Investigation on Pressure Drops of Heterogeneous Alternative-Layer Particle Beds for Low-Carbon Operating Blast Furnaces

Low-carbon operation technologies of the blast furnace (BF) are crucial for reducing carbon dioxide emissions from the steelmaking industry. The variation characteristic of permeability and structure in a BF lumpy zone has a critical impact on achieving low-carbon operations. Still, their influences have not been fully understood, and related studies are very limited. To solve the problem of the deteriorating permeability of blast furnaces after lowering the coke ratio, this study aims to provide insights into the pressure drop of the lumpy zone in an ironmaking BF based on computational fluid dynamics coupled with the discrete element method (CFD-DEM) model. The study systematically investigates the influence of different packing configurations on permeability using a heterogeneous alternating-layer (HAL) packed bed. After the model was validated by comparing the simulation’s results with ones calculated by the Ergun equation, it was used to investigate the effects of the number of layers, coke-mixing ratio, nut coke replacement ratio, and particle-size ratio on the structure, void fraction variation, and pressure drop of the HAL packed bed. The results reveal the effect of these factors on the permeability of the lumpy zone, providing fundamental guidance towards low-carbon operations of BFs.

Movement and velocity of a particle in an inverse fluidized bed

The movement of particles in the fluidized bed primarily determines the mixing in the bed and determines the transfer intensities that occur between the particles and the fluid. Experimental monitoring of the velocity of the marked particle was performed in an inversely fluidized bed of polypropylene, polyethylene, and polystyrene particles. The velocity of the marked particle was monitored in a two-dimensional column, where water and an aqueous solution of glycerin were used as the fluidization medium. Using the Tracker Video Analysis program (Tracker Video Analysis, Open Source Physics, 2003), the mean velocity of the marked particle was determined, as well as the distance crossed by the marked particle in the x and y directions. The influence of fluidization medium viscosity and particle density on the velocity of the marked particle was investigated. The results of experimental investigations have shown that the particle velocity distribution approximately follows the Maxwell distribution. Comparison of the measured values of the mean velocity in the inversely and conventionally fluidized bed showed a certain deviation. In this paper, a correlation for determining the mean particle velocity in an inversely fluidized bed is proposed.

Simulation of the Calendering Process of NMC‐622 Cathodes for Lithium‐Ion Batteries

Calendering is the final step in electrode production during the manufacturing of lithium‐ion batteries. It is a crucial process that significantly influences the electrodes’ mechanical and electrochemical properties and is decisive in defining their volumetric energy density and performance. Herein, a discrete element method modeling approach is proposed to predict the process parameters of the calendering process. In particular, the roll gap width is required for a given target porosity. For this purpose, a particle bed of 9 mm in length is compacted using a roll section enabling a deeper look into the compaction behavior of the microstructure. Six NMC‐622 electrodes with different thicknesses are produced and compacted to different porosities. In the experimental investigation, the roll gap width is set and measured allowing a simulative replica of the process. With the process simulation, the force propagation within the electrode can be observed on a particle level. Furthermore, nanoindentation measurements with NMC‐622 cathodes provide information on the densification behavior of cathodes and support the parameterization of the particle bed. The particle‐based simulation of the compaction process is experimentally validated using nanoindentation measurements on NMC‐622 cathodes.

Bubble-Based EMMS Drag Model for Particle Segregation Simulation with a Continuous Size Distribution

Particles in industrial fluidized beds are usually continuously distributed rather than monodisperse in size, and the separation of particles is a key factor in determining the performance of the fluidized reactor. In this paper, a bubble-based Energy Minimum Multi-Scale (EMMS) drag model was proposed to simulate polydisperse segregation in a gas–solid fluidized bed. Particle size distribution (PSD) was split into a sufficient class of characteristic particle sizes. Each size was treated as a solid phase, and the total drag force could be estimated by considering the influence of all solid phases and mesoscale structures. The EMMS drag model was then coupled with the Eulerian multi-fluid model (MFM) to simulate the segregation behavior of a polydisperse particle system. The effects of discrete particle size classes, different drag models, and gas velocities on the simulation results were also discussed under different operating conditions. The results showed that the present drag model was in better agreement with the experimental data in terms of axial solids concentration and mean particle size distribution than other models. In bubbling beds, the segregation patterns of polydisperse particles can be well predicted by this method.

Experimental Investigation on Debris Bed Quenching With Additional Non-Condensable Gas Injection

Abstract Severe accidents of light water reactors with core degradation can lead to the formation of a, so-called, debris bed inside the reactor cavity. In the scenario of depleted residual water, the bed can partially melt and interact with the concrete underneath generating noncondensable gases (NCG) at the bottom of the particle bed, which will flow through the debris bed. The impact of additional gas on the quenching process can in principle be considered in thermal-hydraulic system codes such as ATHLET; however, there is still a need for experimental validation of respective models or verification of corresponding simulation results. Therefore, especially for the model validation of COCOMO-3D, which is implemented in ATHLET, a specific extension to the existing experimental database is required. Experimental results of the quenching behavior of a monodispersed particle bed at top-flooding cooling condition with additional NCG injection, utilizing the new built-up test facility FLOAT (flooding facility with gas injection), are presented.

Ordered packing of uniform spheres via random packing protocol

The packing structure of granular materials is crucial to their performance. Uniform granular spheres always form a disordered packing when randomly fed into a container, which is considered as a natural consequence and a prototype of glass transition. This paper presents a method to design containers to promote ordered packings. In a particular container, mono-sized granular spheres can self-assemble into a single crystal without human interventions when randomly fed at a small rate, and hence achieve much higher packing density than the normally obtained random packings. The container is designed to achieve the consistency of ordered structures formed on the boundary and at the centre, so that a new particle can always be assembled into a crystal lattice node simply by gravity. Such container is generally effective for the self-assembly of uniform size spheres of different material properties (density, friction coefficients, size, etc.). Similarly designed containers can also be very effective to achieve ordered packings under vibration, which provides a method to densify packed beds of granular particles. Moreover, the finding indicates that glass transition or crystallisation could result from boundary symmetry in addition to other factors. It also suggests a way to design boundaries to promote the self-assembly of particles in general.

Numerical simulation study on mixing characteristics of binary Geldart-D particles in a pressurized fluidized bed

Understanding the mixing behaviors of different particles is significant for improving the mass and heat transfer performance of a pressurized fluidized bed. A numerical simulation study on the mixing behavior of binary Geldart-D particles in a pressurized bubbling fluidized bed is performed based on the CFD-DEM method. The mixing characteristics and bubble behavior of binary Geldart-D particles with different physical properties under elevated pressure are investigated in the current study. Increasing the fluidization gas velocity u g and operating pressure P could promote the mixing of the particles. Raising the operating pressure P would cause a smaller bubble size and large bubble quantity at the same fluidization number u g /u mg . Higher operating pressure P and fluidization number u g /u mg could create a stable and uniform distribution of jetsam in the fluidized bed. • Mixing behaviors in the pressurized fluidized bed are investigated by CFD-DEM. • Minimum fluidization velocity decrease as the increase of operating pressure. • Bubble size decreases as raising operating pressure of fluidized bed. • High operating pressure and gas velocity promote the mixing rate of particles.

Recent advances in studies of wet particle fluidization characteristics

Wet particle fluidization is commonly applied in some industries such as catalytic cracking, pharmaceutical manufacturing, mineral processing, food drying, etc. Understanding the within fluidization characteristics is important for the scale-up, design and optimization of industrial process. This article reviews the recent studies on fluidization characteristics of wet particles in fluidized beds and spouted beds. Both physical experiment and numerical simulation results are included. For physical experiments, the focus is on the development of new measurement methods and the resulting findings. For numerical simulations, the focus is especially on the development of the discrete element method (DEM) which can lead to new insights for wet particle fluidization at particle scale. Finally, challenges and needs for future research on wet particle fluidization are discussed.

Influence of cycle time distribution on coating uniformity of particles in a spray fluidized bed by using CFD-DEM simulations

Cycle Time Distribution (CTD) plays a critical role for determining uniformity of particle coating in spray fluidized beds. However, the CTD is influenced by both geometrical structure and operating conditions of fluidized bed. In this study, a spray fluidized bed of coating process is simulated by a comprehensive Computational Fluid Dynamics-Discrete Element Model (CFD-DEM). To achieve different behaviors of CTD, some modifications are designed on a pseudo-2D internally circulating fluidized bed, which traditionally composes of a high-velocity upward bed and low-velocity downward bed. These modifications include making the air distributor slope and/or laying a baffle in the downward bed. First, the CTD and evolution of particle size distribution under different bed structures are compared. The CTD directly influences the coating uniformity. By making the particles flowing along a parallel direction in the downward bed through the geometrical modifications, the CTD becomes narrower and the coating uniformity is significantly improved. Second, under the optimized bed structure, the influence of operating conditions on the coating uniformity is studied. Properly increasing the fluidization gas velocity and the fluidization gas temperature and reducing the liquid spray rate can improve the coating uniformity.

Experimental study on the pressure drop of a packed bed with reactor material particles

When a severe accident with reactor vessel failure occurs, molten core material can be released from the reactor vessel to the reactor cavity. According to a pre-flooding strategy, molten core material are released into the pre-flooded cavity and fragmentized into fine particles. Then, a particulate debris bed can be formed at the bottom of the cavity. Penetration of the coolant into the debris bed is important to ensure long term coolability of the debris bed, which is closely related to the two-phase flow pressure drop characteristics of the porous debris bed. This study analyzed the basic characteristics of non-explosive TROI (Test for Real cOrium Interaction with water) particles collected from steam explosion tests with reactor materials and then conducted single- and two-phase pressure drop experiments in the non-explosive TROI particle bed. Based on an analysis of the experimental data with existing pressure drop models, we found that the Ergun model with an effective diameter of 1 mm predicted single-phase pressure drop results most precisely and the Schmidt model with an effective diameter of 3 mm and the Schulenberg & Muller model with an effective diameter of 2 mm predicted the two-phase pressure drop results well. In addition, this paper discusses in detail the effects of the TROI particulate bed characteristics, irregularity, polydispersity and high porosity on pressure drop characteristics. Accordingly, the paper suggests a modified two-phase pressure drop model reflecting the measured porosity in the TROI bed particle.

Performance analysis of a 2D numerical model in estimating minimum fluidization velocity for fluidized beds

The minimum fluidization velocity of a fluid–solid particle fluidized bed is the primary focus of this paper. The computationally economic Eulerian Granular model has been used to analyze fluidization for both gas–solid particle and liquid-solid particle fluidized beds. The conventional approach of finding minimum fluidization velocity (umf) is either with a pressure drop across the particle bed or the change in bed height. However, these parameters are often unstable and cannot be used to generalize the degree of fluidization accurately. In this paper, the dominant factor of unstable pressure drop estimation in the 2D Two-Fluid Model (TFM) and a key non-dimensional Euler number has been investigated in determining minimum fluidization velocity for different quasi-2D fluidized beds for different bed sizes, particle sizes, and particle numbers. Averaging assumptions and limitations of these numerical models are discussed in detail for four different fluidized bed cases. A comparative study of the drag model shows little to no influence in unstable pressure drop estimation near fluidization velocity, and all drag models perform similarly. It is observed that particle-particle collision is not the dominant reason for unstable pressure drop near minimum fluidization. Instead, wall effects on the particle bed including frictional losses and wall-particle collision play a key role in unstable pressure drop calculation for the quasi-2D fluidized beds. Pressure drop characteristics alone do not suffice to obtain minimum fluidization velocity with 2D TFM using existing models. Thus, a different approach has been proposed to investigate minimum fluidization involving the Euler number, which has shown promising performance in determining minimum fluidization velocity and characterizing fluidization with 2D TFM. Results show consistency in Euler number characteristics for all different fluidized bed cases considered in this paper. This can revitalize computationally economic 2D Eulerian simulations, increase the range of possible applications, and provide guidance to the future development of computationally efficient and more accurate numerical models, and empirical correlations for minimum fluidization velocity.

Settling of heavy cylindrical particles in granular beds

The way a rigid cylindrical particle falls through a viscous Newtonian liquid into a loosely packed granular bed of smaller and lighter particles has been studied numerically. This solid-liquid flow system has been solved with the lattice-Boltzmann method combined with an immersed boundary method for explicitly imposing no-slip at the particle surfaces. We study the effect of the orientation of the cylinder (vertical and horizontal), its settling speed (the Reynolds numbers at impact is of the order of 100), and its density (relative to liquid and bed density) on the depth of penetration into the granular bed. The simulation results are particularly sensitive to the friction between particles as parameterized through friction coefficients (varied in the range 0.15 – 0.50). The results have practical relevance for particles getting immobilized – or even buried – in granular beds. More importantly, the simulation cases have been designed such as to allow for straightforward experimentation the results of which would be valuable for further numerical model development.

Gas Flow and Pressure Drop in Charge Material in Silicon Production

Gassing, outbursts of high-rate gas flows through the taphole, is a phenomenon that sometimes occurs during tapping of silicon furnaces. In addition to being an HSE challenge, this might also affect the tapping, while the warm gas might harm the equipment in the tapping area. The pressure above the metal bath, influencing the gassing, is affected by permeability, and the gas flow through the charge materials in the furnace. Pressure drop and permeability have been measured for different gas velocities through particle beds of different charge mixtures, with the raw materials and particle sizes used in industrial silicon production. The experimental results have been upscaled to conditions in industrial furnaces through modeling flow in a packed bed. The findings are compared with results from measurements of pressure drop in industrial furnaces.

Inclined-flow segregation characteristics of multi size particles in a moving granular bed

Multi-layer particle bed has an important application in the field of high temperature filtration. This paper uses the Discrete Element Method to study the flow and segregation characteristics of multi size mixed particles on inclined surfaces. The research results show that: in the process of segregation, the particles mainly carry out rolling motion; when the replacement rate of the particles reaches 60%, the degree of segregation reaches the maximum, and the optimal incline length is 600 mm. A universal quantification index for particle bed segregation and a criterion for the steady state of particle flowing are obtained. The particle size distribution close to continuous distribution is not conducive to particle segregation. The segregation effect of the largest and smallest particles in the mixed particles is better than that of the intermediate particles. This study provides a reference for the design of the segregation layered structure of the multi size particle bed.

Evolution of Melt Pool and Porosity During Laser Powder Bed Fusion of Ti6Al4V Alloy: Numerical Modelling and Experimental Validation

Laser powder bed fusion (L-PBF) is one of the most promising additive manufacturing technologies for metals. In this work, the discrete element method (DEM) was used to reproduce a powder bed of particles distributed in a random way to be as close as possible to reality. Single and multiple scan tracks simulations were performed for Ti6Al4V alloy using a commercial CFD software, FLOW-3D AM®. The output from the numerical simulations was elaborated to obtain shape and size of melt pools, morphology of scan track surfaces and porosity content. In particular, a specific model was used in order to predict air entrainment in the melt pool and, therefore, to estimate gas porosity content, as an innovative approach to predict such defects. Results from simulations were compared with experimental data from Ti6Al4V samples produced by L-PBF in terms of melt pools size and morphology, as well as density. The good agreement between calculated and experimental results indicates that simulation of L-PBF can represent a powerful tool not only for the optimization of process parameters, but also for the prediction of porosity level.

Momentum-heat-mass transfer analogy in gas-solid packed bed at elevated temperatures

The experimental values of the friction factor (fp) at ambient and elevated temperatures as well as of the heat transfer coefficient (hp) were used to establish the analogy between momentum and heat transfer in gas-solid packed beds of monosized spherical glass particles, as jH=fp/22 or jHε=fp/50. Also, the Chilton-Colburn type of momentum-mass transfer analogy was confirmed. These findings are valid for the range of the modified Reynolds number Re’p≈20-130. The experiments related to fp were performed by measuring the pressure drop across the packed bed of particles (0.58, 0.92, 1.04, 1.20, 1.94, 2.98, 3.91, and 4.91 mm diameters) heated to the desired temperature by hot air (temperatures from 20ºC to 350ºC). The range of gas superficial velocity was from 0.05 to 0.99 m/s, and the bed porosities were from 0.357 to 0.430. The experiments related to hp were performed by recording the temperatures of the cold aluminium test spheres (6, 12, and 20 mm in diameter) with embedded K-type (Ni/Al) thermocouples, immersed into the hot packed bed of particles (1.20, 1.94, and 2.98 mm diameters at temperatures from 100 to 300ºC) until the thermal equilibrium was reached. The superficial gas velocity and bed porosity varied from 0.30 to 0.79 m/s and from 0.392 to 0.406, respectively. A new correlation for the prediction of the heat transfer factor has been proposed in the form jHε=0.30(Re’p)-0.30. The analogies defined in this way leave the possibility of determining the value of the heat and mass transfer coefficients on the basis of the value of the friction factor, which is more common in the literature.

Pyrolysis of Sugarcane (Saccharum officinarum L.) Leaves and Characterization of Products.

The finite nature, regional availability, and environmental problems associated with the use of fossil fuels have forced all countries of the world to look for renewable eco-friendly alternatives. Agricultural waste biomasses, generated through the cultivation of cereal and noncereal crops, are being considered renewable and viable alternatives to fossil fuels. In view of this, there has been a global spurt in research efforts for using abundantly available agricultural wastes as feedstocks for obtaining energy and value-added products through biochemical and thermal conversion routes. In the present work, the thermochemical characteristics and thermal degradation behavior of sugarcane leaves (SCL) and tops were studied. The batch pyrolysis was carried out in a fixed-bed tubular reactor to obtain biochar, bio-oil, and pyrolytic gas. Effects of bed height (4–16 cm), particle size (0.180–0.710 mm), heating rate (15–30 °C/min), and temperature (350–650 °C) were investigated. The maximum yields of bio-oil (44.7%), biogas (36.67%), and biochar (36.82%) were obtained at 550, 650, and 350 °C, respectively, for a 16 cm deep bed of particles of size 0.18–0.30 mm at the heating rate of 25 °C/min. The composition of bio-oil was analyzed using Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and gas chromatography–mass spectrometry (GC–MS) techniques. Several aliphatic, aromatic, phenolic, ketonic, and other acidic compounds were found in the bio-oil. The biochar had a highly porous structure and several micronutrients, making it useful as a soil conditioner. In the middle temperature ranges, biogas had more methane and CO and less hydrogen, but at higher temperatures, hydrogen was predominant.

CPFD study of volatile liquid injection in a dense gas–solid fluidized bed

This study uses the Eulerian-Lagrangian multiphase particle-in-cell (MP-PIC) approach, adopted in the computational particle fluid dynamics (CPFD) code, Barracuda Virtual Reactor®, to simulate the injection of a gas–liquid spray into a gas–solid fluidized bed. The model accounts for evaporation of volatile liquid in the form of individually moving droplets and thin films distributed on the surface of the solid bed particles. Comparison with previously reported temperature measurements for varying spray nozzle gas-to-liquid ratios suggests that the model is capable of predicting the overall features of the gas temperature distributions within the injection region at injection velocities of less than 50 m/s. Locally observed discrepancies between experimental and simulated temperature profiles are likely related to the presence of wet particle agglomerates in the spray region, as suggested by a developed energy dissipation model that, combined with the MP-PIC model, predicts the location and extent of agglomeration in the fluidized bed.

Numerical analysis of drying characteristics of frozen material immersed in fluidized bed at low temperature under reduced pressure

A spherical frozen material was dried in a fluidized bed of inert particles at a low temperature (lower than the melting point of water) under reduced pressure. To evaluate the drying characteristics of the frozen material, the heat and mass transfers in the material during the drying process were calculated using one-dimensional differential equations. The fitting parameters (accommodation coefficient of internal sublimation and heat transfer coefficient at the surface of the material) were determined to fit the calculation results and the experimental data. Drying characteristics, such as the distributions of moisture content and temperature in the material during drying, were calculated. Operational conditions, such as bed temperature, humidity, and heat transfer coefficient (gas velocity) at the surface of the material were varied in the calculation, and the effects on the end time of drying were estimated. Sublimation in the interior of the material governs the drying characteristics. The dry region in the material became resistant to heat transfer. The calculation results are reasonable for expressing the drying characteristics of freeze-drying, that is, our calculation method can be used to estimate the drying characteristics of frozen material in a fluidized bed.