Bed Of Particles Research Articles

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

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

Shaping technical catalyst particles in a bottom-spray fluidized bed

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

Numerical Simulation Study on the Gas–Solid Flow Characteristics of a Large-Scale Dual Fluidized Bed Reactor: Verification and Extension

Dual fluidized bed (DFB) reactor systems are widely used in gas–solid two-phase flow applications, whose gas–solid flow characteristics have a significant effect on the performance of many kinds of technologies. A numerical simulation model was established on the basis of a large-scale DFB reactor with a maximum height of 21.6 m, and numerical simulations focused on gas–solid flow characteristics were carried out. The effects of the superficial gas velocity of both beds and the static bed height and particle size on the distribution of the pressure and solid suspension density and the solid circulation rate were studied. The simulation results were in good agreement with the experimental data. With the strong support of the experimental data, the gas–solid flow characteristics of large-scale DFB reactors were innovatively evaluated in this numerical simulation study, which effectively makes up for the shortcomings of the current research. The results showed that the superficial gas velocity of both beds and the static bed height have different degrees of influence on the gas–solid flow characteristics. Specifically, for 282 μm particles, when the superficial gas velocity of both beds and the static bed height were 4.5 m/s, 2.5 m/s, and 0.65 m, respectively, under typical working conditions, the bottom pressure of the two furnaces was 3412.42 Pa and 2812.86 Pa, respectively, and the solid suspension density was 409.44 kg/m3 and 427.89 kg/m3, respectively. Based on the simulation results, the empirical formulas of the solid circulation rate were fitted according to different particle sizes. Under similar conditions, the solid circulation rates of particles with a particle size of 100 μm, 282 μm, 641 μm, and 1000 μm were 2.84–13.28, 0.73–4.91, 0.024–0.216, and 0.0026–0.0095 kg/(m2s), respectively. It can be found that the influence of the particle size on the solid circulation rate is the most significant among all parameters.

Experimental investigation of wet particle flow characteristics in a pseudo two-dimensional fluidized bed

The flow characteristics of wet particles in a fluidized bed are extremely complicated due to the presence of moisture. It is essential to understand the complex behavior and flow characteristics of wet particles in the drying, coating and granulation process for optimizing the process efficiency and product quality. Thus, the flow characteristics of wet particles, such as pressure fluctuation, bubble size and bubble fraction, in a pseudo two-dimensional fluidized bed were investigated through the multi-resolution time-frequency analysis of the pressure signal combined with the high-speed camera images. Results show that the critical fluidization velocity increases after the particles are wetted, and it shows a slight increase with higher moisture content levels. Besides, there are two main characteristic frequencies, which correspond to the gas-solid flow state of the gas channel and the large bubble in the bed, respectively. Notably, higher gas velocities promote the dominance of large bubbles. And increasing particle moisture inhibits bubble expansion and reduces bubble size, while dense particle areas expand vertically due to enhanced bonding. The bed height increases with the increase of moisture, and the fluctuation of bubble fraction decreases. In the drying experiment, two characteristic frequencies also appear and the pressure drop reduce slightly due to the reduction of water. During the drying process, both the average bubble fraction and fluctuation intensity increase.

Lattice concrete: 3D printed periodic cellular structures through selective cement hydration

3D printing of concrete allows fabrication of complex shapes and structures. Among various 3D printing approaches, the particle bed 3D printing technique has gained attention in recent years, especially for its ability to generate complex topologies that are otherwise impossible to make using cement-paste extrusion-based techniques. In this work, we present our trials on 3D printing cellular lattice concrete structures using a powder bed technique by employing selective cement hydration. Specifically, we print two-types of cellular concrete blocks (i) with interconnected spherical voids and (ii) with gyroid structures, each block with uniform edge lengths of 15 cm. We use Ordinary Portland Cement, fine-grained sand, and normal water, without the use of any admixtures or additives. The printing technology used was custom-made and is quite simple and inexpensive involving a syringe based water jetting on to a powder bed of cement and sand mixture. We discuss the quality of the printed specimens obtained as well as their strength characteristics. An inadvertent observation was made, where a compressive strength gain by a factor of more than 2 was obtained in specimens that were exposed to open atmosphere for a long duration after a 28 day curing period compared to those that were tested immediately after curing. The current study demonstrates the feasibility of fabricating cellular lattice concrete structures that can potentially be useful as programmable metamaterials for civil engineering applications.

Investigation of near-wall particle statistics in CFD-DEM simulations of dense fluidised beds and derivation of an Eulerian particle dynamic wall boundary condition

In two-fluid simulations of gas–solid fluidised beds, the gaseous phase and the particulate phase are modelled as continuous media. The stress exerted by the particulate medium on the container walls should be modelled to predict accurately the bed dynamics. This paper addresses the modelling of sliding particle–wall contacts in two-fluid simulations, based on reference simulations coupling computational fluid dynamics with the discrete element method (CFD-DEM), in which the individual movement of the particles is tracked. The analysis of the CFD-DEM highlights the complex near-wall behaviour of the particles, which is not reproduced by two-fluid models. Nevertheless, the particle–wall shear stress can be expressed based on the total granular pressure within the first cell off the wall. The model is validated for the two-fluid simulation of a bubbling gas–solid fluidised bed of olefin particles in the dense-fluidisation regime.

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

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

Impact of mix proportions on particle bed 3D printed concrete properties

Additive manufacturing of concrete using particle-bed printing by selective binder activation is examined. This technique consists of spreading of a dry powder layer onto the build platform, selective liquid deposition to form a geometry on the layer, and repetition until complete. This enables the manufacturing of complex structural elements and eliminates the need of support structures during fabrication. A commercial liquid-jet 3D printer was modified and used along with a dry mixture of sand, cement, and a specially formulated aqueous solvent. The influence of the proportions of the dry powders, water/cement ratio, type and gradation of sand, type of cements, and additives on the strength and dimensional inaccuracy is examined. The results indicate that the CSA cement with round grain silica sand provides the best mechanical performance and surface quality. The use of a sand/cement ratio of 2.0, printed water/cement ratio of 0.151, and sand fineness modulus of 2.751 produced the best mechanical strength and dimensional accuracy. The results can be used to guide the design for this innovative 3D printing approach for concrete structural elements.

Dynamic in situ measurement of axial segregation of E-CAT particles in a bubbling fluidized bed

The present paper summarizes comprehensive in situ measurements of the temporal segregation/mixing behavior of the non-spherical Geldart B and D E-CAT particles mixture in a bubbling fluidized bed. The experiments are performed for both unsieved and sieved E-CAT particles with varying particle size distribution width and at the fluidization velocity ranging from 1.3 to 5Umf. The high-speed pressure and image data were used to provide time-resolved quantification of dynamic expanded bed height and pressure drop during the experiment. In parallel, a hybrid machine learning-aided image processing algorithm has been developed for quantifying the instantaneous particle size distribution at varying axial locations. Results reveal that the segregation exists only at low fluidization velocities (1.3 and 1.6Umf) for unsieved cases with a wider size distribution. In contrast, particles with a narrower distribution exhibited well-mixed behavior for the full range of tested gas velocities. The segregation intensity and spatial extent were found to correlate with particle size distribution width and fluidization velocity, respectively. In addition, by analyzing pressure, expanded bed height, particle size and motion, and bubble characteristics, we provided a comprehensive multi-scale dynamic view of the segregation process. This in-depth understanding of the process, coupled with the time-resolved datasets obtained, can be instrumental for benchmarking numerical models in solid–gas multiphase flows and for optimizing the design of fluidized beds.

Testing of a 40-kWth Counterflow Particle-Supercritical Carbon Dioxide Narrow-Channel, Fluidized Bed Heat Exchanger

Particle-based primary heat exchangers (HXs) must deliver sCO2 fluid temperatures above 700°C to couple particle-based concentrating solar receivers and thermal energy storage (TES) sub-systems with efficient sCO2 power cycles. Particle-sCO2 HX designs have struggled to meet DOE cost targets (≤ $150/kWth) due to the amount of expensive nickel alloys necessary for manufacturing full-scale, particle-sCO2 HXs. Our team has demonstrated that mild bubbling fluidization of falling particles in a counterflow narrow-channel fluidized bed can reduce required HX surface area and thus, costs by increasing particle-wall heat transfer coefficients hT,w > 800 W m-2 K-1. This paper reports on the fabrication and testing of a stainless steel, particle-sCO2 HX with 12 fluidized-bed channels approximately 10.5 mm deep spaced between diffusion-bonded, micro-channel sCO2 plates. The HX with a core length of ≈0.56 m is fed with CARBOBEAD HSP particles through a short, fluidized freeboard zone just above the core. Testing to date in the National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories has shown that parallel bed fluidization maintains uniform particle inventory across the instrumented channels. Heat transfer thermal duty between the particle and sCO2 flows exceeds 30 kWth with sCO2 inlet temperatures of 200ºC and particle inlet temperatures up to 440ºC and mass flow rates of 0.2 kg s-1 fluidized by counterflowing gas flow rates of 0.005 kg s-1. Tests at higher particle and sCO2 inlet temperatures (600ºC and 400ºC respectively) are targeted to achieve > 40 kWth with model-predicted overall heat transfer coefficients U > 400 W m-2 K-1.

A theoretical model of cross-flow heat transfer for the cooling process in a horizontal moving bed of high-temperature particles

ABSTRACT Besides waste gas and liquid, high-temperature particles are important media of waste heat and their temperature exceeds 1000°C on many occasions. The cross-flow heat transfer is important in this waste heat recovering process, but there are few references reported about the theoretical modeling. Therefore, a theoretical model was developed for the cooling process in a horizontal moving bed of high-temperature particles. The purpose of the study is to estimate the influence of temperature field and flow field on heat transfer and bed resistance in the cross-flow cooling process. Three modes such as conduction, convection and radiation are considered in the model. This model was used to analyze heat transfer in a horizontal moving bed of cement clinker and was verified by comparing some simulative results with the tested and collected data from an actual cement clinker plant in China. The simulative temperature of cement clinker was 200°C as same as that collected in the actual cement clinker plant. In the moving bed, the highest pressure drop occurs at the front top and the strongest heat transfer occurs at the front bottom. In the considered conditions with even distribution of cooling air, the highest pressure drop is 3205.9 Pa/m, the biggest specific heat transfer rate of 1683.1 kW/m3. Thermal radiation plays a minor role in this cooling process with the biggest radiation proportion is only 0.149 at the front top. This mode plays a minor role in this cooling process of the cement clinker, comparing with the thermal convection. With constant flow rate of cooling air, the distribution can regulate the local cooling rate rather than the final temperature of the cement clinker.

Computational fluid dynamic simulation of packed bed drying process: impact of particle properties, drying conditions, and lateral edge heating modes on drying kinetics

In this work, a two-dimensional computational fluid dynamic (CFD) model is developed to describe the drying process of a packed bed made of spherical particles. The volumetrical evaporation rate inside the bed is computed from the pressure difference between the particle surface and the airflow. By using the thermal equilibrium assumption, the heat conservation equation is derived. The CFD model is solved in the COMSOL Multiphysics environment. The obtained results indicate remarkable maldistributions of temperature and moisture content. These maldistributions can be explained by the impact of lateral edges on thermo-hydraulic behavior. Additionally, the impact of particle diameter, air velocity, and bed width on the spatial-temporal moisture content and temperature distribution is investigated. It shows that the CFD model can be simplified to the receding front drying model for a bed made of small particles. Furthermore, by changing the thermal boundary conditions at the lateral edges, the influence of the heating mode at the lateral edges on the drying behavior is explored. The results indicate that contact heating at the bed wall can help to accelerate the drying process significantly.

Nanoparticle surface premelting-induced low-temperature sintering and large shrinkage of particle beds in additive manufacturing

Understanding the thermophysical properties (e.g., thermal shrinkage and thermal conductivity) of the ceramic nanoparticle packed beds in additive manufacturing are crucial for improving the manufacturing accuracy. In this work, we firstly modeled the surface premelting process of nanoparticles, which is likely responsible for low-temperature sintering, and subsequently established thermal shrinkage model of nanoparticle packed beds. The model captures the experimental results well. The results show that with the increase of the sintering temperature, the changing tendencies of both the volume shrinkage (related with accuracy) and the thermal conductivity (related with heat diffusion) of nanoparticle beds all depend on the melting degree of nanoparticles, thus has a same trend. The smaller the nanoparticles, the lower their premelting temperature, thus the lower the sintering temperature of the nanoparticle beds and the greater shrinkage the nanoparticle beds in the additive manufacturing. The porosity of nanoparticle beds which is usually less than 85 % has a neglectable effect on the shrinkage. This work provides methods to predict both sintering temperature in thermal processing and also shrinkage of nanoparticle beds in additive manufacturing.

An Analysis of Fixed-Bed Catalytic Reactors Performances for One-Stage Butadiene Synthesis from Ethanol

The present study assesses, using a theoretical approach, the performances of two widely used fixed-bed reactors for the ethanol-to-butadiene (ETB) one-stage (Lebedev) process: multibed adiabatic reactors (MBAR) with inter-bed heating and a multitubular reactor (MTR). The mathematical model consists of mass and heat conservation equations at catalyst particle and particle bed scales, coupled with a published kinetic model specific for a modified MgO–SiO2 catalyst. The process simulations at the level of catalyst particle have shown that the inter-phase concentration and temperature gradients are negligible, the only physical step with a limiting influence on process kinetics being the internal diffusion. A simplified version of the reactor model was also formulated, including empirical expressions developed in the study for the calculation of internal effectiveness factors. The reactor simulations highlighted that the MBAR with inter-bed heating by injection of hot reactants provides worse butadiene (BD) yields as a consequence of reduced reaction times (due to reactant by-pass of catalyst beds). The MBAR with inter-bed heating using heat exchangers provides better performances but inferior to those of MTR if the number of catalyst beds is less than six. A preliminary optimization study for the MBAR and MTR is also presented. The results showed that the maximization of BD yield has the drawback of a low BD production rate, whereas the maximization of BD production rate corresponds to a relatively low BD yield and high ethanol and inert recycles. A trade-off between the two extreme cases can be attained by maximizing the income generated by reactor operation.

The Impact of Discrete Element Method Parameters on Realistic Representation of Spherical Particles in a Packed Bed

Packed bed reactors play a crucial role in various industrial applications. This paper utilizes the Discrete Element Method (DEM), an efficient numerical technique for simulating the behavior of packed beds of particles as discrete phases. The focus is on generating densely packed particle beds. To ensure the model accuracy, specific DEM parameters were studied, including sub-step and rolling resistance. The analysis of the packed bed model extended to a detailed exploration of void fraction distribution along radial and vertical directions, considering the impact of wall interactions. Three different samples, spanning particle sizes from 0.3 mm to 6 mm, were used. Results indicated that the number of sub-steps significantly influences void fraction precision, a key criterion for comparing simulations with experimental results. Additionally, the study found that both loosely and densely packed beds of particles could be accurately represented by incorporating appropriate values for rolling friction. This value serves as an indicator of both inter-particle friction and friction between particles and the walls. An optimal rolling friction coefficient has been thereby suggested for the precise representation for the densely packed bed of spherical char particles.

Coupled simulation of fluid-particle interaction for large complex granules: A resolved CFD-DEM method for modelling the airflow in a vertical fixed bed of irregular sinter particles

A resolved CFD-DEM method is proposed to simulate the fluid-particle interaction for large complex granules. The airflow in a vertical sinter fixed bed is numerically studied using this method. The multi-sphere clumped method is used to create irregular sinter particles in DEM. The immersed boundary method and dynamic cell refinement are applied to describe the fluid flow around particles with higher resolution, by which the fluid-particle interaction can be simulated more accurately. The simulation results presented the packing voidage distributions and the airflow fields in the sinter beds of different single and mixed particle size ranges. The bed pressure drops were simulated and the results were compared with the corresponding experimental ones. The good agreement indicated that the proposed resolved CFD-DEM method is an effective tool to model the fluid-particle interaction for irregular large granules in the gas-solid multi-phase systems.

Pore-scale modelling of particle transport in a porous bed

A computational study was performed of the transport of both non-adhesive and adhesive particles in a porous bed with a body-centred cubic (BCC) structure. Pore-scale simulation of the flow within the porous bed was achieved through combining the immersed boundary method and the lattice Boltzmann method. Particle transport is computed using an adhesive discrete-element method based on a multi-time-scale soft-sphere model. The fluid flow results are validated by comparison with experimental data for dimensionless permeability of flow in a porous bed of spheres. For computations with non-adhesive particles, the particles are observed to drift to the centre of ‘channels’ in the BCC array, within which most of the fluid flow occurs. The mechanism of this inward drift was found to be related to the phenomenon of oscillatory clustering, which is an inertial drift mechanism observed for particles in a corrugated channel. A measure for particle drift into these channels was developed, and the time rate of change of this measure was found to compare closely with an approximate theoretical prediction based on oscillatory clustering theory. The drift measure was observed to be limited at long time by hold-up of outlier particles caught in long-duration collisions with the fixed bed particles in regions of low fluid velocity magnitude. Simulations with adhesive particles exhibited marked increase in collision duration, as well as inhibition of the tendency to drift toward the flow channels due to adhesive hold-up.

A DEM-CFD Approach for Predicting Pressure Drop Through Packed Bed of Crushed Rocks

Predicting the pressure drop over a packed bed of air-crushed rocks is a crucial parameter for a solar storage system to be economically viable. The selection of the blower and the estimation of the total capacity of the storage system are highly dependent on it. There are various parameters that influence the air flow through the bed, such as the shapes and sizes of the crushed rocks, which affect the packing density and particle arrangement. In this paper, the crushed rock was represented by an ellipsoidal shape with the same volume and aspect ratio as the average of randomly collected crushed rock samples to investigate the pressure drop through the packed bed. Simulation models were developed to assist in driving a pressure drop correlation as well as the effect of particles' orientation on pressure drop. For simulation, a Discrete Element Model (DEM) was used to generate the particles and Computational Fluid Dynamics (CFD) to simulate the flow over the particles. To validate the DEM/CFD models, experiments consisting of a packed bed of ellipsoidal particles and crushed rocks were developed. Consequently, an equation based on the porous media approach was proposed to predict the pressure drop, and the correlation was found to underestimate the pressure drop through the crushed rock by less than 20% in the horizontal flow.

Segregation of binary particles in pulsed gas-solid fluidized bed

Pulsating airflow-driven gas-solid fluidization is an effective method to segregate particles of different densities. The current article presents an elaborate computational study on the development of simulation methodology, and parametric trend identification of pulsating airflow-driven granular segregation for the first time using computational fluid dynamics (CFD), discrete element modeling (DEM) coupled analysis. The rigorous validation of the computational prediction has been produced against the experimental result reported by Li et al. (2021) and an excellent agreement has been observed. Segregation behavior for different density ratios of particles, different patterns of pulsation, and different particle shapes is presented in the current article. The segregation index improves with the density ratio of the binary mixture of particles, but the rate of increment of the segregation index is highly dependent on the airflow rate. Near the optimal value of airflow rate, the rate of increment of the segregation index reduces with the density ratio. Keeping the bed height and material property constant, different patterns of pulsation namely—sinusoidal, triangular, and exponential have been adopted. The segregation index is higher for sinusoidal patterns, whereas it reduces when the pattern is changed to triangular and exponential. Particles of constant volume with different shapes are also considered to understand the effect of particle shape on segregation. The segregation index deteriorates with the increasing surface area of the particle at constant volume.

Study on density distribution characteristics and fine coal separation of magnetically fluidized beds of microfine particles

ABSTRACT In this paper, the characteristics of the axial and the radial density distribution and the density stability of a gas-solid fluidized bed formed by microfine magnetite powder were studied under different fluidizing gas velocities and magnetic field intensities, and the separation experiments of −6 mm fine coal were carried out. The experimental results show that the axial density of the bed with magnetic field applied is lower than that without magnetic field applied under different gas velocities. The density fluctuation of the gas-solid fluidized bed with magnetic field is smaller than that of the ordinary gas-solid fluidized bed, and the stability of the bed density decreases with the increase of the fluidization number. The experimental results of separation of −6 mm fine coal show that the Ep value increases with the increase of fluidization number. Under the same fluidization number, the Ep value of −6 + 3 mm coal is smaller than that of −3 + 0.5 mm coal. When the fluidization number is 1.1, the Ep value of −6 + 3 mm coal is 0.0375 g/cm3, and the Ep value of −3 + 0.5 mm coal is 0.0475 g/cm3. This shows that the magnetically fluidized bed of microfine particles has a good separation effect for −6 mm coal.