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The utilization of hydrogen is gaining increasing attention due to its high heating value and environmentally friendly combustion product. The supercritical water circulating fluidized bed reactor is a promising and potentially clean technology that can generate hydrogen from coal gasification. Cyclone is a vital part of the reactor which can separate incomplete decomposition of pulverized coal particles from mixed working fluid. This paper aims to gain in-depth understanding of the cyclone separation mechanisms under supercritical fluid by computational fluid dynamics (CFD). Although the amount of supercritical carbon dioxide in mixed working fluid is minor, it obviously influences the flow fields and separation efficiency of a cyclone. The simulation results suggest that both the decreasing content of supercritical carbon dioxide and adding the extra dipleg cause the promoting performance of cyclones. Research findings could refine the design of supercritical fluid–solid cyclones.

Non-uniform sand retention behavior often occurs to the serviced screen deteriorating erosion. However, this phenomenon is poorly understood. This paper presents a numerical study of the sand retention on wire-wrapped screens, with special reference to non-uniform behaviors. This is done by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM). The validity of the model has been validated for dry and wet sand screen systems. It is used here to study sand retention behaviors at different solid concentrations and particle size distributions (PSD). Via this model, five distinct sand retention modes are identified: No sand retention (Mode I), partial sand retention (Mode II), sand retention with slow sequential bridging (Mode III), sand retention with fast sequential bridging (Model IV) and sand retention with instantaneous bridging (Mode V). Modes II and III belong to non-uniform sand retention, which develops strong local flows that induce local erosion or hot spot on the screen. A phase diagram is introduced to predict these five modes and their transition with respect to solid concentration and PSD. Additionally, the predicted flow and force structures are analyzed in detail. The results indicate that the bridging over a slot heavily relies on the particle accumulation on the screen. A new screen with a converging slot configuration is proposed to improve this particle accumulation. This improvement helps develop uniform sand retention on the screen.

This study focuses on the combined effect of particle shape and porosity on the momentum and heat transfer of granular matter under laminar flow. Particle-resolved direct numerical simulations (PR-DNS) are carried out at different working conditions. Numerical results show that both the particle shape (via the aspect ratio, Ar, of the spheroid) and porosity play important roles in affecting the drag coefficient (Cd) and average Nusselt number (Nu). The influence of particle shape on Cd and Nu is regardless of the particle porosity. It is found that the Cd decreases with the increase of Ar for a given Reynolds number (Re). The Nu decreases with the increase of Ar under high Reynolds number (100

The oxy-fuel co-firing of solid fuels (such as coal, biomass, and solid waste) in fluidized beds is one of the most promising technologies for the industrial application of CO2 capture and waste disposal. However, both the practical experimentation and numerical simulations for elucidating co-firing in an oxy-fuel fluidized bed are still limited. In this study, a multiphase particle-in-cell scheme based on a 3D Eulerian–Lagrangian model was further developed following our previous research on oxy-fuel co-firing in a micro fluidized bed (Powder Technol. 2020, 373, 522–534). The refined JL 4-step mechanism for the CO-CO2 homogeneous reactions, the heterogeneous reactions of char oxidation and gasification, the heterogeneous reactions of NO and N2O formation from char-N, and the self-desulfurization effect were comprehensively considered. The improvement of the models was verified through the continuous operation of 10 kWth oxy-fuel fluidized bed tests (Fuel 2021,286,119,312; Energy Fuels, 2020, 34, 7373–7387), and the effects of the biomass blending ratio (Mb) on co-firing characteristics were discussed. It was found that the improvements could enhance the adaptability of the models to the oxy-fuel atmosphere, and the accurate prediction of NO, N2O, SO2. With an increase in Mb, the main reaction zone expanded or moved up along the riser height, and the volume of the high-temperature area increased, which promoted the burnout of particles and CO2 emission when Mb is 50%. The high volatility of biomass increased O2 consumption and CO concentration at the upper part of the riser, reduced N2O formation, and had a significant impact on NO reduction. The low sulfur content and high Ca/S ratio of the biomass considerably reduced the SO2 concentration. The simulation results also provided helpful information for the design and operation control of oxy-fuel co-firing of coal and biomass in a fluidized bed, such as the oxidant supply in different areas and grades, appropriate increase in the riser height, and reasonable adoption of Mb.

Discrete element method is used in this work to examine the mechanisms determining powder deposition efficiency during powder spreading in powder bed fusion additive manufacturing. The results reveal that powder flow in the powder pile is critical for the formation and break of transient jamming. The forces on the underlying part increase first with spreading speed then decrease with a large fluctuation. For varied spreader shapes, a small inclined angle of the spreader surface makes the force barrier farther from the discharging gap, creating a larger region which ensure enough powder supply to the gap. Furthermore, a small inclined angle of the spreader surface close to the gap results in less particle motion conflicts at the gap and ensures larger discharging rate through the gap. This mechanism explains why spreaders with inclined or round surfaces help increase powder deposition efficiency.

In this work, a low-temperature electrostatic precipitator (ESP) experiment platform was established, and two different electrode configurations were compared under various operating parameters to obtain a method for increasing particle capture efficiency. Results show that, in the case of the rated current, the voltage is significantly affected by temperature variations. Concurrently, by appropriately reducing the flue gas flow velocity of the ESP, the charging time of the particles in the ESP flue can be increased, fully charging the particles and improving the collection efficiency. Moreover, experiments revealed that increasing the relative humidity during ESP operation will increase the particle migration velocity and collection efficiency. Finally, when the electrode configurations were changed from a flat collection plate and round electrode to a sharper needle electrode and a concave-convex structure BE plate, resultantly, all efficiencies exceeded 85% under the temperature range from 50 to 150 °C.

Bends are potentially most problematic in a hydraulic conveying pipeline system. This paper presents a numerical study of hydraulic bends, with special reference to the interaction between pipe orientation and flow regime. This is done by the combined approach of computational fluid dynamics and discrete element method facilitated with a wear model. The validity of the model has been verified by comparing the measured and predicted flow properties and erosion depth. On this basis, three pipe orientations: 0° (i.e. horizontal-vertical bend), 45° (i.e. inclined bend), and 90° (i.e. vertical-horizontal bend) are simulated for the conveying speeds of 1.2 m/s, 2.0 m/s and 4.0 m/s. It covers typical flow regimes in a horizontal pipe. Via the simulation outputs, the bend performance is assessed in terms of pressure loss, conveying instability and bend erosion. The results reveal that the pressure drop and erosion rate differ for various pipe orientations and conveying speeds involving different flow regimes. The acceleration/de-acceleration of the particles exiting the bend does not result in a significant additional pressure. The vertical-horizontal bend has low erosion rates benefiting from cluster formation and low pressure, which is not the case at high conveying speeds. By contrast, the inclined bend gives the highest elevation height and does not suffer significant pressure drop, pressure fluctuation, and erosion rate under all the flow regimes considered.

The minimum fluidization velocity of a supercritical water fluidization bed reactor (SCWFBR) is numerically nvestigated based on coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations. The accuracy of the CFD-DEM model is firstly validated via previously published experimental data. Then, the model is adopted to study the effects of particle size distributions (PSD) on the minimum fluidization velocity in which four types of PSD including Gaussian-type, Mono-type, Flat-type and Binary-type are considered. Numerical results show that the minimum fluidization velocity for the Flat-type PSD is the smallest among the four while the one for the Mono-type PSD is the largest. The minimum fluidization velocities for the Mono-type and Gaussian-type PSD share quite similar values. However, it is conditionally valid when the largest amount of particle size in the Gaussian-type PSD is equal to its mean particle size which is used in the Mono-type PSD. The agreement of the minimum fluidization velocity between Mono-type and Gaussian-type PSD is also influenced by the number of small particles. The mechanism behind these phenomena is revealed by investigating the micro-structure of differently sized particles. Finally, predictive correlations for the minimum fluidization velocity of the SCWFBR are proposed based on the numerical results which demonstrates strong predictive capability for wide PSD.

With increasing social concern towards industrial wastewater treatment, desulfurization wastewater evaporation technology is attracting attention in theoretical investigation and showing competitive capability in practical applications by virtue of its low cost and high efficiency. In engineering practice, the selection of nozzle model, evaporation chamber size and flue gas source need to be carefully determined, ideally with comprehensive understanding of the process mechanism. Important factors to be considered include wastewater evaporation characteristics such as evaporation time, distance, and so on, which are difficult to be obtained directly through physical experiments. Numerical simulation can be utilized conveniently for the extraction of such data and further post analysis. In this study, a salt containing droplet evaporation model is combined with a two-way interphase coupling method to investigate the spray evaporation process. Numerical results show that by increasing the injection velocity and the liquid film thickness, and reducing the flue gas velocity, droplets were observed to be more dispersed in the flue, which in turn enhance the evaporability. The velocity difference between the gas-liquid phases is correlated with the gas-phase turbulent kinetic energy. Non-uniform inlet velocity can increase the flow turbulence intensity. This leads to enhanced droplet evaporation performance on one hand, but increased probability of the droplets hitting the wall on the other hand. From this study, we have also observed that the droplet evaporativity increases with the temperature. Finally, an optimal set of parameters are selected from the simulation exercises to achieve an optimal evaporation outcome. These parameters are introduced in large engineering design to guide the selection of the nozzle model and determine the evaporation chamber size.

This paper aims to establish the relationships between microscopic and macroscopic properties for uniform sphere packings under gravity. The packings are generated by the discrete element method under different conditions with the packing density ranging from about 0.2 to 0.74. The microscopic properties are the structural properties commonly used, including coordination number and various topological and metric properties from the Voronoi-Delaunay tessellation. The results show that these properties can be correlated with packing density. The correlations can be used to estimate different structural properties which are otherwise difficult to obtain in practice.

Packing properties are determined by the dynamic deposition history and affected by many variables. In this work, DEM is used to study the effects of dropping height, deposition intensity and friction coefficient on the dynamic response and stable-state packing properties of ellipsoidal particles. The results demonstrate that with dropping height increasing, packing density increases but the bed becomes less ordered. Dropping height affects the densification process of ellipsoids more significantly than spheres. At high dropping height, the transition period of the orientation angle in the densification process almost disappears for oblate particles, while it becomes longer for prolate particles. With the increase of deposition intensity, packing density decreases significantly, but orientational order changes slightly. With the increase of sliding friction coefficient, packing density and orientational order decrease dramatically. The difference in packing density is mainly caused by dynamic pouring process rather than the densification process.

Powder spreading process is to use a spreader such as blade or roller to spread powder layers for subsequent fusion in powder bed fusion additive manufacturing. In this work, the effects of various spreader geometries on powder spreading are examined by discrete element method (DEM). The results show that a compact region in the powder pile exists. Round and inclined surfaces of blade spreaders allow more particles in the compact region to be deposited compared with vertical blades, thus the powder layer formed is denser. However, they exert larger forces on the underlying part. Inhomogeneity of powder layers is caused by particle burst phenomenon, which is due to particle motion conflict in the compact region rather than large forces. Roller system has largest particle motion conflict thus powder layers formed are sparse and inhomogeneous with small layer gaps. Size segregation in blade systems is not as severe as roller systems.

GPU-based DEM is used to study large-scale particle mixing in bladed mixers. A bladed mixer is scaled-up to three different sizes by maintaining the geometric similarity. Four Froude numbers are selected as the main operating conditions of bladed mixers with different sizes. The results demonstrated that the mixing quality across different mixer sizes is similar at the same Froude number, but it requires a longer mixing time to achieve similar mixing performances as the mixer becomes larger. Correlations to predict the mixing rate, average particle velocity, average total forces, average contact forces and average blade torque as functions of the scale-up ratio and Froude number (or rotation speed) are proposed. A similarity study shows that maintaining the dynamic or kinematic similarity does not produce a similar mixing performance, while maintaining the mixing rate produces a similar mixing performance across all mixers.

This paper presents a numerical study on the self-assembly of mono-size granular spheres with periodic boundary conditions under uniform and non-uniform 3D vibration. For uniform 3D vibration, the vibration conditions for self-assembly are similar to those under 1D vertical vibration. For non-uniform 3D vibration, slight horizontal vibration added to 1D vertical vibration can significantly promote or depress self-assembly. Moreover, under 1D or uniform 3D vibration, self-assembly results in a RHCP (random hexagonal close packed) structure, while under certain non-uniform vibration, a packing can self-assemble into a nearly pure FCC (face centered cubic) or HCP (hexagonal close packed) crystal structure. The microscopical analyses on the local structures, dynamics and forces provide rich insight into the different self-assembly processes under different vibration modes. These results can help understand the self-assembly of granular materials under vibration and guide how to control the structure of packed beds.

It has been a longstanding question how stars are packed or distributed in the universe. Here we show that the spatial distribution of stars follows some geometric rules although there may be local inhomogeneities. The topological and metric properties of their Voronoi tessellations exhibit a lognormal distribution. Moreover, these distributions can be connected with those established for the packing of spheres, corresponding to the loosest packing state. The findings provide a new angle to understand the packing structure of stars in the universe.

Laser powder bed fusion (LPBF) is one of the most promising additive manufacturing technologies to fabricate high quality metal parts. In this work, a three-phase model based on the volume of fluid (VOF) is employed to investigate the heat transfer and melt pool behaviour in LPBF. Surface tension, Marangoni effect and recoil pressure are implemented in the model, and heat adsorption, reflection and transmission are fully considered. The results show that the melt pool dimension and its shape are controlled by laser power and scanning speed. Metal powders at the bottom layers may be not fully melted, and for larger layer thickness of the powder bed, porosities caused by the trapped gas can form. The gas originated from bulk powders can dissolve, coalesce, and be squeezed in the melt pool. It is demonstrated that the model can capture the main features of powder melting and solidification in LPBF process.

Coordination number (CN) is an important microscopic parameter in describing the packing of particles. There are a few mathematical models proposed in the literature to calculate the CN of a particle mixture. However, they have not been comprehensively assessed as the experimental data are limited. In this paper, the applicability of three models, respectively proposed by Dodds, Ouchiyama & Tanaka, and Suzuki & Oshima, is assessed against the results recently generated by means of discrete element method. The results indicate that the model of Ouchiyama & Tanaka differ from the simulated CNs significantly, thus not recommended. The other two models produce similar results, but the Dodds model is probably more reasonable. In particular, these two models are able to estimate the variation trend of the average CN for various particle size distributions but their predictability reduces with the increase of particle size difference. The Dodds model becomes numerically unsolvable when the small-to-large size ratio is smaller than 0.154. Therefore, modification of the existing models or development of a new model is required in future studies for better prediction of the CN of the packings of multisized particles.

A new conical-cylindrical top-discharge blow tank is designed, by introducing the pulsed gas to facilitate discharging, for stable transportation for kaolin powders. A series of experimental studies on pulsed gas characteristic parameters like pulsed gas flow rate Qpulsed (5 m3/h ≤ Qpulsed ≤ 25 m3/h), pulsed interval tpulsed (1 s ≤ tpulsed ≤ 5 s) and pulsed width τpulsed (50 ms ≤ τpulsed ≤ 250 ms) are conducted with the fluidized gas flow rate of 12 m3/h. The experiments mainly test the powder mass flow rate and solid-gas ratio in the conveying process. The results indicate that the mass flow rate and solid-gas ratio range 12.6–278.04 kg/h and 0.9–19.56 kg/m3, respectively. With the increase of the pulsed gas flow rate, the mass flow rate and solid gas ratio first increase and then decrease. When the ratio of fluidized gas flow rate to pulsed gas flow rate is within 0.8–1.2, its conveying capacity reaches the maximum. Meanwhile, the increase in the pulsed interval leads to the decrease of the mass flow rate and solid-gas ratio. Moreover, the increase in the pulsed width leads to the initial increase and then the stabilization of the mass flow rate and solid gas ratio. When the pulsed width is 50 ms, the improvement of discharge would small. Conversely, increasing the pulsed width can increase the discharge, and stabilize subsequently until over 200 ms. Besides, moisture content is one of the important factors affecting kaolin powders discharge. When the moisture content is 0.83%, the pulsed gas does not improve the discharge significantly. Meanwhile, pressure distribution at different locations in the tank is also measured. The results reveal that the introduction of pulsed gas changes the pressure distribution in the tank. A pressure zone is formed on the upper part of the tank, which promotes the powder discharge.

Sand screens are widely used to control sand production in unconsolidated reservoirs. Because of the lack of insightful understanding of this process, to date, reliably optimizing screen size is still a challenge. This paper presents a numerical study of the sand retention and production behaviors for widely used wire-wrapped screens by means of the combined approach of computational fluid dynamic (CFD) and discrete element method (DEM). The validity of the model has been verified by comparing the predicted critical slot sizes and sand production with published experimental results. On this basis, the effects of slot width-particle size ratios and wetting fluids, including gas and crude oil, are studied. The numerical results show that the increase in size ratio increases sand production, and the presence of fluid flow enhances sand production and causes unstable sand retention, which is more significant for crude oil compared to gas. Also, three mechanisms that allow the sand retention over a screen are identified, including stable bridging, bridging with intermittent collapse, and bridging with continuous collapse. Wetting fluids play an essential role in the sand production and bridging when the particle-fluid forces exerted on the particles near the slot are significant. Such forces induce strong localized particle-particle interactions in the nearby region over the slot, which accounts for the unstable bridging behavior.

This research experimentally studied the granular flow in the optimised curved hoppers obtained from our recently published optimisation method. A series of optimised hoppers were manufactured by CNC machining and an experimental apparatus was constructed to measure the MDR of various granular materials in the hoppers. Our experiment confirmed that the MDR of the optimised curved hoppers has increased more than 100% from that of those conventional conical hoppers. The critical prefill level for reaching a steady discharge rate in the curved hoppers is related to a fixed ratio to the diameter of the hopper orifice, which increases with the initial half-angle of a curved hopper. Three types of granular materials, i.e. rice, urea powders and sands, differing in shape, density and surface roughness, all gained improved MDR in the same curved hoppers, which demonstrates the flexibility of the optimised curved hoppers to maximize MDR for different granular materials.

Understanding the deposition mechanisms of pharmaceutical aerosol in the mouth-throat (MT) is crucial to developing an in vitro method which aims to better predict in vivo lung deposition. This paper investigated the effect of geometrical variation, particle size and airflow rate on the fine particle deposition in the US pharmacopeia throat (USP), idealized mouth-throat (IMT) and realistic mouth-throat (RMT) models. The flow-field equations were solved with the SST model by computational fluid dynamics (CFD) and monodispersed particles in the size range of 1–30 μm were tracked with discrete phase method (DPM). The results indicated that the deposition fraction and spatial distribution were highly sensitive to the geometrical variation and respiratory conditions such as the inhalation airflow rate and particle size. Moreover, the effect of geometrical variation on the particle escape pattern was more dominant. Comparing to the IMT model, more uniformly distribution of escape particles was observed at the outlet of RMT. While the total deposition fractions in IMT and RMT were similar, the spatial distributions of deposited particles were significantly different. In the RMT model, fewer particles were deposited in mouth and trachea, but the depositions in the pharyngeal and laryngeal regions were more uniform. These conclusions could help study the in vitro-in vivo correlation of dry powder inhaler systems.

In granular flows, particles can mix or segregate owing to their difference in size/density. This behaviour is commonly understood as a size- or density-driven segregating flux at the macro scale and has been studied before in systems of shear cell and chute. This work aims to model the segregation in practical systems with complex geometries and flow modes, by coupling the fundamental flow rheology and the convection-diffusion-segregation transport equation. The model is validated against experimental measurements and discrete element simulations in various flow scenarios, shown able to capture the notable characteristics of particle segregation reported, such as the core of small particles in a rotating drum. The predictions can overall match the benchmark tests although the quantitative accuracy still varies with cases, indicating the need for further study. The proposed approach, not limited by operational or geometrical conditions, provides a useful tool for the design and control of mixing processes.

In an ironmaking blast furnace top, raw granular materials such as iron ore and coke are delivered to the parallel Paul-Wurth (PW) hoppers first and then discharged to the furnace. In this work, the effects of variables such as filling positions and filling angles on the size segregation during PW hopper charging and discharging processes are examined. Results illustrate that small particle gathering area appears near the filling points due to the rolling mechanism, and the area size is related to the distance of filling position to the side wall. Trajectory is another main segregation mechanism related to different filling angles. Steep filling angle changes particle trajectories significantly and large particles tend to gather in the side wall region. Increasing flow rate decreases the segregation. During the discharging process, a depression appears and large particles are engulfed in the depression, leading to the segregation at the last stage of discharging.

The heterogeneous structures of the gas-solid flow in riser and downer reactors determine reactor performance but are not fully understood. This paper presents a numerical study of the hydrodynamic characteristics of cohesive particles in a riser and a downer. This is done by the combined approach of discrete element method (DEM) for particles and computational fluid dynamics (CFD) for the gas phase. The numerical results show that this CFD-DEM model can reproduce different annular dense distributions of particles in the fully developed sections of the riser and downer. This realization requires suitable periodic boundary conditions applied to both the gas and solid phases in the flow direction as well as adequately fine meshes. The flow behaviors are analyzed in detail in terms of particle flow pattern, cluster behaviors, gas and solid velocities and forces acting on particles. Also, the dependence of the dense solid ring in the downer on some pertinent variables related to pipe geometries, material properties, and operational conditions is examined.

Particle resolved direct numerical simulations (PR-DNS) are conducted to study the forced convection process of a cold flow passing over a rotating hot ellipsoidal particle. The numerical model is firstly verified against previously published data on both stationary and rotating particles. Then, one hundred case studies are carried out by changing five particle aspect ratios, five Reynolds numbers and four particle spin numbers, respectively. The effects of particle rotation on drag coefficient (Cd), lift coefficient (Cl), moment coefficient (Cm) and average Nusselt number (Nu) are investigated in detail. The changing trends of Cd, Cl, Cm and Nu with the particle incident angle in different cases are comprehensively analysed and compared. Numerical results of a rotating non-spherical particle show quite interesting and different phenomena compared with the stationary case. It is indicated that the particle rotation must be considered when evaluating the momentum and heat transfer between non-spherical particles and fluids. The findings provide important evidence to properly evaluate the role of particle rotation in the macro-scale modelling of multiphase flows.

The co-firing of coal and biomass in fluidized beds under oxy-fuel conditions is an important approach with significant industrial prospects, for both carbon dioxide capture and disposal of biomass waste produced by agriculture and forestry. Numerical simulation is essential in the design of structural and operational parameters for oxy-fuel fluidized beds, as is experimentation. Following our previous research on the oxy-fuel combustion of coal in a fluidized bed (Powder Technol. 2019, 349, 40–51), this paper develops 3D Eulerian-Lagrangian simulations for the co-firing of coal and biomass in an oxy-fuel fluidized bed based on the multiphase particle-in-cell (MP-PIC) scheme. The particle field is described by the discrete particle method (DPM) and the gas field is calculated by large eddy simulation (LES). Different models are used for the reaction of coal and biomass, including devolatilization, combustion of char and volatiles, and the production of pollutants. The numerical simulation was verified by combustion experiments carried out in a micro-fluidized bed reactor with an online mass spectrometer. Based on the simulations, the effects of biomass mass ratio, combustion atmosphere, oxygen concentration, and combustion temperature on the co-firing of coal and biomass in an oxy-fuel fluidized bed are discussed.

Different flow regimes may take place during hydraulic conveying but are not fully understood. This paper presents a numerical study of the horizontal hydraulic conveying of coarse particles by means of the combined approach of computational fluid dynamics (CFD) for the liquid phase and discrete element method (DEM) for particles. The validity of the model is first verified by comparing the measured and predicted radial profiles of solid volume fraction under different operational conditions. On this basis, the model is used to predict the flow regime transition and the corresponding pressure characteristics as the conveying speed increases keeping a constant feed solid volume fraction. It is observed that the flow regimes transit from the stationary-bed flow, through the moving-bed flow, and finally, to the heterogeneous-suspension flow, which is consistent with the experimental observation in the literature. The numerical results are analyzed in detail in terms of flow and force structures. A new phase diagram in terms of the forces acting on particles is proposed to identify flow regimes and their transition. Based on the simulation data, correlations are formulated to predict the pressure drop of the horizontal hydraulic conveying considered.

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.

High-density Bi2O3 ceramics were prepared via a three-step cold sintering process (TS-CSP) at an ultra-low temperature. In the first step, the relative density of the Bi2O3 ceramic, subjected to 155 °C and 300 MPa for 25 min, is 96.23%, with the majority of the crystals inside the ceramic. The Bi2O3 ceramic was further densified with a corresponding increase in the relative density to 98.52%, after processing at 210 °C and 300 MPa for 25 min, in the second step. Finally, in the third stage of the processing, the temperature was raised from 210 °C to 270 °C and isothermally held for 25 min, which enabled the Bi2O3 ceramic grains to fully grow to yield a grain size of 4.02 μm, having a relative density of 99.13%. The densification mechanism of the TS-CSP Bi2O3 ceramics is via a dissolution-recrystallization-growth process. The relative permittivity, quality factor and grain size of the Bi2O3 ceramics are 33.44, 16,218 GHz and 4.02 μm, respectively. The materials and their preparation described herein provide a novel approach for the preparation of ultra-low temperature ceramics.

The oxy-fuel combustion CFB technology as a promising carbon capture technologies needs to study the scale-up process for the commercial diffusion. Numerical simulation would be a rational tool to investigate the gas-solid flow and oxy-fuel combustion process before constructing an expensive and complicated industry-scale plant. A three-dimensional (3D) CFD simulation according to the Eulerian-Lagrangian approach was applied to simulate the hydrodynamics of gas-solid flow and oxy-fuel combustion process in lab-scale, pilot-scale and industry-scale CFB boiler (from 0.1 MWth to 330 MWe). Results present the differences of the boiler configuration, the gas-solid flow and the oxy-fuel combustion characteristics between lab-scale, pilot-scale and industry-scale CFB boilers. The cross-section thermal load gradually decreased, while the cross-section area increased with the thermal inputs increased. In the lab-scale and pilot-scale oxy-fuel CFB, the particle velocity field was more uniform than that in the industry-scale CFB. The carbon conversion ratio increased with an increase in the thermal input. The emission of CO, NO and SO2 in the industry-scale oxy-fuel CFB boilers was lower than those in the lab-scale and pilot-scale. A larger oxy-fuel combustion power plant is beneficial to carbon capture and low pollutant emission. The results would be beneficial to the design and operation of industry-scale oxy-fuel CFB.

Selective Laser Melting (SLM) is a rapidly developing and advanced manufacturing method for fabricating complex products. In SLM, the powder spreading process is crucial to ensure that the right amount of material can be fully melted by a certain laser energy input in order to minimise defects and achieve the desired microstructure. The packing density and homogeneity of the formed powder bed are of interest when comparing melting efficiency and quality of SLM processes with different metal powders or different spreading methods. Particle-based numerical studies are required for identifying the powder bed structure and particle dynamical behaviours which are affected by particle adhesion. In this work, experiments on powder packing density and repose angle for different particle size distributions are carried out. The discrete element method (DEM) model is validated and calibrated based on experimental results. The DEM is then used to examine the powder spreading process, focusing on the effects of particle adhesion and particle-based behaviours. Effects of spreader type, adhesion magnitude and particle size distribution are analysed. The results show that particle adhesion can reduce powder packing density and smoothness of the powder bed surface. Proper adhesion effects can improve powder bed homogeneity. Powder bed structure is determined not only by adhesion effects but also by particle rearrangement during spreading. Regarding spreader type, the roller can spread a better powder bed than rigid blade due to different particle contact force distributions and particle velocities in the powder pile and powder bed, which lead to different particle rearrangements and particle contact conditions.

The transition of a liquid bridge profile from convex to concave and the associated capillary forces are experimentally studied via particle-particle and particle-plane pairs. The results demonstrate that a convex liquid bridge appears at a relatively large water volume and small separation distance, where the capillary force remains approximately constant. As the separation distance increases, the liquid bridge is stretched from convex to concave, and the capillary force initially doesn't change much but increases to the maximum value and then decreases gradually. By combining analytical analysis and experimental data, a framework is proposed for predicting the evolution of liquid bridge profiles. Additionally, a capillary force model that is applicable to both convex and concave liquid bridges is formulated. The applicability of this force model to multiple-particle systems is demonstrated by comparing DEM predictions of repose angles of sandpile and hopper flow discharge rates with experimental measurements at various water contents.

Continuum description of particle-fluid flows is of fundamental importance. In the past, various averaging methods were developed to derive local quantities directly from particle scale information. However, it is not clear if the long-sought resolution-independence of the local quantities exists. Here, using a discrete element method, a statistical analysis is conducted for a gas-solid fluidized bed of monodispersed coarse particles under various conditions. The mean free path and time are first examined with the variation of inlet gas velocity. Then, the particle motion is analyzed according to the Langevin equation and it is revealed that the motion of individual particles in the driven system follows the fluctuation-dissipation relation. Finally, the particle collisional frequency and velocity distribution are analyzed. These distributions can achieve a steady state. The particle collisional frequency distribution deviates from the Gaussian distribution noticeably at high gas velocities. These findings lead to a better understanding of particle motion in a gas-solid fluidized bed and support the seeking of resolution-independent local quantities with averaging methods.

Dust emission due to air entrainment in falling solids/particle plumes is a common and serious environmental issue in industry. The prediction of the flowrate of air induced by falling particles is pivotal for the design of dust removal equipment in practice but until now there is still limited reliable correlations available. In this work, the process of air entrainment in falling plumes of particles is numerically studied by a combined approach of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) (CFD-DEM). A 2D CFD-DEM model is first compared against two 3D models. Then the 2D model is validated against experiments qualitatively at small scale and quantitatively at large scale. Finally the model is used to predict the effect of various important variables including drop height and solids mass flowrate at an industrial scale.

Mass discharging rate (MDR) is a critical aspect of hopper’s performance in bulk solids handling. A shape optimization method is established in this study to increase the MDR of cohesionless granular materials from hoppers. This method is based on a continuum model of granular matter and the Eulerian Finite Element Method (FEM) which can efficiently simulate the discharging process and predict the MDR. In this work with the focus on conical hoppers, the widths of silo and hopper outlet as well as the vertical height of hopper are fixed. The meridian of the hopper, however, evolves from a straight line to some optimal curve, guided by a combined genetic algorithm (GA) and gradient descent method (GDM). Cubic spline function is employed to parametrize the hopper shape. The effectiveness of the shape optimization is examined by comparing the MDRs of the optimal hopper and conventional conical hopper, obtained by both FEM and discrete element method (DEM) respectively. It is shown that this shape optimization method can automatically search the optimal shape of the hopper in a given range of constraints, and increase the MDR substantially. In a typical hopper with an initial half angle of 45°, the MDR is increased by over 130% after the shape optimization. Notably, the optimal shape depends mainly on the geometrical factors, i.e. the allowed width and height for the hopper, whilst insensitive to the material properties, which favors its general use for different particles. Such curved hoppers are particularly useful for increasing the discharge rate of hoppers ranging from 30° to 50°, which, facilitated with advanced manufacturing technology, will find wide potential applications in bulk solids handling.

This paper presents a numerical study of dense-phase horizontal pneumatic conveying of powders by means of Computational Fluid Dynamics (CFD). The validity of the numerical model is first verified by comparing predicted pressure gradients with both published laboratory and industrially measured data. Then, effects of gas superficial velocity, solids loading ratio and pipe diameter on the flow regime transition and dune formation in horizontal pipes are investigated. Results show that dune, stratified and suspension flow regimes can be successfully reproduced. The transition of the suspension flow to the dune flow is determined mainly by the proportion of gas and solid phases. With increasing pipe diameter, the dune flow changes to the stratified flow. Also, flow characteristics are analyzed with respect to different flow regimes. It reveals that the formation of the dune flow is due to the intensive interaction between suspension and accumulation zones through a contact zone.

Graphics processing unit (GPU)-based DEM combined with message passing interface (MPI) has been applied to large-scale handling and processing systems, including granular conveying, reclaiming, screening, ship loading, grab and screw unloading, and blast furnace top charging systems. The issues in terms of particle flow behaviour, particle-wall interaction/wall stress, particle energy dissipation, size segregation, and process efficiency, etc., are discussed. The results showed that for a belt conveying chute, wear became more severe at higher flow rates. In the reclaiming process, there was an increase in the digging resistance on the buckets with increasing bucket rotation speed. For the screening process, lower vibrating frequency lead to a higher screening efficiency, but also higher wall stresses. In a ship loading process, particle streams with a wide size distribution provided a significant cushioning effect on particle degradation, and when the dropping height reduces, the dissipated energy by particle-particle impacts greatly reduced. For a grab unloader, particle velocities became smaller with an increase in grab close time with tangential stresses only slightly reduced within the close time range considered. An increase of rotational speed of the bottom blades of a screw unloader indicated a higher unloading efficiency. A full blast furnace top charging process model was also developed. Size segregation was observed at different stages of the charging process. This paper demonstrated that GPU-based DEM can be successfully applied to the whole granular process chain of ironmaking related industries at different scales and provide guidelines for the key issues in different processes.

Particle image velocimetry (PIV) is employed in this work to measure particle flow field in a two-dimensional fluidized bed to obtain particle velocity distribution function around a single bubble. Discrete element method (DEM) is also used to investigate particle velocity distribution at the individual particle scale. Both experimental and simulation results show that the velocity distribution of particles surrounding a single bubble can be described by tri-peak model which is a linear superposition of three Maxwellian distributions. A tri-peak distribution model based on the fluid and particle control mechanisms is theoretically derived. Three kinds of models such as tri-peak model, bi-peak model and single-peak model are proposed and compared. The error analysis shows that compared with other models, the tri-peak model can profile particle velocity distribution more accurately.

Particle mixtures with a wide range of sizes, shapes, and densities may experience significant segregation. In the hopper discharging process, segregation predominantly happens on the free surface of mixtures with size ratio

The electrostatic precipitator is widely used in many industries, such as power plants, waste incineration and glass production. The optimization of electrode and collecting plate is important for higher efficiency in electrostatic precipitator. In this work, the simulation results of electrical characteristics, particle charge, migration velocity and collection efficiency in four electrode configurations and two shaped collecting plates are presented. The results show that the distributions of the electric field and current density are different in each electrode and plate configuration. Sharpness of the discharge needle wire (NW) can simply lead to the high peak value of the electric field strength near the electrode wire surface. The concave-convex structure of the collecting plate can easily generate high current density near a corner of the BE collecting plate. The particle migration velocity and relative collection efficiency are calculated within eight different electrode-plate combinations. The BE collecting plate and needle wire electrode (BENW) configuration has the highest collection efficiency. The implication of the results in practice is discussed on this basis.