Particle Flow Research Articles

Modeling Dense Particle Flow in Multistage and Obstructed Flow Receivers Using High Fidelity Simulations

Particles are a leading contender for next-generation, concentrating solar power technologies, and the design of the particle receiver is critical to minimize the levelized cost of electricity. Falling particle receivers (FPRs) are a viable receiver concept, but many new designs feature complex particle obstructions that include dense discrete phase flows. This creates additional challenges for modeling as particle-to-particle interactions (i.e., collisions) and particle drag become more complex. To improve upon existing modeling strategies, a CFD-DEM simulation capability was created by coupling two independent codes: Sierra/Fuego and LAMMPS. A suitable receiver model was then defined using a traditional continuum-based model for the air and a granular model for the particle curtain. A sensitivity study was executed using this model to determine the relevance of different granular model inputs on important quantities of interest in obstructed flow FPRs: the particle velocity and curtain opacity. The study showed that the granular model inputs had little effect on the particle velocity magnitude and curtain opacity after an obstruction.

Numerical characterization on fracture evolution behavior of pre-flawed sandstone under monotonic and multilevel cyclic loading

This study employed an improved stress corrosion model within a three-dimensional particle flow program to investigate the mechanical and cracking behavior of fractured sandstone samples with varying rock bridge angles under both monotonic loading and multilevel cyclic loading. Firstly, using the experimental results from intact sandstone under uniaxial compression, we calibrated the microscopic mechanical parameters of the parallel bond model. Then, the model was validated using the experimental results of fractured sandstone under monotonic and cyclic loading. Finally, the initiation, propagation, and coalescence behavior of cracks in fractured sandstone samples under the above two loading paths, as well as the evolution process of the stress field, displacement field, and force chain distribution, were discussed in detail. The results show that the stress–strain curves, strength, deformation parameters, and macroscopic failure modes obtained from numerical simulations are consistent with those from laboratory mechanical tests. The mechanical behavior of fractured sandstone is influenced by both the rock bridge angle and the loading path. As the rock bridge angle decreases, the mechanical parameters of the sample show an increasing trend, and the influence of rock bridge angle on the failure mode is reduced. Cracks in the samples all initiate at the tips of pre-existing flaws, and the rock bridge angle affects the crack propagation and coalescence process: for sandstones with smaller rock bridge angles, cracks gradually extend to the sample’s ends; for sandstones with larger rock bridge angles, direct coalescence of cracks at the rock bridge is observed, then extending to the sample’s ends. Compared with monotonic loading, the damage degree of sandstone samples under multilevel cyclic loading is more severe, and even obvious block spalling is observed. The experimental and numerical simulation results are expected to improve the understanding of the mechanical behavior and fracture behavior of fractured rocks under monotonic and multilevel cyclic loading.

Response of a Coral Reef Sand Foundation Densified through the Dynamic Compaction Method

Dynamic compaction is a method of ground reinforcement that uses the huge impact energy of a free-falling hammer to compact the soil. This study presents a DC method for strengthening coral reef foundations in the reclamation area of remote sea islands. Pilot tests were performed to obtain the design parameters before official DC operation. The standard penetration test (SPT), shallow plate-load test (PLT), and deformation investigation were conducted in two improvement regions (A1 and A2) with varying tamping energies. During the deformation test, the depth of the tamping crater for the first two points’ tamping and the third full tamping was observed at two distinct sites. The allowable ground bearing capacity at two disparate field sites was at least 360 kPa. The reinforcement depths were 3.5 and 3.2 m in the A1 and A2 zones, respectively. The DC process was numerically analyzed by the two-dimensional particle flow code, PFC2D. It indicated that the reinforcement effect and effective reinforcement depth were consistent with the field data. The coral sand particles at the bottom of the crater were primarily broken down in the initial stage, and the particle-crushing zone gradually developed toward both sides of the crater. The force chain developed similarly at the three tamping energies (800, 1500, and 2000 kJ), and the impact stress wave propagated along the sand particles primarily in the vertical direction.

Experimental visualization of optical spatial sensitivity through combination of diffuse correlation spectroscopy and acoustic radiation force

In field of diffuse optics for biomedical applications, the spatial sensitivity (SS) is a key parameter to evaluate or optimize the adopted modalities, such as penetration depth, signal-to-noise ratio as well as sensor distribution. Nevertheless, SS is usually estimated via computer simulations (e.g., photon Monte Carlo simulation), rather than being quantified experimentally, due to the technical difficulty. In this study, we report the experimental measurement and visualization of optical SS through combination of acoustic radiation force (ARF) and the scanning diffuse correlation spectroscopy (DCS). By spatially varying the location of ARF focal spot within liquid phantom, the enhanced particle flow, which represents the most spatial sensitive location, was identified by DCS. The experimental outcomes were cross-validated with the photon Monte Carlo simulation, thus demonstrating its accuracy, feasibility, and potential for guiding clinical usage.

Hydrodynamic study of gas–liquid-solid mini-fluidization based on fluorescence PIV

The fluorescence-based tracer particle image velocimetry (fluorescence PIV) was used to obtain the flow regimes transition, bubble size and velocity, liquid and particle flow field characteristics of the 1 ∼ 3 mm GLSMFBs and 93 ∼ 195 μm glass beads. When the bed-to-particle diameter ratio increased, the bubble size and velocity distribution tended to be more concentrated. Bubble rose as straight line and S-shaped spiral trajectory. The divergence and vorticity of the flow field were preliminarily quantified. There showed a close relationship between the macroscopic hydromechanical behaviors such as bubble size and velocity and the mesoscopic behaviors such as the movement and development of vortices. The upward drag force of liquid and bubble on particles mainly affected the particle axial velocity, while the particle radial motion was mainly caused by bubble wake and surface force among particles. The results provide theoretical reference for the design and optimization of GLSMFB reactors.

A Study on the Motion Behavior of Metallic Contaminant Particles in Transformer Insulation Oil under Multiphysical Fields.

When using transformer insulation oil as a liquid dielectric, the oil is easily polluted by the solid particles generated in the operation of the transformer, and these metallic impurity particles have a significant impact on the insulation performance inside the power transformer. The force of the metal particles suspended in the flow insulation oil is multidimensional, which will lead to a change in the movement characteristics of the metal particles. Based on this, this study explored the motion rules of suspended metallic impurity particles in mobile insulating oil in different electric field environments and the influencing factors. A multiphysical field model of the solid-liquid two-phase flow of single-particle metallic impurity particles in mobile insulating oil was constructed using the dynamic analysis method, and the particles' motion characteristics in the oil in different electric field environments were simulated. The motion characteristics of metallic impurity particles under conditions of different particle sizes, oil flow velocities, and insulation oil qualities and influencing factors were analyzed to provide theoretical support for the detection of impurity particles in transformer insulation oil and enable accurate estimations of the location of equipment faults. Our results show that there are obvious differences in the trajectory of metallic impurity particles under different electric field distributions. The particles will move towards the region of high field intensity under an electric field, and the metallic impurity particles will not collide with the electrode under an AC field. When the electric field intensity and particle size increase, the trajectory of the metallic impurity particles between electrodes becomes denser, and the number of collisions between particles and electrodes and the motion speed both increase. Under the condition of a higher oil flow velocity, the number of collisions between metal particles and electrodes is reduced, which reduces the possibility of particle agglomeration. When the temperature of the insulation oil changes and the quality deteriorates, its dynamic viscosity changes. With a decrease in the dynamic viscosity of the insulation oil, the movement of the metallic impurity particles between the electrodes becomes denser, the collision times between the particles and electrodes increase, and the maximum motion speed of the particles increases.

Granule efficiency evaluation process using two-way CFD-DEM coupling analysis

Amino acid granulation using a fluidized bed is an important process that can improve the fluidity of powders and provide better process control. In this study, a granulation process evaluation procedure using numerical analysis is presented. Before analyzing the flow and particle behavior during the process, experiments and analyses such as pour angle of repose, drained angle of repose, and static angle of repose were performed to measure material properties and ensure the reliability of the numerical model. Material properties determined through experiments and numerical analyses were applied to an evaluation model of the granulation process. The granulation process is characterized by the interdependent behavior of a strong flow and large amounts of powder inside the equipment. A Computational Fluid Dynamics (CFD)-Discrete Element Model (DEM) coupled numerical model was presented for simulating particle and multiphase flow phenomena. Additionally, because there is a strong correlation between particle behavior and flow, a two-way coupling model was applied.The particle behavior characteristics are directly related to the granulation efficiency. Particle behavior was analyzed by setting four process conditions depending on the flow intensity. In this study, the concept of a dead zone was introduced to evaluate the kinetic performance of the particles under different process conditions. A dead zone is an area where the particles do not move actively and are unable to mix. The creation and size of the dead zone were compared based on the process conditions. Additionally, this study presents a procedure to evaluate the mass, volume, and size increase due to the granulation process based on the time spent in the granulation region. The granulation region is defined as the area in which the granulation of the particles is expected to proceed using the material sprayed from the nozzle. The granule quantity and uniformity were evaluated according to the process conditions. The granule amount refers to the mass and volume of individual particles that increase during the granulation process, and uniformity refers to the variation in granule amount between particles. The process efficiency can be evaluated as good when the granule amount of the work particles reaches the target value and is evenly distributed. Although the behavioral characteristics of the analyzed process did not represent all similar processes, it was confirmed that separate process conditions should be set according to the initial size distribution of the particles, target granule amount, and uniformity. Consequently, a series of processes was organized to obtain the properties of the target particles, effectively simulate the behavior inside the equipment, and reasonably determine the granulation region. Additionally, it presents a method to evaluate the amount and uniformity of granules rather than simply evaluating the time spent in the granulation region.

Simulation study on heat and mass transfer characteristics within tubular moving bed heat exchangers

In the field of waste heat recovery, tubular moving bed heat exchangers (MBHEs) hold great promise as equipment capable of effectively handling large-sized granular materials with high temperature. To further clarify the heat and mass transfer characteristics within tubular MBHEs, this study firstly conducted detailed investigations on the contributions of different heat transfer mechanisms. The result shows that heat radiation (∼45 %) and gas film heat conduction (∼42 %) control the heat transfer processes involving tube walls, with an inlet particle temperature of 600 °C, tube wall temperature of 50 °C, and particle descent velocity of 2 mm/s. These contributions can be influenced by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. Additionally, for a specific particle, its heat transfer state is highly depended on where it is located. Subsequently, the time-varying and space-varying characteristics of the heat transfer processes involving tube walls are studied. The results suggest that the time-varying and space-varying characteristics are inherent in tubular MBHEs due to the difficulty to achieve complete stability. Meanwhile, temporal fluctuations intensify with an increase in the inlet particle temperature, a decrease in wall temperature, or an increase in particle descent velocity. The result of power spectral density (PSD) indicates that the heat transfer processes exhibit a degree of chaotic behavior due to the nonlinear property of sub-models, as well as the randomness in particle feeding and contacts. The space-varying characteristic is mainly determined by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. This characteristic can be observed in both the axial and circumferential directions, with the circumferential variation being more pronounced than the axial variation. Furthermore, a double-tube MBHE, a topic that has received scant attention in previous research, is investigated in comparison to a single-tube MBHE to explore the differences in heat and mass transfer between the two configurations. It indicates that under the same boundary conditions, there are differences in heat transfer results, which are attributed to the interactions between two vertically arranged tubes. These interactions are reflected in the reconstruction of particle flow patterns and the effect altering the temperature distribution for the particles or fluid surrounding the tubes. The obtained results provide valuable insights into the mass and heat transfer behaviors of particles and fluids within tubular MBHEs, laying a foundation for advancing the development of efficient tubular MBHEs.

Extending the CFD-DEM coupling algorithm to accurately predict the particle separation in a two-phase air–solid particle flow through an aerofall AG mill

Extending the CFD-DEM coupling algorithm to accurately predict the particle separation in a two-phase air–solid particle flow through an aerofall AG mill

Investigation of the mechanical behaviour of frozen fissured sandstone addressing the role of fissure ice

Due to the existence of ice in rock fissures and the complex ice–rock interactions, the exact role of fissure ice in altering the mechanical behaviour of frozen rock mass remains unclear. In this study a series of uniaxial compression experiments were conducted on frozen sandstone samples that bearing precut fissures of different angles at both freezing and room temperatures. The failure process of samples was recorded using a high-speed camera. Besides, a particle flow code-based simulation, addressing the role of fissure ice, was performed. The results indicate that: (1) Freezing does not alter the trend of strength variation concerning the fissure angle, but it does strengthen the samples significantly. (2) At both room and subzero temperatures, the crack initiation mode of the specimens showed a changing trend of "tensile cracking → shear cracking → tensile cracking" as the fissure angle increased. (3) The change in fissure angle leads to a change in the stress state at the fracture end, while the fissure ice, through ice–rock interaction, further alters the fracture's stress state, thereby affecting the initiation and expansion mode of the fracture. Based on the simulation results, three strengthening mechanisms of fissure ice are proposed: (I) under compression, the ice acts as a filling support; (II) the fissure ice shortens the fracture length, resulting in a reduction of the stress intensity factor at the fracture ends; (III) under tensile or shear states, the ice acts as a binder. The above strengthening effects of fissure ice act simultaneously or alternatively at different fissure angles.

Modelling of particle flow code geotechnical material parameter relationships based on orthogonal design and back propagation neural network

Modelling of particle flow code geotechnical material parameter relationships based on orthogonal design and back propagation neural network

Numerical prediction on frictional characteristics of binary mixtures consisting of flexible cylindrical particles and rigid spheres

A Discrete Element Method (DEM) model for deformable cylindrical particles is established to investigate the Jenike shear process of binary mixtures consisting of flexible cylindrical particles and rigid spheres. The effects of the shape of flexible cylindrical particles and the proportion of cylindrical particles to spherical ones on the friction behavior of the mixture are discussed. Numerical results show that both the shear stress and internal friction angle increase with the aspect ratio (Ar) of the flexible cylindrical particles but decrease with the increase of the proportion of spherical particles. The role of Ar becomes slight when when the amount of spheres are much higher than the cylindrical particles (double or higher). For the mono-system containing flexible cylindrical particles of Ar=6 but without spheres, the strong interlocking packing structure leads to high shear stress and internal friction angle. It is indicated that the inclusion of rigid spheres disrupts the interlocking structure between flexible cylindrical particles and acts as a lubricant during the shear process. Based on the numerical results, a predictive correlation is established to predict the frictional characteristics of binary mixtures consisting of flexible cylindrical particles and rigid spheres considering the effect of particle shape and proportion. Furthermore, through a microscopic analysis of the numerical results, a deeper understanding of this phenomenon is gained. It is confirmed that the spherical particles can fill the voids between the flexible cylindrical particles, increasing the compactness of the mixture and promoting lubrication effects. The current research contributes to the better understanding of the mechanism of particle flow and is of paramount importance to improve the kinetic theories for complex granular flows.

On the effect of deformation conditions on the metal flow behavior during upsetting process using finite element simulation DEFORM 3D software

AbstractThe study reports on the metal flow behaviour during upsetting or forging using the finite element method. Forging simulation studied the metal flow behaviour of a laboratory-sized specimen and a cylindrical engine connecting rod specimen of AISI 52100 high-chromium steel specified in the software database. The focus was to study the effect of deformation conditions (temperature and die velocity) on metal flow behaviour during forging. The simulation results showed heterogeneous metal flow behaviour during forging. Hence, this indicates that effective flow stress and flow strain, particle flow velocity, effective strain rate, damage and temperature distribution exhibited inhomogeneous deformation behaviour. As the temperature increased, the forging load decreased, thus a decrease in deformation resistance. The simulation of the engine connecting rod further confirmed inhomogeneous deformation during forging. Damage coefficient results show that the crack pin end had a higher damage probability during forging. This study clearly showed that finite element simulation can predict metal flow behaviour during the forging of AISI 52100 steel. The study output provides a basis for analysing and optimising most industrial metal forming processes using a numerical simulation approach. Hence, this method is effective in predicting flow behaviour.

Contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation

The issue of electrostatic safety in liquid hydrogen systems has garnered increasing attention, especially concerning the potential threat of electrostatic explosions due to the collision-electrification phenomenon of solid oxygen particles formed after air leakage in liquid hydrogen pipelines. To delve into the contact electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen transportation, a mathematical model based on the computational fluid dynamics-discrete element method (CFD-DEM) two-phase flow dynamics has been developed. This model integrates the Hertz contact theory for describing particle collision processes and the condenser model for describing particle collision-electrification. The reliability of this model has been validated in existing literature through its ability to capture the flow characteristics of two-phase flow and the electrification characteristics of particle groups. Using density functional theory to compute the solid oxygen work function and considering the low-temperature properties of liquid hydrogen, a series of numerical studies on the flow sedimentation and electrification characteristics of solid oxygen particle-laden flows in liquid hydrogen pipelines have been conducted. The results indicate that particles carry negative charges after colliding with stainless steel pipe walls, with single charge exchange magnitudes of approximately 10−12C for particle-wall continuous collision processes and 10−14C for particle-particle collision processes, resulting in particle charge-to-mass ratios on the order of tens of μC/kg at the outlet interface. The impact of electrostatic forces on particle motion is significant and cannot be overlooked. Furthermore, the effects of velocity, particle diameter, and pipe diameter on particle charge characteristics have been thoroughly analyzed. At low flow velocities, severe particle settlement occurs, leading to increased collision frequency between particles and walls and significant charge accumulation. Increasing flow velocity can mitigate particle settlement and reduce charge levels. Changes in particle and pipe diameters have a minor impact on particle settlement but can increase single charge amounts with larger particle diameters and intensify particle charging with reduced pipe diameters due to shortened radial travel distances, leading to increased collision frequency. Our study meticulously illustrates the charge characteristics of individual particles and particle groups, providing a theoretical basis for assessing the electrostatic safety of liquid hydrogen transportation systems under extreme conditions.

Erosive wear and particle attrition in multi-stage solar particle receivers and screw conveyors: A CFD-DEM approach with machine learning and artificial neural networks

A coupled finite volume and discrete element method (CFD-DEM) numerical model is developed to unravel the fundamental mechanisms of granular transport, surface erosive wear and particle attrition in multistage solar particle receivers (MSPR) and screw conveyors (SC). Additionally, various regression-based supervised machine learning (ML) and artificial neural networks (ANN) are trained and optimized with the goal of quickly quantifying erosion and attrition thereby overcoming (a) the inherent challenges of high computational expense of CFD-DEM simulations and (b) exorbitant time required to post-process and extract DEM results. This study is the first of its kind to harness a synergistic numerical framework (CFD-DEM, ML, ANN) to unravel the fundamental mechanisms of erosion and attrition in MSPRs, non-vibrationally induced SCs, and vibrationally-induced SCs. It is found that the packing distribution, particle curtain width, and severity of particle scattering in a MSPR exhibits a subtle variation with particle diameter. In the context of SCs, the magnitudes of erosion and attrition are contingent on the particle diameter and flow operating conditions such as screw blade velocity, vibrational frequency and vibrational amplitude. Interestingly, a vibrationally-induced SC (VI-SC) exhibits superior performance in terms of low erosion and attrition unlike non-vibrationally induced SC (NVI-SC). It is found that MSPRs with 750–1000 µm particles and SCs with 750–1000 µm coupled with vibrational frequencies and vibrational amplitudes of 5 Hz and 0.007 m, respectively, are the preferred configurations due to minimum particle scattering, low erosive wear and low particle attrition. The trained and optimized ML models such as XGBoost, CatBoost, and Multilayer Perceptron (MLP) exhibit superior performance in predicting erosive wear and particle attrition on unseen DEM data, whereas the Multiple Linear Regression (MLR) and Gaussian Process Regression (GPR) ML exhibit poor performance prediction. For the first time, new information on fundamental granular flow dynamics, erosive wear and particle attrition in MSPRs and SCs is discerned. The methodology allows scientists to quickly examine material degradation for a myriad of industrial applications such as concentrated solar thermal (CST), among others.

Research on the Water Inrush Mechanism and Grouting Reinforcement of a Weathered Trough in a Submarine Tunnel

Based on the structural and geological characteristics of the F1 weathering trough of a submarine tunnel and its spatial relationship with the cavern, a simplified calculation model of the weathering trough water inrush was established, and the formation, development process and influencing factors of the water inrush channel in the water-resistant rock layer were carried out by a numerical simulation of particle flow. It shows that the integrity and stability of the critical water-resistant rock mass is the key to preventing water inrush, and the identification and positioning of the water inrush channel is the basis for the grouting reinforcement design of the weathering groove of the submarine tunnel. Based on above research results, the F1 weathering trough was blocked and reinforced by the composite grouting method, and the engineering reinforcement effect was good.

Revealing flow structures in horizontal pipe and biomass combustor using computational fluid dynamics simulation

AbstractComputational fluid dynamics (CFD) is a powerful tool to provide information on detailed turbulent flow in unit processes. For that reason, this study intends to reveal the flow structures in the horizontal pipe and biomass combustor. The simulation was aided by ANSYS Fluent employing standard ‐ model. The results show that a greater Reynolds number generates more turbulence. The pressure drop inside the pipe is also found steeper for small pipe diameters following Fanning's correlation. The fully developed flow for the laminar regime is found in locations where the ratio of entrance length to pipe diameter complies with Hagen–Poiseuille's rule. The sucking phenomenon in jet flow is also similar to the working principle of ejector. For the biomass combustor, the average combustion temperature is 356–696°C, and the maximum flame temperature is 1587–1697°C. Subsequently, air initially flows through the burner area and then moves to the outlet when enters the combustor chamber. Not so for particle flow, the particle experiences sedimentation in the burner area and then falls as it enters the combustor chamber. This study also convinces that secondary air supply can produce more circulating effects in the combustor.

Study of Plasma Flow Velocity in an Open SMOLA Screw Trap

The physics of confinement of a rotating plasma in a magnetic field with linear helical symmetry is being studied at the Institute of Nuclear Physics SB RAS on the open SMOLA trap. An indicator of the quality of confinement is the plasma flow velocity in the system. The paper describes the applied diagnostics based on the Mach probe under conditions of non-magnetized plasma, which made it possible to determine the longitudinal flow velocity in experiments. The measured longitudinal flow velocity was (0.5–5) · 106 cm/s in various operating modes of the installation. The dependence of the speed on the magnitude of the magnetic field corrugation is discussed. A reverse flow of trapped particles returning to the containment zone has been detected.

Effects of particle size and flow properties on the performance of ceramic-coated separators in Lithium-ion batteries

This study investigates the relationship between particle size and flow properties of boehmite powders and their impact on ceramic-coated separators for lithium-ion batteries, specifically exploring how these properties influence the performance of the separators. The separators coated with BH-3 powder, with larger sizes and better flow properties than BH-1 and BH-2, showed superior characteristics with the minimum deviation when measuring physical properties such as thickness and roughness. The BH-3 coated separators, with <10% shrinkage at 150 °C for 1 h, showed the highest ion conductivity (0.69 mS cm−1) and superior electrochemical properties compared to bare PE separators. These results highlight the importance of the excellent flow properties of the boehmite powders, which reduces the slurry viscosity, facilitates the formation of a uniform coating layer, and consequently enhances the performance of the separator.

Vortex formation driven by the particle flow at the interface of a phase-separated binary complex plasma under microgravity condition

Microparticles of two sizes are confined in a dc discharge in a glass tube with polarity switch in the PK-4 laboratory on board the International Space Station. Small and big particles separate from each other presumably due to the unbalance of the force under microgravity condition, forming an ellipsoidal interface. Particles close to the symmetric axis of the cylindrical glass tube are driven by a manipulation laser and a particle flow is generated. The flow velocity depends not only on the laser current but also on the configuration and location of the particle cloud. Counterintuitively, it is observed that a vortex can be formed at the interface, only if the flow velocity is below a certain critical value. Our experiments provide a great opportunity to study the new facets of vortex formation at particle-resolved level.