Flow Behavior Of Particles Research Articles

Flow behavior of polypropylene reactor powder in horizontal stirred bed reactors characterized by X-ray imaging

Horizontal stirred bed reactors (HSBRs) are widely used in the commercial production of polypropylene (PP). Despite their commercial significance, a comprehensive understanding of the flow behavior in HSBRs remains elusive, primarily due to the lack of detailed experimental data. This study investigates the influence of operating parameters on the particle flow behavior of two types of PP reactor powder in a laboratory-scale HSBR using X-ray imaging. Our results indicate that the overall flow behavior and phase holdup in the HSBR are dominated by agitation. Moreover, gas injection through the inlet points at the bottom of the HSBR results in spouting behavior, which can lead to reduced gas-solid contacting and, in extreme cases, complete bypass. Finally, the presence of liquid (in this study, isopropyl alcohol) adversely affects the flow behavior of the PP reactor powder due to liquid bridging at the contact points of particles. Powders that comprise particles with relatively small sizes and dense surface morphology are particularly prone to reduced flow behavior when exposed to liquid.

Atmospheric Bubbling Fluidized Bed Risers: Effect of Cone Angle on Fluid Dynamics and Heat Transfer

Abstract In this paper, a comparative study of fluid flow behavior and thermal characteristics of sand particles has been carried out numerically and experimentally in bubbling fluidized beds for five-cone angles of the riser wall having 0 deg, 5 deg, 10 deg, 15 deg, and 20 deg. An Eulerian model with a k–ε turbulence model is used to explore the numerical analysis, and the findings are compared to those of the experiments. For the study, the inlet air velocity is fixed at 1.5 m/s with sand particles filled up to 30 cm to maintain bubbling conditions in the risers. The results indicate that increasing the cone angle up to 10 deg while maintaining the amount of bed materials constant leads to a reduction in pressure drop. The expansion of particles along the riser is observed to decrease with the increase in the cone angle up to 10 deg. The radial solid volume fraction profile transforms to a U shape from the W-type profile as the cone angle increases up to 10 deg. Correspondingly, the solid velocity is found to have an inverted U-type and W-shaped profile for the risers. The granular temperature is also found to increase with a decrease in the solid percentage at any location. The average bed temperature, interphase, and bed-to-wall heat transfer coefficient at a location of 10 cm axial height also increase with the cone angle increase up to 10 deg. As a result, the conical riser, when designed with a greater cone angle up to 10 deg, exhibits more efficiency in terms of heat transfer characteristics. The 3D simulation results are in strong concurrence with the experimental results in all investigations.

Improved mesh-free SPH approach for loose top coal caving modeling

This study presents an innovative model in computational geotechnical engineering by improving the Smoothed Particle Hydrodynamics (SPH) method for simulating loose particle dynamics in coal caving processes. The improved model integrates an elastic-perfectly plastic constitutive model with the Drucker-Prager yield criterion and includes several improvements aimed at boosting accuracy, stability, and efficiency. These improvements include gravity loading coupled with particle damping, first-order stress field smoothing, and kernel gradient correction. A series of numerical experiments validates the effectiveness of the improved SPH model, demonstrating its capability to predict large deformations and track the evolution of the coal-rock interface in coal caving processes. Furthermore, the study analyzes the model's sensitivity to material parameters such as the angle of friction and material density, which aids in configuring the model for distinct coal mining situations. Results show that the non-cohesive elastic-perfectly plastic constitutive model can effectively simulate the flow behavior of granular particles, and the landslide simulation results are in good agreement with the experiments. The improved SPH algorithm with stress smoothing technique solves the problem of numerical noise, and the “double peak” stress distribution around the coal outlet is identified. The established SPH model offers an effective tool for understanding dynamics behaviors of loose top coal. Significantly, the model requires only five material parameters, which can be identified through standard experiments, avoiding the typically arduous process of parameter selection or calibration commonly existing in Discrete Element Method simulations.

Evaluating the impact of stirrer design on powder behaviour in capsule filling using dyed lactose as tracer

Ensuring temporal and spatial uniformity in the chamber of a capsule filling machine with vacuum drum is crucial for consistent dosing to in-row capsules. A stirrer must induce axial mixing to maintain a homogeneous powder bed and prevent accumulation in specific regions, primarily caused by the feeding system above the chamber. To achieve satisfactory filling, the performance of different stirrers was analysed using a tracer particle strategy. This contribution introduces a lactose dyeing process, preventing agglomerate formation and yielding minimal differences in powder properties. Four lactose grades, exhibiting diverse particle sizes and flow behaviours, were dyed with methylene blue. A comprehensive analysis of lactose properties, such as particle size, density, and flow behaviour, confirms minimal alterations post-dyeing. Tracers obtained through this process reveal that a spike-type stirrer induces more axial mixing compared to a wire-type stirrer. The dyed lactose tracers effectively contribute to understanding and optimising the capsule filling process.

Shear rate dependency on flowing granular biomass material

The commercialization of bioenergy has been significantly limited by various material handling issues due to the poor flowability of granular biomass materials. Addressing these issues demands a fundamental understanding of flow physics and robust models to predict the multi-regime flow behavior of biomass particles. In this study, we investigated the multi-regime flow behavior of loblolly pine chips, a widely used bioenergy feedstock, through combined experiments and simulations. A quasi-static hypoplastic model and a cross-regime Drucker–Prager (DP)-μ(I) model were utilized and validated against inclined plane flow experiments to understand the quasi-static and dense flow behavior of milled pine chips. The results show that along the inclined plane, loblolly pine chips mainly present in heap flow (varying thickness along the plane), and in plane flow (iso-thickness along the plane) only when the inclination closes to the material’s critical state internal friction angle. The results also show that the multi-regime DP-μ(I) model predicts a completely different velocity profile from the hypoplastic model. DP-μ(I) model can capture the flow behavior of pine chips in both flow regimes well but at the cost of extra parameter determination, and the shear-rate dependent rheology model can successfully capture the flow of elongated high-frictional particles. These findings advance the scientific understanding of the multi-regime flow behavior of granular biomass materials and shed light on formulating novel constitutive models to assist granular biomass handling in the bioenergy industry.

INFLUENCE OF SPRAY DISTANCE ON THE POROSITY OF Ni-BASED AMORPHOUS COATINGS: NUMERICAL SIMULATION AND EXPERIMENT

The influence of injection distance on the porosity of Ni-based amorphous coatings (AMCs) prepared with a high-velocity air fuel (HVAF) process is discussed based on a numerical analysis and experimental methods. A computational fluid dynamics model was established to demonstrate the gas flow field and behavior of particles in flight at different spraying distances during HVAF spraying. When analyzing the changes in the particle velocity and temperature, the spraying distance is less than 30 µm. The velocity and temperature changes of small particles have a significant impact, and the optimal spray distance (350 mm) for obtaining a low porosity coating is predicted. The calculation was validated experimentally by producing a Ni-based AMC with a low porosity (1.87 %) that was manufactured using the predicted HVAF optimal spraying distance.

Gas–solid flow mechanism of spherocylindrical particles with various aspect ratios in spouted bed

Spherocylindrical particles encompass elongated spherical particles, such as biomass particles utilized in thermal reactions and capsule pills in the pharmaceutical industry, along with various other particles found in industrial production processes. Understanding the flow behavior of spherocylindrical particles within a spouted bed holds significant practical importance. This study delves into investigating the fluidization characteristics of spherocylindrical particles with varying aspect ratios within a spouted bed. Key parameters studied include particle void fraction, velocity, orientation, and mixing. These were analyzed using the computational fluid dynamics–discrete element method, and the simulation model's accuracy was verified through high-speed photography experiments. The findings revealed distinct void fraction distributions at different locations within the bed. Particles in the higher-bed region exhibited larger void fractions with flatter peaks compared to those in the lower-bed region. Moreover, the correlation between particle aspect ratio and void fraction varied at different heights within the bed. Notably, there was no significant correlation observed between particle aspect ratio and particle velocity. However, the larger the particle aspect ratio/gas velocity, the better the particle mixing quality. Additionally, gas velocity and particle aspect ratio had little effect on particle orientation, but there was a tendency for particle orientation angles to hover around 45°–60° near the wall region.

Particle distributions in Lamb wave based acoustofluidics

Acoustic streaming enabled by a Lamb wave resonator (LWR) is efficient for particle trapping and enrichment in microfluidic channels. However, because Lamb waves combine the features of bulk acoustic waves and surface acoustic waves, the resulting acoustic streaming in the LWR occurs in multiple planes, and the particle flow behavior in this acoustofluidic system is largely unknown. Reported here are numerical simulations and laboratory experiments conducted to investigate the boundary conditions for particle motion inside a microvortex induced by an LWR. Upon dynamic capture, the particles’ trajectories become orbital paths within an acoustic vortex. The suspended particles encounter two distinct acoustic phenomena, i.e., the drag force resulting from acoustic streaming and the acoustic radiation force, which exert forces in various directions on the particles. When the acoustic radiation force and the fluid drag force are dominant for large and small particles in a mixed solution, respectively, the large particles reside within the vortex while the small particles remain at its periphery. Conversely, when the acoustic radiation force is dominant for both types of particles, the distribution pattern is reversed.

Real-Time Cone-Growth Model for Determination of Pharmaceutical Powder Flow Properties.

The flow properties of pellets or granules are crucial for further processing drug dosage forms. Optimal compression or filling of multiparticulate dosage forms into capsules is influenced by forces between discrete particles, which could be partially characterized by flow properties. Several techniques have been developed to examine flowability, including static and dynamic methods applying empirical studies and up-to-date chaos theory; however, the newest methods seem only to be powerful with the supplementation of empirical principles. Our experiments try to refine both the technique of analysis and the methods, by finding new, alternative ways. Our approach to the flowability measurements was to set up a dynamic time-dependent model that combined empirical observations and chaos theory on a geometrical basis, thus finding new characteristics regarding the flow properties of pellets and granules that could be relevant for drug developers. Our findings indicate that sphericity and particle size are the most significant factors influencing the flowability of pharmaceutical multiparticular preparations. Furthermore, this study confirms that integrating chaos theory and empirical observations in a time-dependent dynamic model provides a comprehensive understanding of particle flow behavior, pivotal for optimizing manufacturing processes.

In-situ study on flow and rotation behaviors of coal particles near the burner plane in an impinging entrained-flow gasifier

The flow behaviors of the coal particles during coal gasification in the entrained-flow gasifier are closely related to the stable operation of the gasifier, while it is difficult to observe the particles during the operation of the gasifier due to the influence of high-temperature environment and complex atmosphere. In this study, based on a bench-scale opposed multi-burner (OMB) coal-water slurry (CWS) entrained-flow gasifier and an advanced visualization system composed of a high-temperature endoscope and a high-speed camera, the flow and rotation behaviors of the coal particles near the burner plane are investigated. The region near the burner plane is divided into jet zone and impinging core. The particle trajectories in the two zones are tracked. The particle velocity distribution and velocity fluctuation index are calculated. The particle rotation and flame oscillation behaviors are quantified. The results show that the proportion of total particle trajectories in the impinging core is higher than that of the jet zone. The velocity of the particles is mostly distributed in the range of 0–4 m/s. The particle fluctuation index in the impinging core is greater than that in the jet zone, indicating that the impinging flow is more unstable in comparison with the jet flow. The particle rotation angular velocity fluctuates within a certain range, while the fluctuation range of flame oscillation angular velocity is extremely great and can be easily disturbed by the flow field. For a single particle undergoing volatile oxidation, flame oscillation and particle rotation are isotropic. The flow field near the burner plane is reconstructed based on particle flow behaviors. The reconstruction results can be applied to verify the simulation of flow field.

Process optimisation of alumina coatings by modification of powder characteristics in the aerosol deposition method

The aerosol deposition process, involving the impact of solid particles on a substrate at high velocities, is an attractive method for the manufacture of ceramic coatings at room temperature. For process optimisation, it is crucial to select a powder having the appropriate physical characteristics and evaluate the particle flow behaviour during the deposition process. In this study, a powder modification process using high-energy milling and spray drying to improve the applicability of precursor powders was developed and evaluated both numerically and experimentally. A modified aerosol deposition system incorporating a brush-type aerosol generator was employed to maintain the continuity of the aerosol supply and improve the stability of the particle concentration. The deposition efficiency was nearly tripled when using spray-dried granules (0.68%) instead of the as-received powders (0.26%). From tribological measurements, the strongest interfacial bonding was also confirmed for coatings prepared with alumina granules.

Numerical simulation of particle flow around the impulsive monopile

In order to explore the particle flow field characteristics around the impulsive monopile, the particle flow field and particle distribution around impulsive monopile were simulated based on the classical impulsive flow around a monopile at medium and low Reynolds number (Re = 550). The Large Eddy Simulation (LES) technique was harnessed to capture the dynamic flow field around the monopile and to facilitate in-depth analysis of vortex evolution. Concurrently, the Lagrangian approach was employed to track and characterize particle trajectories, shedding light on the patterns of particle diffusion and congregation in the vicinity of the monopile under varying Reynolds numbers. Additionally, this investigation unveils the distinctive behavior of particle flow during the impulsive starting and stopping phases adjacent to the monopile. Leveraging these insights, the study elucidates the intricate influence of the unsteady flow field dynamics around the monopile on the progression of particle flow.

Numerical analysis of gas-liquid-solid erosion characteristics of the oil and gas multiphase pump

In the process of oil and natural gas production, solid particle erosion is an important reason affecting the safe operation of oil and gas multiphase pumps. To reduce equipment failure rates, it is urgent to predict positions that are vulnerable to erosion damage. However, the erosion regularities of oil and gas multiphase pumps have rarely been studied in the past. In this paper, the Euler-Lagrange method is used to analyze the gas-liquid-solid flow phenomena in oil and gas multiphase pumps under different operating conditions, combined with the Oka model for erosion prediction. The validity of the erosion prediction method is verified using numerical simulation results of erosion at 90° elbows. To explore the erosion mechanism between fluid and entrained particle flow behavior, the relationship between particle parameters and erosion position and regularities is emphatically studied. The research results indicate that in a certain range, the maximum erosion rate of the oil and gas multiphase pump decreases with the increase of particle density, but increases linearly with the fluid velocity and is also affected by gas volume fraction and other particle parameters. In addition, the erosion usually occurs on the inlet, outlet wall, and the leading edge of the pump chamber, due to the different particle parameters, the erosion range will be slightly different. According to the particle trajectory, it is found that the leading edge of the pump chamber is the most erodible region due to the high frequency and intensity of particle impact. These results provide a reference for optimizing the structural design of the oil and gas multiphase pumps and help to predict their performance against wear.

Numerical study on material removal of a convex pattern surface interacting with non-spherical particles

A convex pattern surface is proposed and optimized to mitigate the sliding wear of bulk handling equipment caused by interaction with bulk solids. This work investigates the effectiveness of the convex pattern surface on wear reduction during interactions with non-spherical particles. Multiple representative particles, obtained through a sampling method, are reconstructed using a photogrammetry technique. Two contact parameters between particles are calibrated through shear box and drawdown tests to ensure flow behavior similar to the real material. The numerical results indicate that the convex pattern surface can effectively reduce wear compared to a plain sample when involving both spherical and non-spherical particles. For a plain sample, the wear volume remains independent of particle shapes and increases linearly with numerical revolutions. For the convex pattern surface, the wear volume demonstrates a quadratic relationship with the test revolutions as the deformation of convex elements weakens the effectiveness of the sample on wear reduction. The particle flow behavior analysis reveals that the convex pattern surface experiences the lowest wear volume when in contact with non-spherical particles. This can be attributed to the non-spherical particles sliding shorter distances and rotating with higher angular velocities on the convex pattern surface.

Comparative analysis of particle density effects on initial fluidization in gas-solid fluidized beds

Gas-solids fluidization technology is commonly used in chemical engineering processes involving high-density particles, often encountering poor defluidization phenomena. However, there is limited research examining the applicability of flow characteristics and empirical correlations established for low-density, easily fluidizable particles in guiding the flow behavior of high-density particles. This knowledge gap poses significant challenges for designing and operating fluidized beds in relevant processes involving high-density particles. This study comprehensively evaluates the effect of particle density on hydrodynamics during the initial fluidization stage using experimental, empirical correlations and simulation methods. Results of preliminary experiments indicate that empirical correlations for predicting Umf may exhibit significant errors of high-density particles. However, the experiments face challenges in eliminating the influence of different particle size distribution. In contrast, the simulation results present a high consistency with the experiments after sensitivity analysis. Further simulation results illustrate that empirical correlations for Umf may only yield relatively accurate predictions within the narrow density range. As the particle density increases, the predicted errors tend to increase. During the initial fluidization stage, three distinct fluidization stages can be observed, as revealed by both experiments and simulations. These stages can be attributed to the practical particle size distribution. Furthermore, it is noted that as the particle density increases, the fluidization performance tends to deteriorate. This study endeavors to advance the understanding of the effect of particle density on hydrodynamics during the initial fluidization stage. Nonetheless, more studies are still needed to enhance and deepen the current knowledge of the fluidization of high-density particles.

Calibration and verification of DEM parameters for particles in transfer chute from rapid flow to stable accumulation

The discrete element method (DEM) is conducive to optimizing bulk material conveying equipment. Calibration experiments are essential in DEM simulation, requiring particles to accurately replicate the flow behavior from rapid motion (up to a maximum of 6 m/s) to stable accumulation in bulk material handling. In typical calibration experiments, excessively high particle velocities will affect the stability of the characterization data in stable accumulation. The paper presents an innovative calibration approach that enables reliable prediction of both impact forces during rapid flow and bulk density during stable accumulation. A single-factor numerical test determines the sensitivity of simulation parameters to calibration experiments, and comprehensive testing methods ensure that equivalent DEM contact parameters align with experimental particle behavior. Finally, verification experiments indicate that the proposed calibration experiments in this study can successfully replicate the particle flow behavior during bulk material handling.

Enhancement of emulsion stability and functional properties of hemp protein‐based dairy alternative by different treatments after cellulase hydrolysis

SummaryHemp milk is a plant‐based beverage emerging as a sustainable dairy alternative and it is essential to improve the emulsification properties and stability of hemp protein for increasing acceptability. This study demonstrates the preparation of protein‐rich hemp milk with enhanced emulsion stability and functional properties through cellulase hydrolysis of fibre components in hemp protein. The emulsions were prepared using the hemp dispersions obtained after cellulase treatment followed by mechanical treatment (ME) and in combination with either enzymatic (trypsin) (EE) or mild chemical (pH‐shift) treatment (PE). The influences of these treatments on the particle size distribution, zeta potential, flow behaviour, microstructure, flocculation, and coalescence properties of the emulsions are investigated. The emulsions (EE/PE) prepared with dispersions processed through tryptic or pH shift treatments showed improved stability as indicated by reduced flocculation and coalescence indices (8.9% and 10.8%, for EE and 11.8% and 13.2% for PE) as compared to only mechanically treated emulsion (ME) (37.5% and 15.3%). Furthermore, the enhanced stability of EE and PE samples is attributed to a reduction in particle size and enhanced zeta potential (EE: 45.1 mV > PE: 38.7 mV > ME: 34.1 mV).

Wetting characteristic and flow behavior of silicate binder at various sand particle-particle interfaces: Fine or coarse, circular or angular particles

This study presents an innovative investigation into the wetting characteristic and flow behavior of sand particles, which have different shapes, sizes, and textures, when they bonded with silicate binder. The results revealed that the apparent contact angles of fine and angular particles with the binder are higher than those of coarse and circular particles. In addition, after modifying the four systems with anionic surfactants, the equilibrium contact angles decreased by 42.8%, 26.7%, 26.5%, and 7%. These findings suggest that coarse and circular particles demonstrate stronger wetting properties with the binder compared to fine and angled particles. Additionally, the cohesion and internal friction angle of the wet sand mixture can be measured through the ring shear test. Moreover, the unconfined yield strength and main consolidation stress can be calculated using the Mohr Coulomb model to obtain the yield locus and quantify the flowability of the wet sand mixture. The yield trajectory of sand mixtures at specific consolidation stresses suggests that the most important factor affecting the flowability of wet sand particles is particle size distribution. Wet mixtures of coarse and circular particles exhibit lower cohesive forces, indicating higher fluidity.

Numerical investigation of the particle flow behaviors in a fluidized-bed drum by CFD-DEM

The fluidized-bed drum technology involving the combination of a fluidized bed and a rotating drum is used for the granulation and coating of particles, which has been successfully applied in industry. Nevertheless, there should be few published fundamental studies for exploring the particle flow behaviors in a fluidized-bed drum, particularly in the particle level. Consequently, the particle-scale DEM (Discrete Element Method) was coupled with CFD (Computational Fluid Dynamics) in this work to simulate the particle-fluid flow system in a fluidized-bed drum. The experiments in a small horizontal fluidized-bed drum were also carried out to validate the accuracy of our CFD-DEM model. Subsequently, the particle flows in a large inclined fluidized-bed drum were simulated by CFD-DEM, and the relatively comprehensive investigation for the influences of operational conditions (including the gas inlet velocity, drum rotation speed, drum inclination angle and fluidized-bed inclination angle) on the particle flow behaviors (e.g., the particle holdup, particle velocity and particle residence time) was carried out. According to the simulation results, the particle flow behaviors would be significantly affected by these operational conditions. However, increasing the gas inlet velocity could weaken the effects of drum rotation speed, drum inclination angle and fluidized-bed inclination angle.

Study of atypical particle flow and free surface evolution behaviour in stirred tanks

Stirred tanks are ideal vessels for material mixing reactions in the chemical sector. However, insufficient data on the complex contact collisions occurring inside these vessels hinder their appropriate design and utilization. This study employs a coupled discrete element method and volume of fluid method (DEM-VOF) to examine the evolutionary behaviour of atypical particle flow and free surface in stirred tanks. DEM is utilized to trace particle motion and interactions, while VOF is used to capture the phase interface between the gas and liquid phases. Simulations are conducted on three commonly used particle shapes-oblate ellipsoid, sphere, and prolate ellipsoid-varying their aspect ratios under the same volume of particles. The key results of the suspension, distribution, multiphase flow, and free surface behaviours in the stirred tanks were analysed. The results show that the suspension and distribution of the three particle shapes are not substantially different, with suspension stability primarily influenced. Notably, the suspension of oblate ellipsoid particles exhibits conspicuous fluctuations. Additionally, the particle shape influences the magnitude of turbulent kinetic energy in the paddle area, with oblate particles exhibiting the largest values and prolate ellipsoids the smallest values. The findings provide guidelines for designing and operating stirred tanks under optimal conditions.