Mono-sized Particles Research Articles

Effects of the inclusion shape, arrangement, and volume fraction on effective elastic moduli of two-dimensional two-phase composites

The spatial arrangement and shape of inclusions can have a major impact on two-phase composites' mechanical properties. Few studies consider the coupling effects of these two factors on the effective elastic moduli of two-phase composites. This study introduces the circularity of inclusions to modify the three-point approximation (TPA) for quantitatively predicting the coupling effects of inclusion planar arrangement and shape. Two-dimensional particle packing structures of monosized particles are generated with polygons, superellipses, and superovals of different circularities and volume fractions via the ordered arrangement approach or the discrete element method. Then, the lattice model is conducted on the particle packing structures to verify the reliability of the modified TPA. The comparison between the theoretical calculation and the numerical simulation indicates that our modified TPA can predict the effects of planar arrangement, shape, and volume fraction of inclusions on the effective moduli. The proposed modified TPA offers fresh perspectives on comprehending intricate relationships between the macro-property and composition of composites.

The influencing factors and mechanisms of granular flow dynamics

This study proposes an approach that combines experimental and numerical simulations to comprehensively elucidate the factors influencing the physical behaviour of granular flows. The rotating drum experiments are used to investigate the behaviour of mono-sized and poly-sized particle systems under increasing rotational speed of the drum. The experimental data is then integrated with GPU-based DEM simulations. This allows for the inverse calibration of key parameters like dynamic friction and damping ratios. These calibrated parameters are subsequently utilized throughout the study to explore the influence of various factors on granular flow dynamics. The increase in RPM leads to a rise in particle dispersion due to the interplay between centrifugal forces and particle collisions. The higher dynamic friction angles result in a steeper angle of repose and consequently shorter and longer runout distances for both mono-sized and poly-sized particles respectively. Conversely, increasing damping ratios lead to a decrease in the angle of repose and promote a well-organised flow patterns with increased frictional resistance, suggesting a significant impact on overall flow dynamics. The study paves the way for new insights into the behaviour of complex particulate systems, potentially benefiting various fields concerned with granular flow phenomena.

Effect of Grinding Media Grading on Liner Wear and Load Behavior in a Ball Mill by Using Rocky DEM

The liner is a wear-prone component in ball mills, subject to continuous impacts, squeezing, and abrasion from the grinding media during operation. Its service performance directly affects the working efficiency of the ball mill. The service life of mining ball mill liners is about 8 months, and frequent downtimes occur due to liner wear and loss of effectiveness, with liner replacement accounting for about 6% of the total cost, resulting in huge economic losses. This paper focuses on a Φ305 mm × 150 mm experimental ball mill, using the discrete element software Rocky Discrete Element Method (DEM) (software version number Rocky 2022 R2) for simulation modeling analysis. With Φ10 mm and Φ20 mm mono-size particle simulations serving as reference groups, this study investigates the motion states and liner abrasion patterns under different liner heights for both sizes of grinding media in Equilibrium Quality Manufacturer (EQM) and Original Equipment Manufacturer (OEM) gradations. The results indicate that the impact of liner height on the wear of the ball mill liners is related to the size and gradation of the grinding media. The degree of liner wear from highest to lowest is as follows: EQM > Φ20 mm > OEM > Φ10 mm. Due to the effect of the cylinder end cap, the wear at the axial center of the ball mill liner is more severe than at both ends, and the wear on the facing side of the liner is more severe than on the backside. A thorough study of the influence of ball mill grinding media gradation on the wear pattern of liners is of great theoretical significance for optimizing liner structures, improving grinding efficiency, and promoting energy saving and cost reduction in ball mills. This study provides theoretical guidance for understanding the mechanisms behind liner wear in ball mills and predicting the liner lifespan.

Preparation of mono-sized high sphericity Al-Si alloy particles for thermal energy storage materials by pulsated orifice ejection method

The demand for Al-Si particles with high sphericity and narrow size distribution is growing in the field of thermal energy storage. In this study, a novel pulsated orifice ejection method (POEM) was successfully employed to produce different-sized Al-Si alloy particles. The analysis indicates that such particles exhibit high sphericity, with each particle having a sphericity exceeding 0.9. The particles are precisely size-controllable and mono-sized, thereby ensuring that they have the identical thermal history. The combination of cooling rate calculation and particle structure analysis indicates that the particles prepared by POEM exhibit higher cooling rates through rapid solidification, resulting in finer and more uniform microstructures. The thermal analysis results demonstrate that the Al-Si alloy particles prepared in this study have high melting latent heat (approximately 500.87 J/g) and solidification latent heat (approximately 467.26 J/g), showcasing their potential as high-efficiency phase change materials for high-temperature thermal energy storage.

Hydrodynamics of a Multisized Particle Mixture in Shallow Fluidized Bed With Immersed Tubes

Abstract Inert solid particles have made the integration of more efficient power cycles with super high operating temperatures into the concentrated solar power (CSP) station feasible. Fluidized bed heat exchangers with feature of high heat transfer coefficient have great application potential in the particle-based CSP. However, the parasitic loads of the additional fluidizing gas loop and the finely sieved monosized particles may deteriorate the economic efficiency of the integrated system. In order to cope with this problem, a conceptual design of a shallow fluidized bed (SFB) heat exchanger is proposed for the new generation CSP technology. Fluidization characteristics of bauxite particles with a nonuniform particle size distribution in SFB with immersed tubes are investigated with a combination of experimental measurements and computational fluid dynamics simulations. Results show that the static bed height and opening area ratio of the distributor has insignificant influence on the range of semifluidized region and the minimum fluidization velocity Umf. The standard deviation of bed pressure drop σ in the grid region can be used as an alternative criterion for identifying the fluidization state. A range of superficial velocity that distinguishes two different solid circulation patterns exists, with its boundary values being four times and eight times the Umf, respectively. The immersed tubes can inhibit the asymmetric particle circulation patterns from developing in the SFB, but cause a substantial increase in the σ within the grid region.

Particle size and shape effect of Crumbler® rotary shear-milled granular woody biomass on the performance of Acrison® screw feeder: A computational and experimental investigation

Physical experiments and discrete element model (DEM) simulations are conducted to evaluate particle characteristics and operation parameter effects on screw feeding performance for rotary shear-milled Douglas fir. Three performance metrics are used: mass flow rate, shaft driving torque, and specific energy consumption. The impact of particle size, particle size distribution (PSD), shaft rotational speed (rpm), and hopper dimensions on the performance are investigated. All employed performance metrics reveal the superior flowability of the 2-mm particles in contrast to the larger 6-mm counterpart. Remarkably, wider PSD results in poorer flowability than the two mono-sized particles, proving the flowability enhancement achieved by narrower PSD of the woody feedstock. More importantly, DEM simulations unveil PSD-induced degradation in flowability is attributed to mechanical interlocking and particle segregation effects. Furthermore, higher shaft rpm causes higher mass flow rate at the cost of higher specific energy consumption due to viscous dissipation and changes in flow pattern.

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

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

Synthetical designing of solid oxide fuel cell electrodes: Effect of particle size and volume fraction

Solid oxide fuel cell (SOFC) electrode microstructures composed of catalyst, electrolyte and pore phases with various microstructural features are synthetically generated and the effects of the mean particle size and volume fraction of each phase on three/triple phase boundaries (TPBs) are computed. For mono-sized particles with an equal volume fraction, the active and total TPB density are found to decrease with increasing the mean particle size due to decreased surface area. However, both are found to be inversely related to the square of the mean particle size. Active TPB densities of 37.62 μm μm−3, 9.27 μm μm−3 and 4.11 μm μm−3 are obtained from the electrode microstructures with mono-sized particles of 0.25 μm, 0.50 μm and 0.75 μm mean particle size, respectively. Moreover, ∼94% of the total TPB density is determined to be active regardless of the mean particle size. TPBs for the polydisperse particles with the same volume fraction also show a decreasing trend with the mean particle size in general. However, no significant change is observed in inactive TPB formations even for the largest particle size investigated, revealing almost fully percolated phases can be achieved when the volume fraction of each phase is equal (∼33.3%). On the other, when the volume fractions are also varied, the active TPB is shown to be strongly depended on the volume fraction of the phase having the highest mean particle size. In this regard, among the related cases studied, the lowest active TPB density is computed as 0.25 μm μm−3, whereas the highest one is measured as 26.64 μm μm−3.

Wet mono-sized granular packing: effects of initial clusters and filling strategy

Cohesive particles have been demonstrated to affect packing structures that sometimes inhibit applications while helpful in others. Therefore, accurately tailoring the cohesive granular packing, e.g., wet particles, is very rewarding nowadays. We adopt the discrete element method (DEM) and present a packing strategy by falling different size clusters containing mono-sized particles with varying cohesion to tailor the packing structure. We demonstrate the strategy's effectiveness by comparing the result with previous experiments, and we found the larger cluster tends to form a looser packing. We evidence that a dimensionless number, l⁎, evaluating the competing importance between kinetic energy and capillary potential, can precisely describe the cohesion effect. We combine l⁎ with several key indices, e.g., packing fraction, granular temperature, coordination number and force network distribution, to describe packing formation. Meantime, we found the different characterisation of cohesion effect throughout packing stages, which can shed light on the understanding of wet granular packing.

CFD-DEM numerical study on air impacted packing densification of equiaxed cylindrical particles

A CFD-DEM model was developed to reproduce the packing densification process of mono-sized equiaxed cylindrical particles under air impact. The effects of operating parameters on packing density were firstly studied. Then various microscopic properties of packing structures such as coordination number (CN), contact types, particle orientations, pore features were characterized and compared. And corresponding densification mechanisms were analysed based on particle motion behaviour, local structure evolution, and forces. Results indicate that the air impact can realize the packing densification of cylindrical particles under appropriate conditions. The pore size distribution in the packing of cylindrical particles shows a tail at larger pore sizes compared with that in the packing of equal spheres. Both the size and the sphericity of the pores decrease in the final dense packing; also, more surface-surface and less surface-edge contacts between two particles therein can be formed. More cylindrical particles tend to be in parallel or perpendicular contact with each other to form more stable local structures during air impact. Most particles at higher position move down (direction of gravity/air impact) with about one particle length during the densification process and most particles exhibit translational motion to realize the local rearrangement for pore filling through air impact induced inter-particle forces.

Modeling particle-particle binary coagulation rate constants for spherical aerosol particles at high volume fractions using Langevin Dynamics simulations

Effect of volume-fraction and particle-particle hydrodynamic interactions on the coagulation rate of particles are investigated. Particle coagulation is modeled using Langevin Dynamics (LD) based trajectory simulations of N mono-sized spherical particles in a periodic domain. The extended Kirkwood-Risemann approach (J. Fluid Mechanics 855, 535 (2018)) is invoked to compute particle-particle hydrodynamic interactions whose effect is parameterized as a function of the momentum Knudsen number (Kn). The results are summarized as a model for coagulation rate constant (βij) that depends on the diffusive Knudsen number (KnD) used in prior work to parameterize coagulation in the dilute regime (Aerosol Sci. Tech. 45, 1499 (2011)), Kn and particle volume-fraction ηv. In the absence of hydrodynamic interactions, it is observed that the coagulation rate constant in the continuum limit for mass transfer (KnD→0) is significantly enhanced by a factor of ∼80 at ηv∼0.3 due to particle crowding. While considering hydrodynamic interactions for ηv≥0.05, we use a screening distance around each particle that scales inversely with ηv beyond which the contribution of farther neighbors is neglected owing to the rapid decay of hydrodynamic interactions with distance. We also present new LD calculations of βij and elucidate the dependence of the same on Kn1 and the particle radii ratio θr for the coagulation of two particles in the dilute limit ηv→0. It is observed that the reduction of βij becomes significant as Kn1→0: at the lowest momentum Knudsen number considered (Kn1=0.1): βij is reduced by a factor of ∼10 for equally sized particles (θr=0.5). At high KnD,Kn1, the particle size disparity is not significant, and it is seen that βij matches hard sphere predictions, indicating the insignificant contributions by hydrodynamic interactions. A series of animations of 2-particle simulations are presented as part of the Supplemental Information to illustrate the role of hydrodynamic interactions in particle coagulation. Computational results are summarized as regressions for convenient incorporation into particle/droplet growth sectional models.

Impact of Mono- and Dual-Sized α-Fe2O3 Catalyst Mixtures on the Thermochemical Processing of Pinewood for Upgraded Liquid Chemicals

The incorporation of mono-sized particle catalysts in real industrial systems for biomass conversion is a significant challenge, hence the impact of individual α-Fe2O3 catalysts with varying non-ideal spherical sizes of 54 nm (FS054), 221 nm (FS221), and ∼2 µm (FSm002) as well as dual-sized mixtures (FS054-FS221 and FS221-FSm002) were considered in the catalytic upgrading of pinewood pyrolysis vapors. The size variation of the α-Fe2O3 catalyst revealed a substantial effect on the product distribution. Although the yield of phenols shows a decrease by almost a factor of two irrespective of the catalyst particle size, the FS221 catalyst demonstrates the most potent effect on reducing phenols through decarboxylation reactions. Considering the role of the catalyst on the individual phenolics, the FS221 catalyst reveals higher selectivity towards the reduction of 2-methoxyphenol, isoeugenol, and eugenol, whereas the application of FS054 catalysts displays a stronger impact on the decrease of creosol and other phenols. Both FS054 and FS221 catalysts showed the highest effectiveness in reducing the relative yield of 2-methoxy-4-vinylphenol. Applying a dual-size mixture (FS054-FS221) shows a synergetic effect, simultaneously decreasing the content of phenols, acids, and aldehydes followed by a strong CO2 release attributed to competitive decarbonylation reactions of aldehydes. The appearance of γ-Fe2O3 small fraction was revealed in the powders with mono-(FS221) and dual particle size (FS054-FS221 and FS221-FSm002), whereas the FS054 and FSm002 catalysts demonstrate good chemical and phase stability.

Bulk densities and flowability of non-spherical particles with mono-sized and particle size distributions

The angle of repose, angle of tilting, and Hausner ratio are frequently used to estimate the flowability of particulate materials. In addition, free and tapped densities are commonly used for the design and operation of systems for handling particulate solids. In this study, these properties were determined for mono-sized and particle size distributions of three non-spherical particle materials. Based on previous and additional new measurements with new size fractions of mono-sized particles, it was found that mono-sized properties can be described as simple new functions (replacing the previous correlations) of the Archimedes number. Mixtures with wider size distributions were defined using logistic functions based on the median size and distribution parameter. Normalizing the measured property by the median size and assuming it to be mono-sized enabled finding a simple relation to the distribution parameter, equivalent to that found for spherical particles. Thus, the appropriate properties can be predicted based on the size distribution.

Investigation of granular capillary rising under vertical vibration

The phenomenon of granular capillary rising under vertical vibration provides a novel technical route for hoisting, transporting and collecting granular materials. However, there are still obvious deficiencies in the existing studies of the granular capillary rising behavior, especially the intensive investigation on the effects of gravitational acceleration, horizontal vibration component and particle size distribution are still lacking. To address these problems, the discrete element method is used to numerically simulate the granular capillary rising phenomenon under different operating conditions. The final capillary rising height and average capillary rising velocity of the granular matter are computed and analyzed based on the numerical simulations. The results show that the granular capillarity can also occur under low gravity conditions, and that the final capillary rising height and the average capillary rising velocity first increase and then decrease with the gravitational acceleration. It is also found that the final capillary rising height is insensitive to the variation of horizontal vibrational component, whereas the average capillary rising velocity increases with the augmentation of horizontal vibrational component. Compared with the mono-sized particles, the particles with the same mean size but having a Gaussian size distribution exhibit a maximal capillary rising height at a larger critical tube diameter. Meanwhile, the average capillary rising velocity of the particles having a Gaussian size distribution is faster in the tube diameter range where the granular capillary dynamics for both size distributions is dominated by the jamming effect.

Analysis of flow behavior of cohesive monosized spherical and non-spherical particles in screw feeder

Screw feeders are extensively used in agriculture and processing industries to transport bulk material at relatively controlled rate. The flow behavior can be affected by present moisture content as well as by shape and size of particles which tend to cause bridging or arching of material. In this work, the cohesion between mono-sized spherical particles (due to moisture content), is simulated parametrically by means of cohesion energy density parameter. The correlation acts as an additional normal force to Hertz elastic theory to maintain the contact between two particles. Further, the work is extended by comparing the flow behavior of spherical with non-spherical particles by introducing the non-sphericity (cylindrical shape) using superquadric approach. The superquadric DEM simulation has shown good agreement with our experimental studies for model validation. The simulations quantify the screw feeder performance in terms of average particle speeds (radial, swirl and axial) and contact forces (normal and tangential) by varying screw rotational speed, flight pitch ratio and particle feedrate. The average radial and swirl speeds have shown opposite variation for bigger particle size with increasing cohesion energy density for all three varying conditions. The contact forces between particles also increases with increasing cohesion energy density. The quantitative results depict the same behavior for non-spherical particles as for spherical particles, but with lower magnitude for average particle speed as well as for contact forces.

Dissolution kinetics of marmatite in sulfuric acid-ferric sulfate‑sodium chloride‑oxygen media at atmospheric pressure

An experimental investigation was carried out to improve the zinc dissolution rate in the direct atmospheric leaching of marmatite by adding sodium chloride to the sulfuric acid-ferric sulfate‑oxygen media. The experiments were carried out by using mono-sized marmatite particles varying the concentrations of sulfuric acid from 0.1 to 1.3 M, ferric sulfate from 0 to 0.8 M, sodium chloride from 0 to 1.3 M, and temperature in the range of 60 to 95 °C. The results showed that the addition of 0.7 M of sodium chloride improved drastically the direct leaching kinetics of the zinc sulfide; therefore, this leaching media is an excellent alternative to produce zinc from marmatite concentrates at ambient pressure. The sulfuric acid concentration was also found to have a significant effect on the rate of dissolution, indicating that the non-oxidative dissolution of marmatite plays an important role in the reaction mechanism in this system. A shrinking core model with diffusion through a product layer control was found to fit the reaction rate. An apparent activation energy value of 81.8 kJ/mol was found for the temperature range of 60–95 °C. The direct atmospheric leaching of marmatite in H2SO4-Fe(SO4)1.5-NaCl-O2 is an excellent alternative method to extract zinc due to high dissolution rates obtained in the presence of chloride ions, reducing substantially the treatment times.

Investigation of the flocculation and sedimentation of TiO2 nanoparticles in different alcoholic environments through turbidity measurements

Turbidimeters are low-cost devices, which are widely used for suspended sediment monitoring (SSM). The specific turbidity is typically relative to 1/d (d is the diameter of particles) regarding the suspensions with mono-sized sphere-shaped particles. As the production of the dispersed suspension of TiO2-NPs is vital for their photocatalysis applications, turbidity provides a test to measure the dispersion of TiO2-NPs. In the present paper, the performance of a self-manufactured turbidimeter device has been investigated using the suspensions of TiO2-NPs in different alcoholic media. The results showed that over time, the intensity of light passing through the upper part of the test tube containing TiO2-NPs suspension increased, suggesting the settlement of TiO2 nanoparticles. In the middle part of the test tube; however, an almost stable trend was observed, which was more evident in the case of isopropanol with higher viscosity. The results also illustrated that there was no relation between the concentration of suspension and the value of transmitted light for concentration below 0.08 g/l; however, for concentrations above that, the intensity of transmitted light decreased with the increase of suspension concentration.

DEM simulations of vibrated sphere packings in slender prismatic containers

Discrete Element Method (DEM) simulations are carried out to investigate the packing structure of the vibrated mono-sized and polydisperse particle assemblies in slender prismatic containers. Quantities like void fraction distributions, coordination number distribution, Voronoi packing fraction distributions were analyzed. DEM simulations show excellent agreement with the experimental data. The transient response of the packing structure during the vibration of mono-sized spheres reveals that the crystallization starts at the walls. The packing structure's crystallinity enhances during vibration, increasing the packing density of the assembly. Vertical vibration is found to be more effective compared to lateral vibration. The packing structure is found to be independent of the container's orientation during the filling process. The influence of the ratio of the container dimensions to mean particle diameter (X/dm) and polydispersity (λ) on the packing structure is analyzed. The results showed that the increase of X/dm ratio or λ, increases the random arrangement of particles.

Effect of particle size distribution on Acoustic Doppler Velocimeter backscatter for suspended sediment measurements

The capability of acoustic Doppler velocimeters (ADVs) to estimate suspended sediment concentration has been widely investigated using glass microspheres of the same size or well-sorted fractions in experimental studies. Sediment mixtures in the natural environment may have various types of grain size distribution. This study aims to investigate experimentally the acoustic response to probability distributions in suspension including quite coarse sediment fractions up to a diameter of 300 μm. Modification of scattering and attenuation characteristics by introducing a size distribution is evaluated using the formulations given in the literature. In laboratory experiments, three different types of sediment size distributions constituting a wide size range of non-cohesive quartz sediments, namely uni-modal mass distribution, bi-modal mass distribution, and uniform number distribution, were generated. Acoustic backscatter measurements were made by immersing the ADV in a circulation tank filled with mixtures of sediments with known concentration and particle size distribution. Acoustic estimates of suspended sediment parameters obtained for different particle size distributions are compared with those for mono-size particle suspensions to show the effect of introducing a size distribution in suspension. The acoustic response from size distributions agrees with the general theoretical behavior such that the slope of the calibration curve decreases as the sediment size increases. The scattering and attenuation properties are modified compared to the mono-size suspension with the same mean size. In a region close to the geometric scattering regime, the backscattering coefficients for the particle size distributions are around 34% lower than those for mono-size particles, which results in lower backscattering strengths compared to the mono-size suspensions under the same concentration conditions. The sediment attenuation coefficient showed a smaller reduction (11%), resulting in a negligible change in the calculated signal corrected for water and sediment attenuation compared to the values for mono-size suspension of the same particle size. The information on the form of the probability distribution and the sorting of sediments in suspension is important for acoustic estimates of suspended sediment parameters. Introducing a particle size distribution affects the scattering properties more significantly than the attenuation properties for the geometric scattering regime.

Numerical study of effects of device design on drug delivery efficiency for an active dry powder inhaler

Active dry powder inhalers (DPIs) actuated by low air volume provide distinct advantages for delivering aerosols to patients with poor respiratory capacity. This work aims to investigate the effects of piercing aperture location and inlet flow rate on device-emptying, and to identify the mechanism of particle deposition in a realistic mouth-throat (MT) region. Computational fluid dynamics (CFD) is employed to predict dispersion parameters that measure turbulence intensity, and mono-sized particles are tracked by the discrete phase model (DPM). Results show that the piercing aperture location and the inlet flow rate both have significant impacts on device emptying. Strong correlations have been established between the emitted dose and flow field parameters. The pattern and distribution of the deposited particles in the realistic MT region are highly sensitive to particle size, flow rate and reservoir length. This work provides profound insights into the performance of the active DPIs and an additional perspective on device design.