Non-spherical Particles Research Articles

Side-by-Side Testing of Grit Separation Units

Two grit removal systems were tested side-by-side for the treatment of wastewater from a combined-sewer system. The two units were operated at constant flows and variable grit loads ranging from 1.2 to 745 Kg/m3 /h that covered the typical range of dry and wet weather conditions experienced at the treatment facility. The average mass grit removal for the multi-tray free vortex unit was 92.6% and it was 85.4% for the forced vortex system. Both units consistently failed to remove particles with sand equivalent sizes, which their respective overflow rates would otherwise predict. This observation can be explained by uneven force distributions over non-spherical grit particles with lumpy grease deposits and variable curvature that effect motion traverse to flow, increase buoyancy and cause particle lift.

General aerosol Sauter mean diameter measurement for spherical and non-spherical particles based on low-complexity scattering algorithm

Sauter mean diameter (SMD) is a key microphysical indicator in aerosol measurements that rely on optical-scattering-related methods. However, owing to the lacking clear definition of non-spherical SMD and the complexity of scattering calculations for non-spherical particles, existing SMD measurement methods are only applicable to spherical particles. A general SMD measurement method for both spherical and non-spherical aerosols is thus proposed. In this method, the shape coefficients of non-spherical particles are defined and used to calculate SMD. The scattering models for spherical and non-spherical particles are unified into a low-complexity scattering algorithm (LCSA). Based on LCSA, SMD can be measured using only two light sources of different wavelengths. Compared with SMD measurement results without considering particle shape, the accuracy of the proposed method increased by an average of 11.31% and 11.37% for unimodal and bimodal aerosols, respectively, while its accuracies for spherical and non-spherical aerosols respectively reached 95.26% and 93.43%.

A database of the raindrop scattering properties at millimeter and sub-millimeter wavelengths

Currently, the majority of publicly raindrop scattering database are calculated with spherical particles. However, as the raindrop grows, the bottom of the raindrop gradually flattens out. The differences of raindrop shape will lead to a difference of the calculated scattering parameters from reality, and further influencing the accuracy of calculations in the fields of radar detection, microwave transmission and satellite remote sensing. In this regard, we developed a non-spherical raindrop scattering parameter database (RP database) with frequencies from 3GHz to 1000GHz. It has been published in an open-access repository. We compared the RP database with the database of Ekelund et al., and found that their difference is basically under 5%; Further the comparisons were also made between the scattering parameters of ellipsoids, spherical raindrops and the non-spherical raindrops, both spherical and ellipsoidal particles have clear difference from non-spherical particles. Finally, we analyzed the group particle attenuation at different frequencies.

An experimental investigation on the settling of disk particles in annular region: Wall effect and drag coefficient

Settling non-spherical and spherical particles in the annular region is common in many industrial applications. This work shows the intensification of the performance of settling particles in an annular channel by reducing the drag coefficient. The disk/cylinder particles settle in annular channels filled with Newtonian and non-Newtonian fluids. An aqueous solution of different concentrations of glycerin and Carboxymethylcellulose (CMC) was considered as the Newtonian and non-Newtonian fluids. The experimental results reported in the present work covered the 0.17 ≤ blockage ratio ≤0.55, 0.14 ≤ k (flow consistency index) ≤1.81 (Pa.sn), 0.64 ≤ n (flow behavior index) ≤1, and annular channel Reynolds number 0.40 ≤ Re ≤63.44 and 0.05 ≤ Re ≤43.02 in Newtonian and non-Newtonian fluids respectively. The wall factor, f, was increased with the increase in Re and the decrease in blockage ratio. At higher Reynolds numbers (Re), the particle’s wall factor was only influenced by the blockage ratio. The wall factor was reduced due to the particle’s shape change from cylinder to disk, i.e., decreasing the particle’s sphericity. The wall factor of particles is observed to be higher in non-Newtonian than in Newtonian fluids. The critical Reynolds number (Rec ) decreased with the H/d (Height/diameter of disk) ratio and sphericity of the studied particles. Both the drag coefficients, in the absence ( C D ∞ ) and presence ( C D ) of the wall effect, declined with the Reynolds number. Suitable correlations were developed for CD with low values of RMSLD (root mean square logarithmic deviation). The experimentally obtained drag coefficient data were also analyzed successfully using the laminar model available in Ansys (Fluent) −18.1. The computed velocity contours analyzed the wall effect and CD variations successfully. The use of the annular channel as a drag reduction device is encouraged due to the observed higher wall factor and decreased drag coefficient for particle settling in comparison to the non-annular channel.

Dynamic Light Scattering and Its Application to Control Nanoparticle Aggregation in Colloidal Systems: A Review.

Colloidal systems and their control play an essential role in daily human activities, but several drawbacks lead to an avoidance of their extensive application in some more productive areas. Some roadblocks are a lack of knowledge regarding how to influence and address colloidal forces, as well as a lack of practical devices to understand these systems. This review focuses on applying dynamic light scattering (DLS) as a powerful tool for monitoring and characterizing nanoparticle aggregation dynamics. We started by outlining the core ideas behind DLS and how it may be used to examine colloidal particle size distribution and aggregation dynamics; then, in the last section, we included the options to control aggregation in the chemically processed toner. In addition, we pinpointed knowledge gaps and difficulties that obstruct the use of DLS in real-world situations. Although widely used, DLS has limits when dealing with complicated systems, including combinations of nanoparticles, high concentrations, and non-spherical particles. We discussed these issues and offered possible solutions and the incorporation of supplementary characterization approaches. Finally, we emphasized how critical it is to close the gap between fundamental studies of nanoparticle aggregation and their translation into real-world applications, recognizing challenges in colloidal science.

Transportation and deposition of oval and cylindrical shaped proppant particles in complex-fracture systems

Hydraulic fracturing treatment can create complex fractures to provide oil and natural gas flow path. To achieve a high conductivity, the proppant should be placed properly in the fractures. Up to date, nearly all proppant materials used are spherical or nearly spherical particles and the effect of proppant shape is rarely reported. In this work, we investigate the flow, transport and deposition of non-spherical proppant particles in complex fractures. The results show that in the primary fracture, the packing patterns of ovals behave as spheres, but cylinders show a significant difference. Ovals can enter subsidiary fractures at a lower pump rate than cylinders and spheres. The effect of fluid viscosity on the packing pattern is also examined, revealing a significant influence in the primary fracture, but not much in the subsidiary fracture. The proppant transportation efficiency decreases with increasing the fluid viscosity for the conditions considered in this work.

Ignition characteristics of the high-velocity pulverized coal jet in MILD combustion mode: Experiments and prediction improvements

The influence of high jet velocity on the ignition characteristics of pulverized coal is very important for the Moderate or Intense Low-oxygen Dilution (MILD) combustion technology of pulverized coal. This paper conducts experimental and numerical simulation research on the ignition characteristics of the pulverized coal jet in a high-temperature environment based on the Hencken-type flat flame burner. The results show that when the ambient temperature is 1873 K and the ambient oxygen mole fraction is 5 %, the ignition delay distance of the pulverized coal jet decreases as the jet velocity increases from 15 m/s to 100 m/s for the formation of MILD combustion. The adoption of the turbulent particle heat transfer model and the non-spherical particle motion model effectively improves the prediction of particle dispersion, ignition delay, and reaction zone in the high-velocity coal jet flame. The enhancement of gas–solid heat transfer by turbulent fluctuation plays a dominant role in advancing the coal ignition in the high-velocity jet, while the non-spherical shape of coal particles mainly improves the uniformity of reaction distribution. The influence of ignition characteristics in the high-velocity jet on the MILD combustion formation of pulverized coal has been also analyzed in detail.

The study of equilibrium dynamics of the collinear restricted four-body problem with non-spherical test particle

In the present manuscript, the dynamics of the non-spherical test particle in the planar version of spatial collinear restricted four-body problem is presented. Using the numerical methods, the parametric variation of the position of libration points (LPs) is illustrated when the oblateness/prolateness parameters vary in the pre-assumed intervals. Moreover, it is also unveiled how these parameters affect the stability of the LPs and the regions of motion. For all the LPs, we have shown their nature by classifying them not only in two category i.e., as linearly stable and unstable but also as minima, index-1, and index-2 saddles. The performed numerical investigations strongly suggest that the oblateness/prolateness parameters are indeed very influential factors in this dynamical model.

Effect of fluid inertial torque on the rotational and orientational dynamics of tiny spheroidal particles in turbulent channel flow

Rotation and orientation of non-spherical particles in a fluid flow depend on the hydrodynamic torque they experience. However, little is known about the effect of the fluid inertial torque on the dynamics of tiny inertial spheroids in turbulent channel flows, as only Jeffery torque has been considered in previous studies by point-particle direct numerical simulations. In this study, we investigate the rotation and orientation of tiny spheroids with both fluid inertial torque and Jeffery torque in a turbulent channel flow. By comparing with the case in the absence of fluid inertial torque, we find that the rotational and orientational dynamics of spheroids is significantly affected by the fluid inertial torque when the Stokes number, which is non-dimensionalized by fluid viscous time scale, is larger than the critical value $St_c\approx 2$ , indicating that the fluid inertial torque is non-negligible for most particle cases considered in earlier studies. In contrast to the earlier findings considering only Jeffery torque (Challabotla et al., J. Fluid Mech., vol. 776, 2015, p. R2), we find that prolate (oblate) spheroids with a large Stokes number tend to tumble (spin) in the streamwise–wall-normal plane in a thinner region near the wall due to the presence of the fluid inertial torque. Approaching the channel centre, the flow shear gradually vanishes, but the velocity difference between local fluid and particles is still pronounced and increasing as particle inertia grows. As a result, in the core region, fluid inertial torque is dominant and drives the particles to align with its broad side normal to the streamwise direction rather than a random orientation observed in earlier studies without fluid inertial torque. Meanwhile, the presence of fluid inertial torque enhances the tumbling rates of spheroids in the core region. In addition, the effect of fluid inertial force on the dynamics of spheroids is also examined in this study, but the results indicate the effect of fluid inertial force is weak. Our findings imply the importance of fluid inertial torque in modelling the dynamics of inertial non-spherical particles in turbulent channel flows.

Formation and morphological evolution investigation of the porous silicon decorated with Pt particles

Platinum nanoparticles were prepared on silicon substrates at room temperature using electroless deposition with different durations from 1 to 40 min. The effect of deposition times on the morphology and composition of the deposited Pt particles and porous films was examined using scanning, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering. Moreover, atomic force microscopy was used to examine the structural properties and morphological characterization of the deposed particles. The wetting properties of the por-Si/Pt structure were investigated using the sessile drop method. The research indicates that the por-Si/Pt structure has uniformly distributed nonspherical self-assembled Pt particles with a height of up to 120 nm and a diameter of 200 nm. The concentration of these particles is 2.5 × 109 cm−2 and there is a mesoporous silicon layer with a thickness up to 580 nm. A uniform size distribution of the particles is achieved after 1 min of deposition. The conditions for creating the por-Si/Pt structure, characterized by a high Pt particle concentration and coverage, have been identified. The morphology parameters of the particles and layers depend on the duration of the deposition. The evolution of the formation of an array of platinum particles, meso- and macroporous silicon, including all stages of growth of the components of the Por-Si/Pt structure was established.

Study of polarization transmission characteristics in nonspherical media

In order to deal with the problem of serious pollution caused by non-spherical particles, this study developed and obtained a non-spherical medium based on the theoretical basis of polarized optics and a new non-spherical particle preparation method (burning Ganoderma lucidum spores method). A polarized light simulation transport model based on the T-matrix was established by applying it to the smoke simulation environment. Using this polarization transmission model, simulation experiments were conducted to determine the effects of wavelength, polarization state, optical thickness and various transmission media on the Degree of Polarization (DOP). The simulation results show that both incoming linearly and circularly polarized light undergo depolarization as the optical thickness increases; however, the depolarization of circularly polarized light becomes more severe. In addition, the DOP in the non-spherical particle medium is always larger than that in the spherical particle medium, which indicates that the circularly polarized light is superior to the linearly polarized light in terms of deflection precession.

Super-quadric CFD-DEM-VOF modelling of gas–solid-liquid systems

In many chemical engineering processes, gas–solid-liquid flow involving nonspherical solid particles is commonly practised and should be modelled for process understanding and optimisation; however, reliable modelling along with parallelization is still lacking. This work combines an unresolved CFD-DEM-VOF coupling framework, featuring a super-quadric particle shape model to model the gas-nonspherical particle-liquid flow and a “ghost domain” algorithm to improve the parallelization efficiency. The model is applied to two cases – cuboid particle sedimentation and dambreak formation, for model effectiveness demonstration. According to the simulation results, the model effectively captures the interactions between particles and phases in the relevant scenarios. This is reflected by the agreements of numerical simulations and experimental or analytical data in these two cases. Moreover, the parallelization technique utilizing the “ghost domain” displays remarkable steadiness and noteworthy efficiency. As the processor number increases from 2, 4, 8, 16, to 32, the running time obviously decreases almost linearly. This research introduces an innovative computational approach for simulating systems containing gas, non-spherical particles, and liquid. It demonstrates the method’s potential to analyze interactions between particles and fluids in the unresolved framework.

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.

Cr3+ substitution effect on Co-Cu and Cu-Co nano ferrites on structural and morphological properties

The Cr3+ substituted Co-Cu (Co0.7Cu0.3Fe2-xCrxO4) and Cu-Co (Cu0.7Co0.3Fe2-xCrxO4) where x = 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25 nano ferrite composite were prepared with the sol-gel approach. Their structural, dc electrical resistivity, and magnetic properties were analyzed. XRD shows the single-phase spinel ferrite. Adding Cr3+ ions decreases the lattice volume and the size of the crystallite respectively. FESEM images show non-spherical particles on a largely uniform surface shape with decreasing grain size on doping Cr3+. The FTIR pattern supports the XRD patterns for spinel ferrite.

Rigid clumps in the MercuryDPM particle dynamics code

Discrete particle simulations have become the standard in science and industrial applications exploring the properties of particulate systems. Most of such simulations rely on the concept of interacting spherical particles to describe the properties of particulates, although, the correct representation of the nonspherical particle shape is crucial for a number of applications. In this work we describe the implementation of clumps, i.e. assemblies of rigidly connected spherical particles, which can approximate given nonspherical shapes, within the MercuryDPM particle dynamics code. MercuryDPM contact detection algorithm is particularly efficient for polydisperse particle systems, which is essential for multilevel clumps approximating complex surfaces. We employ the existing open-source CLUMP library to generate clump particles. We detail the pre-processing tools providing necessary initial data, as well as the necessary adjustments of the algorithms of contact detection, collision/migration and numerical time integration. The capabilities of our implementation are illustrated for a variety of examples.

Morphological and chemical characterisation of indoor quasi-ultrafine particles

Particles in the nanoscale range have intrinsic physicochemical characteristics that define their interaction with the human body and ultimately their toxicity. Whilst research has focused on engineered nanomaterials or ambient ultrafine particles, little is known about the morphology, size and elemental composition of particles in the nanoscale range collected in indoor environments, where humans spend the longest time. This study aims to characterise the physicochemical properties of quasi-ultrafine particles (qUFP), with an aerodynamic diameter <250 nm, collected with a Sioutas impactor from 5 indoor environments (3 homes and 2 offices). Morphology, size and elemental composition of individual particles were imaged using a Transmission Electron Microscope coupled with X-ray energy dispersive spectroscopy. Most of the single particles and their aggregates were of irregular shapes, and some fibrous rods, elongated rods, spheres and hexagons were also observed. ImageJ software was used to analyse the surface area, roundness and circularity of the particles, as well as individual particle diameter for the spherical particles. For the non-spherical shaped particle, the particles were manually measured to characterise the maximum Feret diameter. Particle main dimensions (i.e. diameter for spheroids and maximum Feret diameter for irregular particles) ranged from 35 ± 59 nm to 103 ± 160 nm. Shapes for non-spherical particles were assigned by visual description. Si, Fe and S were found in nanoparticles from all indoor locations. Other abundant constituents were K, Cr, Na, Ca, Cl found in 60–80% of locations. Minor constituents of indoor nanoparticles were Cu, Sn, Ti, Mo, Al, P, Be, F, Zn, Rb, Pb, Mn and Co. Sources were related to indoor emissions, e.g. printers, stainless-steel tools, electronics, cooking, house chores, particle re-suspension, aerosol and cleaning products as well as to penetration of outdoor nanoparticles from vehicular emissions, soil and secondary aerosols. Detailed investigation of the physicochemical properties of these particles can help understand their associated hazard and their fate in the human body.

Oblique impact breakage unification of nonspherical particles using discrete element method

Particle breakage commonly occurs during processing of particulate materials, but a mechanistic model of particle impact breakage is not fully established. This article presents oblique impact breakage characteristics of nonspherical particles using discrete element method (DEM) simulations. Three different particle shapes, i.e. spherical, cuboidal and cylindrical, are investigated. Constituent spheres are agglomerated with bridging bonds to model the breakage characteristics under impact conditions. The effect of agglomerate shapes on the breakage pattern, damage ratio, and fragment size distribution is fully investigated. By using a newly proposed oblique impact model, unified breakage master surfaces are theoretically constructed for all the particle shapes under oblique impact conditions. The developed approach can be applied to modelling particulate processes where nonspherical particles and oblique impact breakage are prevailing.

Lorenz-Mie theory-type solution for light scattering by spheroids with small-to-large size parameters and aspect ratios.

There has been a long-term endeavor in the light-scattering research community to develop a Lorenz-Mie theory-type method for simulating light scattering by spheroidal particles with small-to-large sizes. A spheroid is a very important nonspherical shape in modeling the optical properties of many natural particles. For the first time, we develop a computationally feasible separation of variables method (SVM) in spheroidal coordinates to compute optical properties of spheroids with small-to-large sizes compared to the wavelength of the incident light (λ). The method is applicable to spheroids with size parameters (2π/λ times the major semiaxis) up to at least 600, and is not restricted by particle aspect ratios. Therefore, the work reported here represents a breakthrough in solving the optical properties of a nonspherical particle in an analytical form.

Experimental investigation of the behavior of non-spherical particles in a small-scale gas-solid fluidized bed

The present work examined the effect of particle shape on the fluidization behavior at different inlet superficial gas velocities. The experiments are performed in a laboratory-scale 3D circular fluidized bed column of 1 m height and 0.067 m inner diameter with Geldart D particles of four different shapes. The effect of particle shape on pressure drop, bed expansion, and solids holdup are analyzed. Non-spherical particles have lower minimum fluidization velocities and higher bed expansion than spherical particles. The shape of particles significantly impacts the solids holdup, and it has been observed that spherical particles exhibit a higher solids holdup at the same superficial velocity. The time series analysis of the pressure signals is investigated by the frequency domain method using the Fast Fourier Transform (FFT). The FFT is implemented in Matlab R2021b to obtain the Power Spectral Density (PSD). The analysis of the PSD pattern shows the flow regime transition with the change in the particle shape. PSD pattern has observed a broad range of frequencies between 1 and 5 Hz. The dominant frequency of around 3 Hz corresponds to the bubbles or slugs that pass the bed.

Использование метода дискретных элементов для имитационного моделирования выемки угля очистным комбайном

Timulation modeling as a method of studying complex technological processes is successfully used in mining. Due to the creation of digital models, it is possible to estimate and improve the efficiency of technical and organizational solutions used in difficult mining and geological conditions. The article describes the development of a simulation model of coal extraction by a shearer and its transportation to an armored conveyer. Fragmentation of a high coal seam was simulated under the action of the cutting planes of the shearer. The created model in the Rocky DEM simulation environment takes into account the physical and mechanical properties of materials and 3D structures of mining equipment. The method of discrete elements was used as a mathematical tool for computing fragmentation of the coalbed, which helped to perform the computing without loss of the initial mass and volume of the materials. During the validation of the simulation model, a series of tests were carried out to determine the angle of natural slope of non-spherical coal particles close in granulometric composition to the mass formed during the fragmentation of the coalbed. Based on the test results, an array of values of coal particle adhesion parameters was obtained, which allows conducting simulation studies in conditions of existing and projected coal mines.