Particle Aspect Ratio Research Articles

Understanding magnetic hyperthermia performance within the "Brezovich criterion": beyond the uniaxial anisotropy description.

Careful determination of the heating performance of magnetic nanoparticles under AC fields is critical for magnetic hyperthermia applications. However, most interpretations of experimental data are based on the uniaxial anisotropy approximation, which in the first instance can be correlated with the particle aspect ratio. This is to say, the intrinsic magnetocrystalline anisotropy is discarded, under the assumption that the shape contribution dominates. We show in this work that such a premise, generally valid for large field amplitudes, does not hold for describing hyperthermia experiments carried out under small field values. Specifically, given its relevance for in vivo applications, we focus our analysis on the so-called "Brezovich criterion", H·f = 4.85 × 108 A m-1 s-1. By means of a computational model, we show that the intrinsic magnetocrystalline anisotropy plays a critical role in defining the heat output, determining also the role of the shape and aspect ratio of the particles on the SLP. Our results indicate that even small deviations from spherical shape have an important impact on optimizing the heating performance. The influence of interparticle interactions on the dissipated heat is also evaluated. Our results call, therefore, for an improvement in the theoretical models used to interpret magnetic hyperthermia performance.

Drag, lift and torque correlations for axi-symmetric rod-like non-spherical particles in locally linear shear flows

This paper derives new correlations to predict the drag, lift and torque coefficients of axi-symmetric non-spherical rod-like particles for several fluid flow regimes and velocity profiles. The fluid velocity profiles considered are locally uniform flow and locally linear shear flow. The novel correlations for the drag, lift and torque coefficients depend on the particle Reynolds number Rep, the orientation of the particle with respect to the main fluid direction θ, the aspect ratio of the rod-like particle α, and the dimensionless local shear rate G̃. The effect of the linear shear flow on the hydrodynamic forces is modeled as an additional component for the resultant of forces acting on a particle in a locally uniform flow, hence the independent expressions for the drag, lift and torque coefficients of axi-symmetric particles in a locally uniform flow are also provided in this work. The data provided to fit the coefficient in the new correlation are generated using available analytical expressions in the viscous regime, and performing direct numerical simulations (DNS) of the flow past the axi-symmetric particles at finite particle Reynolds number. The DNS are performed using the direct-forcing immersed boundary method. The coefficients in the proposed drag, lift and torque correlations are determined with a high degree of accuracy, where the mean error in the prediction lies below 2% for the locally uniform flow correlations, and bwlow 1.67%, 5.35%, 6.78% for the correlation accounting for the change in the drag, lift, and torque coefficients in case of a linear shear flow, respectively. The proposed correlations for the drag, lift and torque coefficients can be used in large-scale simulations performed in the Eulerian-Lagrangian framework with locally uniform and non-uniform flows.

Quantitative Estimation and Comparative Assessment of Particle Morphological Features and Energy Requirement During Hammer Milling of Softwood Chips and Wheat Straw

Highlights Quantified particle size and shapes generated during hammer milling of softwood and wheat straw. Size reductions in length and width correlated with milling energy requirement. Assessed the validity of existing comminution laws for predicting milling energy requirement. Improved milling energy requirement prediction for softwood based on size reductions. Abstract. The valorization of agricultural and woody residues into higher quality fuels is an attractive pathway and can contribute to decarbonizing the energy system. One essential step for the conversion of these residues to fuels is comminution through commercial mills. This study aimed to investigate the effects of feedstock, input feed size, and milling screen size on particle size and shape, as well as to validate the reliability of existing comminution laws for predicting energy requirements during hammer milling of agricultural and wood biomass. Additionally, the study proposed a new empirical correlation for comminution energy prediction, taking two-dimensional size reduction descriptors into consideration. A machine vision-based image processing method was used to estimate particle size, particle size distribution (PSD), and particle shape factors. The aspect ratio of wheat straw particles was 1.3 to 1.5 times larger than softwood particles, suggesting they are more fibrous. The shapes generated during hammer milling were estimated, with rectangular shapes being predominant. The specific energy requirement (SER) estimated for the hammer milling of softwood chips and wheat straw at different mill screen sizes (4, 8, and 12 mm) was found to be in the range of 153.2–25.5 kJ kg-1 and 38.5–16.1 kJ kg-1, respectively. The validity of existing comminution laws to predict the SER during hammer milling of softwood and wheat straw was tested at a fixed feed rate of 45 kg hr-1, and an improvement in SER prediction for softwood was achieved by formulating a new empirical correlation factoring size reductions in length and width. Further, the correlation developed for the SER for wheat straw was found to lack statistical significance. The findings of this study can be applied to improve the effectiveness of the comminution process, a critical precursor to numerous thermochemical conversion methods used for transforming biomass residues into valuable fuels. Keywords: Bioenergy, Biomass comminution, Machine-vision image analysis, Particle shape, Particle size distribution, Specific energy consumption.

Super-quadric CFD-DEM study of spout deflection behaviour of non-spherical particles in a spout fluidized bed

Non-spherical particles are commonly encountered in chemical engineering processes including fluidization processes, yet their instability phenomena still lack understanding. In this study, the spout deflection – a typical instability phenomenon of non-spherical particles in a pseudo-two-dimensional (pseudo-2D) spout fluidized bed is first studied by a super-quadric computational fluid dynamics-discrete element method (super-quadric CFD-DEM) model. The intensity of spout deflection is quantified by the spout deflection angle concept. The effect of particle shape (i.e., sphere, cubic, ellipsoid, and cylinder) on the flow in terms of flow pattern, spout deflection, pressure drop, particle orientation, and normal contact force is systematically studied and compared by the time- and frequency-domain analysis. It shows that the spout channel becomes narrower for cubic, ellipsoid and cylinder particles where the particle aspect ratio increases. With the increase of spouting gas velocity, the median value of the spout deflection angle decreases and increases for cubic and ellipsoid particles, respectively. Furthermore, the pressure drops in the vertical and horizontal directions of the cubic, ellipsoid, and cylinder particles are different from each other. At last, In the bed of cubic particles, the ordered arrangements appear close to the wall region and random arrangements occur in the other regions. This work reveals the influences of non-spherical particles on spout deflection and offers insights into practical applications through optimal operation.

Collisions among elongated settling particles: The twofold role of turbulence

We study the collision rates of settling spheres and elongated spheroids in homogeneous, isotropic turbulence by means of direct numerical simulations aiming to understand microscale-particle encounters in oceans and lakes. We explore a range of aspect ratios and sizes relevant to the dynamics of plankton and microplastics in water environments. The results presented here confirm that collision rates between elongated particles in a quiescent fluid are more frequent than those among spherical particles in turbulence due to oblique settling. We also demonstrate that turbulence generally enhances collisions among elongated particles as compared to those expected for a random distribution of the same particles settling in a quiescent fluid, although we also find a decrease in collision rates in turbulence for particles of the highest density and moderate aspect ratios (A=5). The increase in the collision rate due to turbulence is found to quickly decrease with aspect ratio, reach a minimum for aspect ratios approximately equal to 5, and then slowly increase again, with an increase up to 50% for the largest aspect ratios investigated. This non-monotonic trend is explained as the result of two competing effects: the increase in the surface area with aspect ratio (beneficial to increase encounter rates) and the alignment of nearby prolate particles in turbulence (reducing the probability of collision). Turbulence mixing is, therefore, partially balanced by rod alignment at high particle aspect ratios.

Digital Design of Crystallization Process: Why particle size and shape matters!

Populationbalance modelling is a widely used tool to understand the mechanism and kineticparameters of crystal growth at the bench, to facilitate scale-up to Production.In this work, we present recommendations for particle size and shape analyticalmethods to improve the predictive capability of 1D and 2D population balancemodels for crystallisation of contemporary active ingredients. For 1D models, wereport that the optical model for laser diffraction, a common technique formeasuring particle size distribution, can significantly impact the growth parametersresolved from the model. For 2D models, particle image analysis of powders andsingle crystals give valuable length and width data to predict how the aspectratio of particles evolves. Future work will be directed towards applying thesetools when scaling a crystallization process.

Percolation Thresholds for Spherical Aggregates: Impact of the Primary Particle Aspect Ratio

Percolation Thresholds for Spherical Aggregates: Impact of the Primary Particle Aspect Ratio

The sedimentation behaviors of elliptical active particles in a rectangular box

The “squirmer” model, a micro-swimming model driven by an imposed tangential velocity at the boundaries, is used to simulate the sedimentation behaviors of one and two elliptical active particles in a two-dimensional rectangular box. Six typical locomotion modes (including the steady vertically moving (SVM), steady inclined sliding (SIS), unilateral attracted oscillating (UAO), bilateral attracted oscillating (BAO), chaotic attracted oscillating (CAO), and up-down alternate tumbling (UAT)) are identified. The effects of particle aspect ratio (AR = 0.2∼1.0), self-propelling strength (β = −5∼5), swimming Reynolds number (Res = 0.1∼5.0), and density ratio of particle to fluid (γ = 1.01∼2.1) on the sedimentation behaviors of particles (the locomotion modes and the terminal Reynolds number (Ret)), are discussed. It is concluded that the locomotion modes are closely relevant to AR, γ, and Res. The collision between particles only changes their orientations but is not sensitive to the final locomotion modes. At Res≥4.0, the modes of puller type particles change from UAO to SIS or SIS to UAT. Meanwhile, it is found that (ⅰ) particle's Ret increases with AR when it is in SIS; a larger AR leads to a greater decay of Ret when it is in UAO; the decay of Ret is smooth when it is in BAO. (ⅱ) A large |β| results in a large Ret for a particle in SIS, and it is more prominent for a puller type particle than a pusher type particle. (ⅲ) In the falling period, Res speeds up a pair of pusher type particles, while it is more prominent for the pusher type particle with a lower initial position; Res also speeds up both neutral type particles with a linear relationship of Ret∼1.35Res. γ and Ret are linear positive correlated for both a pair of pusher type particles and a pair of neutral type particles.

Material characterisation of anodising effects on small fatigue crack nucleation in AA7XXX alloys

The precursor cleaning steps in the anodising surface finish process for aluminium alloy aircraft parts are known to lead to etching of surface-breaking intermetallic particles and grain boundaries, which in turn leads to preferential sites for fatigue crack nucleation. Type 1C anodising per MIL-A-8625F, is a favoured aircraft aluminium part corrosion protection treatment meeting modern health and environmental requirements. Type 1C anodising uses electrolysis in a non-chromic acid bath (typically based on sulphuric, boric-sulphuric or phosphoric acid formulations) to develop a thick aluminium oxide surface layer. In previous studies the equivalent initial damage sizes of these nucleation sites was calculated from near surface fatigue crack growth measurements using quantitative fractography in both Type 1C anodised aluminium alloy 7050-T7451 and 7085-T7452. A notable difference was observed in the values for these two materials with AA7085-T7452 equivalent initial damage sizes being significantly smaller. Since these values are critical crack starting size assumptions in fatigue life analysis for aircraft fleets, the observed differences must be investigated and explained for notionally similar alloys under identical conditions.In this work, the material surrounding the population of crack nucleation sites in several Type 1C anodised fatigue tested specimens manufactured from AA7050-T7451 and AA7085-T7452 materials has been characterised using precise surface preparation methods and scanning electron microscopy techniques. It has been demonstrated that there is a statistically significant difference in the number, size, aspect ratio and distribution of surface breaking Al7Cu2Fe intermetallic particles beneath the anodising layer that, when etched out during the anodising process, are responsible for fatigue crack nucleation in 7050-T7451 over 7085-T7452 material. The increased size, angular shape and coverage of these intermetallics in AA7050 serves to increase their effectiveness as preferential locations for fatigue crack nucleation through two mechanisms, as a highly localised stress concentrating feature, as well as through their ability to sample more of the material's microstructural features ensuring a discontinuity is present in the most favourable orientation and location for fatigue crack nucleation.

Preparation and Characterization of Ultrafine Nitroguanidine with Different Aspect Ratios

Preparation and Characterization of Ultrafine Nitroguanidine with Different Aspect Ratios

Rotation of a fibre in simple shear flow of a dilute polymer solution

The motion of a freely rotating prolate spheroid in a simple shear flow of a dilute polymeric solution is examined in the limit of large particle aspect ratio, $\kappa$ . A regular perturbation expansion in the polymer concentration, $c$ , a generalized reciprocal theorem, and slender body theory to represent the velocity field of a Newtonian fluid around the spheroid are used to obtain the $O(c)$ correction to the particle's orientational dynamics. The resulting dynamical system predicts a range of orientational behaviours qualitatively dependent upon $c\, De$ ( $De$ is the imposed shear rate times the polymer relaxation time) and $\kappa$ and quantitatively on $c$ . At a small but finite $c\, De$ , the particle spirals towards a limit cycle near the vorticity axis for all initial conditions. Upon increasing $\kappa$ , the limit cycle becomes smaller. Thus, ultimately the particle undergoes a periodic motion around and at a small angle from the vorticity axis. At moderate $c\, De$ , a particle starting near the flow–gradient plane departs it monotonically instead of spirally, as this plane (a limit cycle at smaller $c\, De$ ) obtains a saddle and an unstable node. The former is close to the flow direction. Upon further increasing $c\, De$ , the saddle node changes to a stable node. Therefore, depending upon the initial condition, a particle may either approach a periodic orbit near the vorticity axis or obtain a stable orientation near the flow direction. Upon further increasing $c\, De$ , the limit cycle near the vorticity axis vanishes, and the particle aligns with the flow direction for all starting orientations.

Influence of particle shape on creep and stress relaxation behaviors of granular materials based on DEM

The creep and stress relaxation behaviors stem from time-dependent changes in the microstructure of granular materials. As a non-negligible inherent granular material characteristic, particle shape plays a significant role on the formation and evolution of microstructure. However, the effects of particle shape on creep and stress relaxation behaviors of granular materials are still open questions. In this study, 3D DEM models based on the rate process theory and superellipsoids are incorporated to simulate the creep and stress relaxation of granular samples with different aspect ratios and blockiness. The results show that the aspect ratio and blockiness of particle have a great effect on creep and stress relaxation. However, the effects of aspect ratio and blockiness on creep and stress relaxation are coupled. Further analysis on contact forces shows the influences of aspect ratio and blockiness on creep mainly come from the contact force ratio. The influences of the aspect ratio and blockiness on stress relaxation mainly arise from the variation of the normal contact force anisotropy of the granular assemblies. The above results provide the tendency and mechanism on the effects of particle shape on creep and stress relaxation of granular assemblies.

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.

Micro-mechanical analysis of particle shape effect on suffusion of gap-graded soils

Suffusion refers to the process of fine particles carried away from a coarser soil matrix by seepage flow. Numerical simulations of coupled fluid–solid methods are wildly used in analyzing micro and macro behaviors of gap-graded soils during suffusion. However, the solid particles are usually simplified to spheres, resulting in inaccurate detachment, transmission and clogging mechanisms. In this study, the complex particle shape factor is taken into account in CFD–DEM. A series of numerical tests were conducted to explore the effects of aspect ratio both for fine and coarse particles. Macroscopic and microscopic information of suffusion process is obtained. Numerical results indicate that particle shape plays a significant role in suffusion.

Shape-dependent radial segregation in rotating drum: Insights from DEM simulations

This study evaluates how particle shape affects the segregation behavior of binary mixtures in a rotating drum. The Discrete Element Method (DEM) is used to investigate radial segregation and its dependence on particle shape by varying the particle’s aspect ratio. Two scenarios are examined: one when the shape of fine particles held constant and varying shape for coarse particles, and another when the shape of coarse particles held constant and varying shape for fine particles. These scenarios help quantify the relative mixing observed in the system for the considered shapes. The SI trend in terms of aspect ratio (AR) for coarse particles is as follows: AR (5.0) > AR (2.5) > AR (1). In contrast, for fine particles, the trend is AR (5.0) > AR (1) > AR (2.5). The results indicate that coarse particles with lower packing density exhibit higher segregation. Conversely, fine particles with pronounced elongation facilitate mixing.

Angle of repose for superquadric particles: Investigating the effects of shape parameters

This study develops a model for the angle of repose (AOR) of granular materials composed of non-spherical particles represented by a superquadric function featuring five distinct shape parameters. Our investigation integrates experimental and numerical analyses based on the lifting cylinder approach, using a total of 30 different particle shapes. Initially, we validate a superquadric-based discrete element method using spherical particles and two spheroidal particles, emulating m&ms and Pinto Beans. Subsequently, we examine the impact of each shape parameter on the AOR and heap geometry to identify the most influential parameters. We then construct the AOR model as a function of the particle aspect ratio defined using a combination of the shape parameters. To assess the accuracy and predictive capacity of the proposed AOR model, we conduct six blind tests involving particles with varying shapes and numbers. The results demonstrate a remarkable accuracy, with an average R2 value of 98.6%. Additionally, to showcase the practicality of the proposed AOR model, we apply it to estimate the internal friction angle and the soaked California Bearing Ratio (CBR) of dry sand samples. The results show estimation errors below one percent, underscoring the predictive accuracy and reliability of the model.

Formulating, assessing and using shear thickening fluids for cork helmet liners

In this work, an assessment of different environmentally friendly formulations for shear thickening fluids (STFs) is performed. These formulations consist of concentrated dispersions of particles of precipitated calcium carbonate (PCC) in glycerin varying mass concentrations combined with four particle aspect ratios. A full rheological characterization is developed under simple shear (steady and oscillatory tests, i.e., SAOS and LAOS) and elongational flows. The study allows not only to select the most convenient particle aspect ratio and concentration of PCC, but also to observe a clear viscoelastic behaviour that shows unexpectedly “Beads On A String” (BOAS) structures under extensional flow, which is characteristic of polymer solutions. It is reported for the very first time that a continuous shear thickening fluid exhibits an increasing relaxation time with the extension rate within the thickening region. Based on the rheological information, the best formulation was used to develop reinforced cork composites that were implemented in cork helmet liners. The impact performance of the STF-cork helmet liners was better than commercial helmet liners without hard shell and for a reduction of 36% in thickness.

Impact of particle elongation on the behavior of round and angular granular media: Consequences of particle rotation and force chain development

We developed a 2D discrete element model to simulate shearing response of elongated round and angular particles. Model was calibrated and validated by comparing numerical results with corresponding biaxial shearing tests on circular (round) and hexagonal (angular) rods at microscopic and macroscopic scales. Then, the systematic effect of particles aspect ratio was investigated on quasi-static shearing response of round and angular granular materials. Macroscopically, we observed a nonlinear tendency wherein as the aspect ratio decreased from 1, the critical state stress ratio initially increased, reaching a maximum, followed by a decreasing trend. This effect was more prominent in round samples. Microscopically, decreasing the aspect ratio from 1 reduced particle rotations and increased the mean coordination number. Elongated particles exhibited significant contact anisotropy, forming irregular force chains, facilitating interparticle sliding, and reducing overall strength. Additionally, we explored the impact of the interparticle friction coefficient. A high value of interparticle friction coefficient led to a monotonically increasing strength with elongation, underscoring the importance of accurately calibrating microscopic friction coefficients.

Non uniform micromagnetic states in spheroidal magnetite nanoparticles

Non uniform micromagnetic configurations are calculated in spheroidal magnetite nanoparticles with different semiaxis ratios, a/b = 0.5 – 2.0, using Landau-Lifshitz-Gilbert equation. We take into account a complex, combined type of particle magnetic anisotropy, associated with the presence of both cubic magneto-crystalline anisotropy and shape anisotropy of spheroidal magnetite nanoparticle. It is shown that, depending on the particle aspect ratio, there are different types of vortex states, which compete in energy with the uniform magnetization. It is also found that the single-domain diameters of magnetite nanoparticles significantly depend on the orientation of the cubic easy anisotropy axes with respect to the symmetry axis of a spheroid. The calculated single-domain diameters of spheroidal nanoparticles are in satisfactory agreement with analytical estimates.

DEM study of mixing performance of superquadric particles in an industrial-scale ribbon mixer

Horizontal ribbon mixers with a U-shaped vessel are widely used to mix non-spherical particles, yet the accurate characterisation of particle morphology and in-depth elucidation of the mixing mechanisms are still lacking. In this study, a superquadric DEM model is developed to study the mixing behaviours of non-spherical particles in an industrial U-shaped ribbon mixer. The model of superquadric particle mixing is first validated against experiments. Then the influences of two key particle shape-related parameters (i.e., aspect ratio and surface blockiness) on the mixer performance are comprehensively evaluated in terms of Lacey mixing index, velocity distribution, dispersion coefficient and force analysis. The results show a weak dependence of mixing behaviours on the variation of particle aspect ratio. The case of aspect ratio of 1.0 indicates the minimum degree of mixing, followed by the cases of aspect ratios of 0.5, 2.0 and 4.0. On the other hand, with the increase of surface blockiness from 2 to 7, the degree of mixing at the quasi-steady state decreases from 0.886 to 0.875, and the proportion of particles having larger contact forces also slightly decreases. This work provides a cost-effective tool to evaluate the superquadric particle mixing in an industrial U-shaped ribbon mixer.