Orientation Of Non-spherical Particles Research Articles

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.

Experimental and numerical study on the orientation distribution of cylindrical particles in random packed beds

Cylindrical particles are widely employed in chemical engineering when a high surface area is necessary for process intensification. However, reliable information about the orientation of non-spherical particles in random packed beds is very scarce. Moreover, a potential effect of the orientation of cylindrical particles on fluid flow has not been examined yet in a real packing geometry. In this work, a new experimental approach has been applied to perform systematic studies of global and local orientation of cylindrical particles in random packed beds. Five different column-to-particle diameter D c / D p ratios were examined, ranging from 4 to 15.1. Orientation distribution was measured in the entire bed, with the bottom region excluded and in the core zone. Next, the experimental cases were reconstructed numerically with different packing densities. Finally, the effect of different orientation distributions of cylindrical particles, including full cylinders (FC) and Raschig rings (RR), on pressure drop (for identical bulk void fraction) in a selected packed bed configuration was examined numerically through computational fluid dynamics simulations. Reproducibility of particles’ orientation distributions was found to be dependent on the number of particles per layer. A substantial effect of the column wall and its bottom on particles orientation was observed. The effect of orientation of FC on pressure drop was found to be moderate, however, in the case of RR, the maximum difference in pressure drop among investigated orientation distributions was as high as 400%. • Systematic experimental analysis of cylindrical particles’ orientation in random packed beds. • Verification of reproducibility of the orientation distribution. • Reproduction of the orientation distribution in a numerical simulation. • CFD study of pressure drop in random packed beds with respect to orientation distribution.

On the determination of 3D position and orientation of spheroidal particles using defocusing and deep learning

Tracking the 3D position of tracer particles or small objects like cells or unicellular organisms in miniaturized lab-on-a-chip or biomedical devices is complicated since it is often not possible in these setups to use multi-camera approaches. Most successful single-camera approaches for these applications are based on holography or defocusing. Holographic methods have been used to track complex objects such has bacteria (Bianchi et al. (2019)) and even to estimate their orientation (Wang et al. (2016)). However, these methods require a complex and expensive experimental setup which is not always available in research laboratories. On the other hand, defocusing methods work with conventional microscopic optics, are easy to implement, and have shown excellent results in 3D PTV experiments (Qiu et al. (2019)). One main drawback is that they normally work only with spherical and mono-dispersed tracer particles. A defocusing method that has potential to measure non-spherical particles is the General Defocusing Particle Tracking (Barnkob and Rossi (2020)) which is based on pattern recognition and can be conceptually extended to more complex tasks by extending the reference library of particle images, including not only spherical particles at different depth positions, but also non-spherical particles at different orientations. However, whether this approach could work in practice is still unknown. First, is the information contained in simple defocused images sufficient to reconstruct depth and orientation of non-spherical particles, and eventually under which circumstances? Second, how to practically collect the labelled reference images?

Method for the determination of preferential orientation of marine particles from laser diffraction measurements.

In situ laser diffractometry (LD) is increasingly used in oceanographic studies to estimate sediment transport, particle fluxes and to assess the concentration of marine phytoplankton. It enables an accurate characterization of the size distribution of suspended particles from the scattering signal produced by their interaction with a collimated laser beam. LD reliably reflects the sizes of suspensions dominated by nearly spherical particles; however, when complex particle morphologies dominate the suspension (e.g. phytoplankton) the resulting particle size distribution (PSD) may present significant variations attributed to different factors. In particular, the orientation of non-spherical particles - which abound in the sea - modifies LD measurements of PSDs. While this may be interpreted as a drawback for some studies (i.e. when precise measurement of the volume concentration is required), we propose that detailed analysis of this signal provides information on particle orientation. We use PDMS micropillars with prescribed elliptical cross-sections to experimentally determine the dependence between the spatial orientation of elongated particles and changes in the PSD measured with a LISST laser diffractometer. We show that LD can be used to adequately characterize the different dimensions of the non-spherical particles at specific orientations. Using this property, we describe and validate a method to infer the preferential orientation of particles in the sea. Our study opens new perspectives in the use of in-situ LD in ocean research.

Orientation of spheroidal particles in single jet bubbling fluidized beds

Particle shape has a significant effect on the characteristics of fluidized beds due to the anisotropy of non-spherical particles. In particular, particle shape can affect the bubble dynamics such as bubble size, shape and velocity. However, the relationship between bubble dynamics and the orientation of non-spherical particles is not clear. This paper presents a detailed analysis on orientation of spheroids in a gas-solid fluidized bed operated with a continuous central jet. Spheroids with aspect ratios at 0.5 (oblate) and 2 (prolate) are employed to represent disc-like and rod-like particles, respectively. The results show that the orientation of spheroids is directly related to bubble motion. The orientation evolves with bubble progression and prefers to align in the bed horizontally or vertically depending upon the bubble position. Further, frequency distributions of spheroids orienting parallel/perpendicular with fluid flow direction were analysed in terms of several hydrodynamic parameters such as particle position and velocity, and fluid drag force. The results indicate that spheroids have different orientations depending upon the hydrodynamic parameters. The findings obtained from this study can aid to better understand fluidization dynamics associated with non-spherical particles.

Study of drag and orientation of regular particles using stereo vision, Schlieren photography and digital image processing

A new experimental, image-based methodology suitable to track the changes in orientation of non-spherical particles and their influence on the drag coefficient as they settle in fluids is presented. Given the fact that non-spherical solids naturally develop variations in their angular orientation during the fall, none-intrusiveness of the technique of analysis is of paramount importance in order to preserve the particle/fluid interaction undisturbed. Three-dimensional quantitative data about the motion parameters is obtained through single-camera stereo vision whilst qualitative visualizations of the adjacent fluid patterns are achieved with Schlieren photography. The methodology was validated by comparing the magnitudes of the drag coefficient of a set of spherical particles at terminal velocity conditions against those estimated from drag correlations published in the literature. A noteworthy similarity was attained. During the fall of non-spherical solids, once the particle Reynolds number approximated 163 for disks, and 240 for cylinders, or exceeded those values, secondary motions composed by regular oscillations and tumbling were present. They altered the angular orientation of the particles with respect to the main motion direction and caused complete turbulent patterns in the surrounding flow, therefore affecting the instantaneous projected area, drag force, and coefficient of resistance. The impact of the changes in angular orientation onto the drag coefficient was shown graphically as a means for reinforcing existing numerical approaches, however, an explicit relation between both variables could not be observed.

Nano-Composite manufacturing using the Electro-Orientation method of Micro/Nano-Particles in a liquid polymer with mechanical characteristics analysis

A new technology for manufacturing micro/nano composites by utilizing an electric field to fabricate particle orientations in a polymer liquid state is developed and its thermo-mechanical properties are tested. This method allows the manipulation of the local orientation of the submerged micro/nano size particles in a liquid matrix. The study demonstrates that the technology is able to locally manipulate the particle orientation and applicable diverse metal/non-metal inclusions in a polymer matrix. The theoretical background of this process includes the dielectrophoresis, diploe moment, and electrophoresis of particles in a polymer matrix. Electrophoresis is an important phenomenon in the orientation of non-spherical particles in a continuous phase. Attempts were made to distribute several types of metal and non-metal particles in a liquid epoxy, in order to test the effects of electrophoresis under an electric field; the rotation and alignment of the particles were clearly observed and pictures were taken. The mathematical models of the kinetic movements caused by the electrophoretic force are also presented here. The results obtained from the experiment indicate the effectiveness of the proposed method and validate the suggested mathematical models, including all of the expanded manipulation.

Numerical investigation of mixing and orientation of non-spherical particles in a model type fluidized bed

A numerical investigation of mixing in a model type fluidized bed is performed based on the three-dimensional discrete element method coupled with computational fluid dynamics (CFD). Particle motion is represented by the discrete element approach applying clustered spheres as well as polyhedrons for the particle shape representation. On the CFD-side fluid flow around individual particles is not resolved, but averaged over cells larger than the particles. Various elongated particle shapes are considered including cylinders, plates and cuboids. Comparisons to spherical particles are made. Thereby, the main focuses are mixing which is assessed by the Lacey index, bed height progression and averaged particle orientation. The investigated particle/fluid systems are rich in detail. Large deviations are obtained for the different particle shapes considered. Mixing as well as bed height progression is also strongly influenced by the particle shape. Especially the shape representation accuracy has strong influence on the results as mass and projection area get altered. Significant variations can be obtained for the preferred particle orientations taken up in regions close to the vessel walls in contrast to the interior of a fluidized bed which clearly limits the ability to evaluate processes inside fluidized beds based on visual observations from the exterior only.

Orientation of non-spherical particles in an axisymmetric random flow

AbstractThe dynamics of non-spherical rigid particles immersed in an axisymmetric random flow is studied analytically. The motion of the particles is described by Jeffery’s equation; the random flow is Gaussian and has short correlation time. The stationary probability density function of orientations is calculated exactly. Four regimes are identified depending on the statistical anisotropy of the flow and on the geometrical shape of the particle. If $\boldsymbol{\lambda} $ is the axis of symmetry of the flow, the four regimes are: rotation about $\boldsymbol{\lambda} $, tumbling motion between $\boldsymbol{\lambda} $ and $- \boldsymbol{\lambda} $, combination of rotation and tumbling, and preferential alignment with a direction oblique to $\boldsymbol{\lambda} $.

Particle patterning using fluidics and electric fields

Electric-field manipulation of micro-particles in suspension can create patterns via a number of particle forces and fluid flows. These effects are assessed for their suitability for down-scaling to form nano-patterns such as may be incorporated into structured nano-composites. Consideration is given not only to the assembly of field-aligned chains or wires, but also to methods that can give cross-field assembly and even 2-D patterns or crystals. Dielectrophoresis is often the dominant driving force behind particle assembly, but other dipole-dipole interactions and also electrically-driven fluid flows are increasingly recognized as significant or dominant. Orientation of non-spherical particles in frequency-selectable directions is also possible. Estimates for the threshold field strengths required for using these effects to handle nano-particles are considered. Finally the use of media with modified permittivity to increase the field-induced forces or to optimize the selectivity of particle incorporation is discussed.

Numerical simulations of polarized scattering from random clusters of spatially-orented, non-spherical scatters

Employing multiple scattering formulation of T-matrix method, numerical simulations are developed and applied to polarized scattering from random clusters of spatially-oriented, non-spherical particles. Polarized scattering is numerically presented for the functional dependence on particle shape, size, spatial distribution and orientation, and other physical parameters. Numerical calculations of backscattering from randomly clustered particles are well compared with that from independent particles and clusters. It can be seen that spatial distribution and orientation of non-spherical particles can have significant effect on scattering.

Frequency dependence of electric-field-induced orientation of myelin tubes

Orientation induced by an alternating electric field was studied for myelin tubes of egg phosphatidylcholine (egg-PC) in water and in KCl electrolyte solution. The orientation was also studied for myelin tubes of egg-PC/cholesterol mixtures in water. The orientation effect was measured by the bending curvature of myelin tubes with hairpin-like deformation at frequencies between 10 kHz and 20 MHz. The bending deformation of egg-PC myelin tubes in water decreased abruptly with a decreasing frequency within the low-frequency range below 100 kHz, and shrinkage of myelin tubes was often observed. The bending deformation decreased as the frequency was increased in a higher frequency range. The profile of the frequency dependence for egg-PC in KCl solution was similar to that in water but shifted towards a higher frequency. At low KCl concentrations below 3 mM, the relaxation frequency increased proportionally with increasing an KCl concentration, which was due to a proportional increase in the conductivity of the surrounding medium. Similar profiles of the frequency dependence were observed for egg-PC/cholesterol mixtures but with no shift in the relaxation frequency. These data in the high-frequency range fitted well with calculations based on theoretical equations for the electric-field-induced orientation of nonspherical particles. The conductivity of myelin tubes was estimated to be in the order of 10 −4 S/m in water and of 10 −3 S/m at the low KCl concentrations. The bending modulus of a bilayer membrane was estimated to be (1.0 ± 0.5) · 10 −19 J for egg-PC in water. No change in the bending modulus was observed for egg-PC in KCl solution. However, for egg-PC/cholesterol mixtures in water, the bending modulus abruptly increased to (1.8 ± 0.5) · 10 −19 J at a cholesterol concentration of 40 mol%.

Radiation-induced orientation of atmospheric aerosols

A theoretical model is presented for computing the radiation-induced orientation of nonspherical particles in the atmosphere. This process is examined as a possible remote-sensing technique for determining size and shape characteristics of atmospheric aerosols. The theoretical model is applied to cirrus particles modeled as prolate dielectric spheroids. The radiation-induced perturbations in the average tip angle of the spheroids and in the backscattered depolarization ratio are computed for an assumed radiation flux of 5 mJ/cm2 for three different wavelengths. The computed perturbations are found to be approximately 30–40 dB down from the corresponding unperturbed values and appear marginally detectable by ground-based lidars.

On the orientation of nonspherical particles at solid surfaces. A method of analysis

Abstract The relation between the projected and true linear measures of nonspherical particles at solid surfaces is discussed in terms of an orientation distribution function. It is shown that this function can be determined by a geometric method, which is tested on spheroidal bacterial spores.

Electrical Sizing of Particles in Suspensions: I. Theory

The processes involved during the passage of a suspended particle through a small cylindrical orifice across which exists an electric field are considered in detail. Expressions are derived for the resulting change in current in terms of the ratios of particle to orifice volume and particle to suspending fluid resistivity, and particle shape. Graphs are presented of the electric field and of the fluid velocity as functions of position within the orifice, and of the shape factor of spheroids as a function of their axial ratio and orientation in the electric field. The effects of the electric and hydrodynamic fields on the orientation of nonspherical particles and on the deformation of nonrigid spheres is treated, and the migration of particles towards the orifice axis is discussed. Oscillograms of current pulses produced by rigid, nonconducting spheres in various orifices are shown and compared with the theoretical predictions.

Alternative‐Current Field‐Induced Forces and Their Biological Implications

Steady‐state, field‐induced forces on particles of microscopic size become significant at field strength values of the order of 100 v/cm. They include “pearl‐chain formation,” i.e. the alignment of particles in the direction of the imposed field, and the orientation of nonspherical particles. The time constant, which describes the speed of these phenomena, depends on field strength, and particle and other parameters. For pulsed fields, a lower level of applied average power can suffice to evoke the phenomena mentioned. Biological implications include the possibility of nonthermal effects of biological significance.

Microwave Scattering by Nonspherical Particles

A method for obtaining detailed dependence of extinction cross sections on the orientation of nonspherical particles is described. The results of experimental scattering studies of several different particles are presented.

On the Orientation of Nonspherical Particles in an Alternating Electrical Field

It is shown in general that any nonspherical particle imbedded in a medium with a different complex dielectric constant will experience orienting forces from an impressed alternating electrical field. The direction of stable orientation is determined by the geometry of the particle, by the dielectric properties of the material involved, and also by the frequency of the field. A continuous change of frequency may result in a continuous rotation of the particle as well as in a sudden ``turnover'' covering an angle of 90 deg. The case of an ellipsoid suspended in an isotropic medium is discussed in more detail. If the complex dielectric constant of the ellipsoid can be represented by a tensor with principal axes coinciding with the geometrical axes, the direction of stable orientation always is given by one of these axes. However, the choice of ``stable axis'' may be frequency dependent, so that turnover effects may occur as the frequency is changed. Such behavior is possible even if the dielectric properties of the ellipsoid are isotropic. Similar effects are displayed by a system approximating the passive electrical properties of biological cells in an electrolyte solution, thus accounting for some unusual experimental observations of this kind.

The flow birefringence of solutions of polystyrene in bromoform

THE MOST important source of information on the shape of macromolecules is the s tudy of the birefringence and orientation angles in flowing streams of polymer solutions. The theory that regards the action of flow at very low rate gradients, 9, as the orientation of non-spherical particles leads to the following relationship between the intrinsic value of the orientation angle, [q/g], the molecular weight of the polymer, M, its intrinsic viscosity, [t/J0, and the viscosity of the solvent, t/o f ~ ] =KMtl°[rl]°RT (1)

The Effect of Orientation of Non-Spherical Particles on Interstellar Extinction.

The Effect of Orientation of Non-Spherical Particles on Interstellar Extinction.