Effects of Particle Shapes on Unipolar Diffusion Charging of Non-Spherical Particles

2004 ◽  
Vol 28 (5) ◽  
pp. 501-509
Keyword(s):  
Spherical Particles ◽  
Diffusion Charging ◽  
Particle Shapes

Direct Numerical Simulation of Flow Past a Solid Particle: Influence of Streamline Curvature and Particle Non-Sphericity

2011 ◽  
Author(s):  
Toshiaki Fukada ◽  
Takeshi Omori ◽  
Shintaro Takeuchi ◽  
Takeo Kajishima
Keyword(s):  
Spherical Particle ◽  
Solid Particle ◽  
Point Particle ◽  
Spherical Particles ◽  
Immersed Boundary ◽  
Spheroidal Particle ◽  
Two Phase ◽  
Fluid Force ◽  
Streamline Curvature ◽  
Particle Shapes

Conventional point-particle models for fluid-solid two-phase flows are mainly based on the analysis of the fluid force on a sphere in a uniform stream or a homogeneous shear flow. Their applicability to the flows with (non-zero) streamline curvature and non-spherical particles is yet to be established. In particle segregation in curved flows, the effects of streamline curvature and particle shapes may become significant. In the present study, the hydrodynamic force on a single spherical/spheroidal particle in uniform and curved flow is investigated. The flow around a solid particle is simulated by an immersed-boundary method of a body force type, which has been developed by the authors. The results demonstrate that the spheroidal particle receives higher drag force than the spherical particle. On the other hand, though the effect of the streamline curvature on the fluid force is not clearly observed, the spherical particle rotates only in curved flow.

scholarly journals Mechanical Performances of Typical Robot Feet Intruding into Sands

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1867
Author(s):  
Dianlei Han ◽  
Rui Zhang ◽  
Hua Zhang ◽  
Zhenyu Hu ◽  
Jianqiao Li
Keyword(s):  
Quartz Sand ◽  
The Other ◽  
Legged Robots ◽  
Spherical Particles ◽  
Particle Sizes ◽  
Resistive Force ◽  
The Media ◽  
Resistive Forces ◽  
Mechanical Performances ◽  
Particle Shapes

Four kinds of feet with typical structures, referred to as the hemispherical foot, the semicylindrical foot, the rectangular foot and the circular foot, respectively, were designed and manufactured to study the foot–terrain interaction mechanics for legged robots. Three kinds of quartz sand were selected to study how particle size, shape and compactness affected the physical properties of the substrate and the intrusion performance of mechanical feet. The media with smaller particle sizes had higher bulk densities and lower angles of stability, but no obvious rule was found for particle shapes of quartz sand with different sizes. The intrusion resistive forces and pressures of the hemispherical foot on these three kinds of quartz sand were all less compared with the other three mechanical feet. The particle disturbance areas and motion trends were compared under these four kinds of mechanical feet using discrete element method simulations. The intrusion resistive forces of these mechanical feet first increased and then decreased with the increasing particle sizes of the quartz sand. Moreover, the intrusion resistive forces of these mechanical feet on spherical particles were smaller compared with irregular particles. The corresponding resistive forces of the mechanical feet were characterized based on the compactness of the quartz sand. According to the intrusion test data, the classic pressure–sinkage model was modified, and the relationships between intrusion resistive force and mechanical foot depth were obtained.

The Sintered Porous Metal Media Development and Measurement of LHP Systems for Electronic Cooling Device

2008 ◽  
Author(s):  
Byung-ho Sung ◽  
Jeehoon Choi ◽  
Jaehyung Ki ◽  
Junghyun Yoo ◽  
Minwhan Seo ◽  
...  
Keyword(s):  
Porous Metal ◽  
Spherical Particles ◽  
Flow Properties ◽  
Cooling Device ◽  
Continuous Increase ◽  
Electric Device ◽  
Experimental Apparatus ◽  
Wick Structure ◽  
Set Up ◽  
Particle Shapes

Due to the continuous increase of power applied in electric device, the growing demand on cooling systems have led with using various cooling device to conduct the thermal management. As a new cooling device, a Loop Heat Pipe (LHP) system has been taken notice recently. The performance of the LHP systems depends mainly upon the operating performance of the wick structure should possess flow properties such as permeability, maximum capillary pressure and so on. However, expressions on packed metal spherical particles are not related with various particle shapes. In this work, therefore, an experimental apparatus was set up to measure the flow properties of sintered porous metal wicks manufactured with spherical, needled, and corn shape particles. The results of the such experiments gave very accurate and consistent.

Kinetic Simulations for Analysing the Wall Collision Process of Non-Spherical Particles

2002 ◽  
Author(s):  
M. Sommerfeld
Keyword(s):  
Particle Shape ◽  
Fluid Dynamic ◽  
Impact Angle ◽  
Distribution Functions ◽  
Spherical Particles ◽  
Collision Process ◽  
Wall Collision ◽  
Particle Velocities ◽  
The Impact ◽  
Particle Shapes

In wall-bounded gas-solid flows the wall collision process plays an important role and may be strongly affected by wall roughness and particle shape. The modelling of the particle-wall collision mostly relies on the assumption of spherical particles. To extend such models appropriately for non-spherical particles, two-dimensional kinetic simulations were performed for different particle shapes. This implies, that the particle translational and angular motion is calculated by considering the particle shape, however neglecting fluid dynamic effects. The change of the particle velocities during the impact and rebound process was calculated by solving the impulse equations together with Coulombs law of friction. The simulations were performed for a given initial particle velocity by varying impact angle and initial angular velocity. The results for 2000 particle wall collisions allowed us to derive the distribution functions of the impact parameters required to describe the wall collision process for non-spherical particles correctly. Moreover, other wall collision properties, such as rebound angle and velocity ratios could be determined. Finally also a comparison with measurements was possible.

Microscopic analysis of shape-shiftable oligo(ε-caprolactone) - based particles

MRS Advances ◽  
2019 ◽  
Vol 4 (59-60) ◽  
pp. 3199-3206
Author(s):  
Fabian Friess ◽  
Christian Wischke ◽  
Andreas Lendlein
Keyword(s):  
Aspect Ratio ◽  
Microscopic Analysis ◽  
Contour Detection ◽  
The Body ◽  
Water Soluble ◽  
Spherical Particles ◽  
Thermally Induced ◽  
Alternative Techniques ◽  
Particle Shapes ◽  
Prolate Ellipsoidal

ABSTRACTSpherical particles are routinely monitored and described by hydrodynamic diameters determined, e.g., by light scattering techniques. Non-spherical particles such as prolate ellipsoids require alternative techniques to characterize particle size as well as particle shape. In this study, oligo(ε-caprolactone) (oCL) based micronetwork (MN) particles with a shape-shifting function based on their shape-memory capability were programmed from spherical to prolate ellipsoidal shape aided by incorporation and stretching in a water-soluble phantom matrix. By applying light microscopy with automated contour detection and aspect ratio analysis, differences in characteristic aspect ratio distributions of non-crosslinked microparticles (MPs) and crosslinked MNs were detected when the degrees of phantom elongation (30-290%) are increased. The thermally induced shape recovery of programmed MNs starts in the body rather than from the tips of ellipsoids, which may be explained based on local differences in micronetwork deformation. By this approach, fascinating intermediate particle shapes with round bodies and two opposite sharp tips can be obtained, which could be of interest, e.g., in valves or other technical devices, in which the tips allow to temporarily encage the switchable particle in the desired position.

scholarly journals The Effect of Particle Shapes on the Field-Dependent Rheological Properties of Magnetorheological Greases

2019 ◽  
Vol 20 (7) ◽  
pp. 1525 ◽  
Author(s):  
Norzilawati Mohamad ◽  
Ubaidillah ◽  
Saiful Mazlan ◽  
Seung-bok Choi ◽  
Siti Abdul Aziz ◽  
...  
Keyword(s):  
Transient Response ◽  
Electrical Current ◽  
High Energy ◽  
Spherical Particles ◽  
Principal Characteristics ◽  
Weight Percentage ◽  
Storage And Loss Moduli ◽  
Field Dependent ◽  
External Stimuli ◽  
Particle Shapes

The transient response of magnetorheological (MR) materials, in general, is very important for design consideration in MR-based devices. Better response to magnetic fields is beneficial for a better response rate to the electrical current applied in the electromagnetic coil. As a result, MR-based devices would have a high response to external stimuli. In this work, the principal characteristics of magnetorheological greases (MRGs) which have two different particle shapes are experimentally investigated. One type of particle distributed in the grease medium is conventional spherical-shaped carbonyl iron (CI) particles, while the other is plate-like CI particles made using a high-energy rotary ball mill from spherical CI particles. A set of bidisperse MRG samples are firstly prepared by adjusting the weight percentage of the plate-like CI particles and mixing with the spherical CI particles. Subsequently, three important properties of MRGs in terms of their practical application are measured and compared between the two different particle shapes. The field-dependent apparent viscoelastic properties of the prepared MRG samples are measured, followed by the field-dependent storage and loss moduli using an oscillatory shear rheometer. In addition, the transient response time, which indicates the speed in the actuating period of MRGs, is measured by changing the strain amplitude. Then, a comparative assessment on the three properties are undertaken between two different particle shapes by presenting the corresponding results in the same plot. It is shown that the bidisperse MRG with plate-like CI particles exhibits an increase in the initial apparent viscosity as well as stiffness property compared to the MRG with spherical particles only.

scholarly journals Motion of a sphere in the presence of a plane interface. Part 2. An exact solution in bipolar co-ordinates

1980 ◽  
Vol 98 (1) ◽  
pp. 193-224 ◽  
Author(s):  
S. H. Lee ◽  
L. G. Leal
Keyword(s):  
Exact Solution ◽  
General Solution ◽  
Approximate Solutions ◽  
Plane Interface ◽  
Spherical Particles ◽  
Fluid Interface ◽  
Two Fluids ◽  
Freely Suspended ◽  
Velocity Pressure ◽  
Particle Shapes

A general solution for Stokes’ equation in bipolar co-ordinates is derived, and then applied to the arbitrary motion of a sphere in the presence of a plane fluid/fluid interface. The drag force and hydrodynamic torque on the sphere are then calculated for four specific motions of the sphere; namely, translation perpendicular and parallel to the interface and rotation about an axis which is perpendicular and parallel, respectively, to the interface. The most significant result of the present work is the comparison between these numerically exact solutions and the approximate solutions from part 1. The latter can be generalized to a variety of particle shapes, and it is thus important to assess their accuracy for this case of spherical particles where an exact solution can be obtained. In addition to comparisons with the approximate solutions, we also examine the predicted changes in the velocity, pressure and vorticity fields due to the presence of the plane interface. One particularly interesting feature of the solutions is the fact that the direction of rotation of a freely suspended sphere moving parallel to the interface can either be the same as for a sphere rolling along the interface (as might be intuitively expected), or opposite depending upon the location of the sphere centre and the ratio of viscosities for the two fluids.

Numerical Simulation and Modelling of the Forces Acting on Single and Multiple Non-Spherical Particles

2014 ◽  
Author(s):  
Rafik Ouchene ◽  
Amine Chadil ◽  
Pascal Fede ◽  
Mohammed Khalij ◽  
Anne Tanière ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Turbulent Flows ◽  
Large Range ◽  
Direct Numerical Simulations ◽  
Particle Orientation ◽  
Spherical Particles ◽  
Ellipsoidal Particle ◽  
Particle Shapes

The paper deals with gas-solid turbulent flows carrying non-spherical particles. The main objective of the present paper is to compute the hydrodynamics forces on non-spherical particles as a function of the particle orientation, for different particle shapes and a large range of particle Reynolds number. Two Direct Numerical Simulations at the scale of the particle are used, i.e. a body-fitted approach and a viscous penalty approach, in the case of a uniform flow with a single ellipsoidal particle. Results are compared with several correlations from the literature and a new proposal for the drag coefficient is given. The study is then extended to the case of a lattice of non-spherical particles to measure the pressure drop and to connect it with the drag coefficient.

scholarly journals The Bipolar Diffusion Charging of Nanoparticles: A Review and Development of Approaches for Non-Spherical Particles

2015 ◽  
Vol 49 (12) ◽  
pp. 1181-1194 ◽  
Author(s):  
Ranganathan Gopalakrishnan ◽  
Peter H. McMurry ◽  
Christopher J. Hogan,
Keyword(s):  
Spherical Particles ◽  
Diffusion Charging

scholarly journals Technical Note: Optical properties of desert aerosol with non-spherical mineral particles: data incorporated to OPAC

2015 ◽  
Vol 15 (10) ◽  
pp. 5947-5956 ◽  
Author(s):  
P. Koepke ◽  
J. Gasteiger ◽  
M. Hess
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Technical Note ◽  
Spherical Particles ◽  
Refractive Indices ◽  
Size Distributions ◽  
Actual Case ◽  
Size Dependent ◽  
Mineral Particles ◽  
Particle Shapes

Abstract. Mineral particles, in general, are not spheres and so the assumption of spherical particles, instead of more realistic shapes, has significant effects on modeled optical properties and therefore on remote-sensing procedures for desert aerosol and the derived radiative forcing. Thus, in a new version of the database OPAC (Optical Properties of Aerosols and Clouds; Hess et al., 1998), the optical properties of the mineral particles are modeled describing the particles as spheroids with size dependent aspect ratio distributions, but with the size distributions and the spectral refractive indices not changed against the previous version of OPAC. The spheroid assumption is known to substantially improve the scattering functions but pays regard to the limited knowledge on particle shapes in an actual case. The relative deviations of the optical properties of non-spherical mineral particles from those of spherical particles are for the phase function in the solar spectral range up to +60% at scattering angles of about 130° and up to −60% in the backscatter region, but less than 2% for the asymmetry parameter. The deviations are generally small in the thermal infrared and for optical properties that are independent of the scattering angle. The improved version of OPAC (4.0) is freely available at www.rascin.net.

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