Effect of Ellipsoidal Particle Shape on Tribological Properties of Lubricants Containing Nanoparticles

Adding nanoparticles can significantly improve the tribological properties of lubricants.However,there is a lack of understanding regarding the influence of nanoparticle shape on lubrication performance.In this work,the influence of diamond nanoparticles(DNPs)on the tribological properties of lubricants is investigated through friction experiments.Additionally,the friction characteristics of lubricants regarding ellipsoidal particle shape are investigated using molecular dynamics(MD)simulations.The results show that DNPs can drastically lower the lubricant's friction coefficientμfrom 0.21 to 0.117.The shearing process reveals that as the aspect ratio(α)of the nanoparticles approaches 1.0,the friction performance improves,and wear on the wall diminishes.At the same time,the shape of the nanoparticles tends to be spherical.When 0.85≤α≤1.0,rolling is ellipsoidal particles'main form of motion,and the friction force changes according to a periodic sinusoidal law.In the range of 0.80≤α<0.85,ellipsoidal particles primarily exhibit sliding as the dominant movement mode.Asαdecreases within this range,the friction force progressively increases.The friction coefficientμcalculated through MD simulation is 0.128,which is consistent with the experimental data.

Comparison of Construction Method for DEM Simulation of Ellipsoidal Particles

Discrete element model was developed to simulate the ellipsoidal particles moving in the moving bed. Multi-element model was used to describe a ellipsoidal particle, the contact detection algorithm of ellipsoidal particle was developed, and both contact force and gravity force were considered in the models. The simulation results were validated by our experiment. Three algorithms for representing an ellipsoidal particle were compared in macro and micro aspects. The results show that there exists big difference in the microscopic parameters such as kinetic energy, rotational kinetic energy, deformation, contact force and collision number which leads to the difference of macroscopic parameters. The relative error in the discharge rate and tracer particle position is the largest between 3-tangent-element representation and experimental results. The flow pattern is similar for the 5-element and 3-intersection representations. The only difference is the discharge rate of 5-element representation is larger than the experimental value and that of the 3-intersection representation has the contrary result. Finally the 3-intersection- element reoresentation is chosen in the simulation due to less comouting time than that of the 5-element renresentation.

Numerical investigation on motion of an ellipsoidal particle inside confined microcavity flow

The behaviors of a neutrally buoyant ellipsoidal particle in vortical flow confined by a microcavity are numerically studied using the Lattice-Boltzmann method.For specific initial position,an isolated ellipsoid may develop a stable limit cycle orbit inside microcavity due to the interaction between particle and the carrier flow.It is observed that ellipsoidal particles of different shapes exhibit two different stable rotational modes depending on the initial orientation and lateral position.A prolate spheroid tends to enter a tumbling mode whereas an oblate spheroid is apt to achieve a rolling mode.The evolution of rotational velocities along the stable orbit is also analyzed for particles of different shapes.

Numerical evaluation of overestimation of the interface thickness around ellipsoidal particle

Abstract When interfacial layers are viewed as a separate phase, the interface thickness plays an essential role in assessing physico-mechanical properties of particulate materials. However, the interface thickness from sectional analysis is often overestimated, due to the irregularity of surface textures of grains in opaque materials that gives rise to the normal of a cross-sectional plane non-perpendicular to the surface of grains. Hence, the determination of the overestimation degree is very critical to precisely obtain the interface thickness. This article develops a numerical model for the overestimation degree of the interface thickness around an ellipsoidal grain with an arbitrary aspect ratio, by applying an accurate sectional analysis algorithm, and quantitative stereology and geometrical probability theories. Furthermore, on the basis of the developed numerical model, the influence of ellipsoidal particle shape on the overestimation degree is quantitatively charac-terized.

Morphology of impact fragmentation distribution of single spherical and ellipsoidal particles in drop weight experiments

Particle shape is an important factor affecting the fragmentation distribution of the ore particles.To investigate the influence of particle shape on the morphological fragmentation distribution characteristics,the crushable ore particles are defined as prolate,oblate ellipsoid and spherical particles,which have different aspect ratios(AR)and sphericity(S).Based on the drop weight experiment,the influence of the net drop height on the macroscopic mechanical behavior and crushing distribution characteristics of the single spherical and ellipsoidal particles is studied.The results show that different peak-shifting characteristics exist during particle fragmentation.The fragmentation distribution peak shifts left when the increased impact energy is eventually only enough to break medium-sized sub-particles.Conversely,it shifts right when impact energy is increased enough to break largest-sized sub-particles.Besides,regardless of whether the net drop height changes,the maximum continuous fragmentation degree presents"M"-shaped characteristic with the increased AR.Compared with the ellipsoid particles,the single spherical particle is more difficult to be broken by impact,with wider equivalent particle fragmentation distribution.With the increase of particle sphericity,the maximum continuous fragmentation degree of a single ellipsoid particle has an overall trend of initial increase and subsequent decrease.Especially when particle sphericity is 0.9<S<0.95,the maximum continuous fragmentation degree of both prolate and oblate ellipsoid particles is much higher.

Experimental study of an ellipsoidal particle in tube Poiseuille flow

Behaviors of a prolate ellipsoid inside circular tube Poiseuille flow are studied experimentally. In the study, Reynolds number Re ∈ (100,700) and the confinement ratio D/A ∈ (1.2,2.8) are considered, where D is the diameter of the tube and A is the length of the major axis of the ellipsoid. Two typical stable motion modes are identified, namely, the horizontal, and inclined modes. Then another inclined mode (inclined mode II) is found at high Reynolds number (Re ∈ (1000,3200)) and small D/A, and the inclined angle of ellipsoid increases with the increase of Re. The possible mechanism is explained. Our experiment shows that the lagging velocity U increases as Re increases. Further numerical analysis using FLUENT shows that due to the increase of U, the moment acting on the particle would make the inclined angle of the particle increase.

An experiment for obtaining DOP ellipsoid using particle swarm optimization algorithm

The degree of polarization (DOP) ellipsoid can be used as either feedback or feedforward signal for automatic polarization mode dispersion compensation. We have realized the experiment for obtaining DOP ellipsoid from 100 sampling data of output states of polarization using particle swarm optimization (PSO) as ellipsoid data fitting algorithm. It was shown that the PSO algorithm was powerful for ellipsoid data fitting with high precision within 250 ms.

Flow behavior of non-spherical particle flowing in hopper

Ellipsoidal particles flowing in the hopper were simulated by using the discrete element method （DEM）, and described by the multi-element method. The contact detection algorithm and equations for ellipsoidal particle motion in hopper were developed. And the simulation results were confirmed by experiment. Additionally, the mass flow rate, pressure distribution and velocity distribu- tion of two kinds of particles were examined. The results show that the mass flow rate of ellipsoidal particles is smaller than that of spherical particles. There is a maximum value of pressure drop at the top of the junction. Besides, the pressure drop decreases with the discharging time increasing. The velocity of spherical particle is larger than that of ellipsoidal.

Numerical reconstruction of microstructure of graphite anode of lithium-ion battery

Due to the presence of graphite flake cascades, the real graphite anode of Li-ion battery shows non-iso- tropic characteristic. The present work developed an ellipsoid-based simulated annealing method and numeri- cally reconstructed the three-dimensional microstructure of a graphite anode. The reconstructed anode is a composite of three clearly distinguished phases： pore （or electrolyte）, graphite, and solid additives, well representing the non- isotropic heterogeneous characteristic of real graphite anode. Characterization analysis of the reconstructed electrode gives information such as the connectivity of individual phase, the specific interracial area between solid and pore phase, and the pore size distribution. The effects of the ellipsoid size on the structural characteristics of graphite anode were particularly studied. As the size of the ellipsoidal particle slightly increases, the average pore diameter increases and as a result the specific interfacial area between the solid and pore phase in the reconstructed area decreases; compared with the equatorial radius, the polar radius of ellipsoidal graphite particles has more sig- nificant influence on the characteristics of electrode microstructure.