Prolate Ellipsoidal Particles Research Articles

Computational study on interaction between rotating non-spherical particles and shear-thinning fluids

In this paper, the drag coefficient (Cd), lift coefficient (Cl), and torque coefficient (Ct) of rotating non-spherical particles in shear-thinning non-Newtonian fluids are investigated based on particle-resolved direct numerical simulation. The Carreau model is used to describe the rheological behavior of non-Newtonian fluids, and the numerical model is validated against previously published data. Then, the effects of aspect ratio (Ar), spin number (Spa), flow index (n), and Carreau number (Cu) on Cd, Cl, and Ct of rotating non-spherical particles are investigated at different Reynolds numbers (Re). The numerical results show that the closer the particles are to the spherical shape, the smaller the fluctuations of Cd, Cl, and Ct curves. The peaks and valleys of Cd, Cl, and Ct of oblate and prolate ellipsoidal particles are reversely distributed. The fluctuations of Cd and Cl curves increase with increasing Spa. Cd decreases with increasing Spa at low Re, contrary to Newtonian fluids' results. Cd and Ct decrease with increasing shear-thinning properties, Cl increases with increasing shear-thinning properties, and the effect of shear-thinning properties decreases with increasing Re. The variation of viscosity and pressure is the main reason for the variation of Cd, Cl, and Ct under different variables. Predictive correlations of Cd and Ct are established based on Re, Spa, n, Cu, and α. The findings indicate that particle rotation and shear-thinning properties must be considered when evaluating particle-fluid interactions, which provide important guidance for predicting and controlling the orientation and distribution of non-spherical particles in non-Newtonian fluids.

Self Assembly of Patchy Anisotropic Particle Forming Free Standing Monolayer Film (Adv. Theory Simul. 3/2023)

The phase diagram of prolate ellipsoidal particles shows the co-existence of two types of HCP crystals with the gas particles. Through thermodynamic calculation it is established that a free-standing monolayer having an HCP arrangement co-exist with the gas particles in a small region of the phase diagram. This is reported by Sujin B. Babu and co-workers in article number 2200666.

Dynamics of prolate spheroids in the vicinity of an air-water interface.

In this article, we present the mobilities of prolate ellipsoidal micrometric particles close to an air-water interface measured by dual wave reflection interference microscopy. Particle's position and orientation with respect to the interface are simultaneously measured as a function of time. From the measured mean square displacement, five particle mobilities (3 translational and 2 rotational) and two translational-rotational cross-correlations are extracted. The fluid dynamics governing equations are solved by the finite element method to numerically evaluate the same mobilities, imposing either slip and no-slip boundary conditions to the flow at the air-water interface. The comparison between experiments and simulations reveals an agreement with no-slip boundary conditions prediction for the translation normal to the interface and the out-of-plane rotation, and with slip ones for parallel translations and in-plane rotation. We rationalize these evidences in the framework of surface incompressibility at the interface.

Lipid nanoparticles with erythrocyte cell-membrane proteins

When the separated erythrocyte membranes (known as ghosts) are ultrasonicated, a significant part of the membrane proteins are released in the aqueous solvent, instead of being incorporated into the membranes of the formed nanoerythrosomes. In contrast to their membrane-bound counterparts, where helices and β-strands dominate, the released proteins show perturbed secondary structures with an increased ratio of helices, presumably participating in molten globules, as it has been revealed by circular dichroism (CD) and infra-red spectroscopy (IR). The shape and size of these proteins is diverse, and even their aggregates appear. When excess lipid (palmitoyl-lysophosphatidylcholine, LPC) is added to different ghost-derivatives (the full nanoerythrosome system, and its ultracentrifugation pellet and supernatant) in 2 × and 5 × lipid-to-protein mass ratio, various lipid nanoparticles are produced. The core–shell and nanodisc structural models obtained by small-angle X-ray scattering (SAXS) indicate that the choice of the precursor system has a more prominent effect on the resulting shape than the amount of lipid added: when starting from the protein-rich supernatant fraction, small (approx. 5 nm high and 7 nm wide) nanodisks are created. When lipid membranes are already present (in the pellet and the full nanoerythrosome fraction), similar LPC addition results in prolate ellipsoidal particles, with an aspect ratio between 3 and 5, and decreasing overall size when the amount of added lipid is increased. The ellipsoids formed from the total nanoerythrosome fraction are smaller than those from the ultracentrifugation pellet (longest axis around 15 vs 26 nm), whereas for higher LPC-to-protein ratio, the size in both cases reduce to nearly the same (13–14 nm) in both cases.

Predictive Shapes of Ellipsoid PPDL-PTHF Copolymer Particles Prepared by the Phantom Stretching Technique.

Ellipsoidal polymer particles can be prepared from spheres by unidirectional stretching at elevated temperatures, while the particles’ aspect ratios (AR) that result from this phantom stretching methodology are often not precisely predictable. Here, an elastic deformation model was exemplarily evaluated for ~50 µm spherical microparticles from PPDL-PTHF block copolymers. The prolate ellipsoidal particles, obtained by stretching in polyvinyl alcohol phantoms, differed in dimensions at identical relative phantoms elongations up to 150%, depending on the relative polymer composition and their systematically altered mechanical properties. Importantly, the resulting particle shapes within the studied range of AR up to ~4 matched the predictions of the elastic deformation model, which includes information of the elastic moduli of phantom and particle materials. These data suggest that the model may be applicable to predict the conditions needed to precisely prepare ellipsoids of desired AR and may be applicable to various deformable particle materials.

Drag and lift coefficients of ellipsoidal particles under rarefied flow conditions.

The capability to simulate a two-way coupled interaction between a rarefied gas and an arbitrary-shaped colloidal particle is important for many practical applications, such as aerospace engineering, lung drug delivery, and semiconductor manufacturing. By means of numerical simulations based on the direct-simulation Monte Carlo (DSMC) method, we investigate the influence of the orientation of the particle and rarefaction on the drag and lift coefficients, in the case of prolate and oblate ellipsoidal particles immersed in a uniform ambient flow. This is done by modeling the solid particles using a cut-cell algorithm embedded within our DSMC solver. In this approach, the surface of the particle is described by its analytical expression and the microscopic gas-solid interactions are computed exactly using a ray-tracing technique. The measured drag and lift coefficients are used to extend the correlations, based on the sine-squared drag law, available in the continuum regime to the rarefied regime, focusing on the transitional and free-molecular regimes. The functional forms of the correlations for the ellipsoidal particles are chosen as a generalization from the spherical case. We show that the fits over the data from numerical simulations can be extended to regimes outside the simulated range of Kn. Our approach allows to achieve a higher precision when compared with existing predictive models from the literature. Finally, we underline the importance of this work in providing correlations for nonspherical particles that can be used for point-particle Euler-Lagrangian simulations to address the problem of contamination from finite-size particles in high-tech mechanical systems.

Analysis of particle shape effect on the discharging of non-spherical particles in HTR-10 reactor core

The discharge flow characteristics of particles are crucial in many industrial applications, and the shape of particle is an important influencing factor to the particle flow behavior. In this study, the discrete element method (DEM) was adopted to analyze the discharge flow of non-spherical particles in HTR-10 reactor core. After model validation, the shape effect on particle flow in hopper was analyzed. The super-ellipsoid model was used to the comparative study of particles with 5 different shapes which can represent a large number of shapes, including oblate ellipsoidal particles, prolate ellipsoidal particles, circular cylindrical particles, elliptical cylindrical particles, and cubical particles, respectively. The results showed that the more stable the packing structure, the higher the efficiency of the stacked volume. But the mobility of these particles was worse than particles with good flow properties. The increase in the blockness (n1 and n2) will make the fluidity of the particles worse, and the particles with aspect ratio (Ra) between 1.5–2 show better discharge behavior. Both the axial and radial velocity can be influenced by particle shape significantly, which will result in different discharge behavior. Rotation angle and direction angle distribution are introduced to analyze the rotation motion. Cylindrical particles showed the most obvious rotation, while the ellipsoidal particles rotated in a relatively small range.

Numerical investigation on the mutual interaction between heat transfer and non-spherical particle dynamics in the blast furnace raceway

In this paper, the coupled computational fluid dynamics (CFD) and discrete element method (DEM) scheme is used to investigate the microstructure and heat transfer characteristics in a blast furnace (BF) raceway. The impact of gas velocity and particle shape on raceway evolution, microstructure characteristics, and particle temperature and voidage distributions is comprehensively explored based on the voidage change caused by the consumption of coke particles. Numerical results show that the oblate ellipsoidal particle system possesses higher average voidage in the original packing state and implements the faster burden descending rate than the prolate one under the same inlet velocity. For the non-spherical particle systems, larger contact forces exist in the oblate ellipsoidal particle system while the contact forces in the prolate ellipsoidal particle system are smaller. More uniform temperature distribution and higher average voidage can be caused by higher inlet gas velocities. Meanwhile, more prolate ellipsoidal particles are consumed than oblate ones under the same inlet velocity. These findings could be beneficial for understanding the kinetic and thermodynamic behaviors of particulate system within a BF raceway.

Effect of particle orientation on the drag force in random arrays of prolate ellipsoids in low‐Reynolds‐number flows

AbstractDirect numerical simulations are performed to study the effect of particle orientation on flows through fixed random arrays of prolate ellipsoids at low Reynolds numbers. The Hermans orientation factor and Beta distribution are introduced to quantify the mean orientation and orientation deviation of the particles. The simulation results show that the effect of particle orientation is profound especially when the solid volume fraction and the aspect ratio are large. With the increase of Hermans orientation factors, the drag force decreases when the flow follows a reference direction defined by the average direction of all particles' semi‐major axes, while increases when the flow is perpendicular to the reference direction. Comparisons show that the traditional drag force correlations for ellipsoidal particles significantly under‐predict the drag force. Based on current simulation results, new drag relations are proposed for prolate ellipsoidal particles at arbitrary aspect ratios, Hermans orientation factors and solid volume fractions.

CFD-DEM study on heat transfer characteristics and microstructure of the blast furnace raceway with ellipsoidal particles

Coupled computational fluid dynamics and discrete element method (CFD-DEM) simulations are carried out to investigate the heat transfer characteristics and microstructure of the blast furnace (BF) raceway with different particle shapes. Three kinds of particles are considered including prolate and oblate ellipsoidal particles and spheres. The coupled CFD-DEM model is first validated based on experimental data and the capability of the combined sphere method (CSM) to investigate the heat transfer is also demonstrated. Then, the validated model is used to systematically explore formation and evolution of the BF raceway, particle behavior, force structure, heat transfer and temperature distribution with the effect of particle shapes on these issues discussed. Numerical results show that the raceway size formed by prolate ellipsoidal particles is the smallest among the three cases whereas the coordination number of which is the highest. Uniform contact force networks and typical orientation inclined angles of ellipsoidal particles influence the stable packing structure and homogeneous void distribution therein. The large surface area and homogeneous void structure of ellipsoidal particles can enhance the convective heat transfer. All the aforementioned factors collectively promote ellipsoidal particles to possess higher heat transfer efficiency than spheres. These findings could be helpful for the design and optimization of the BF.

Influence of anisotropic nanoparticles on the deposition pattern of an evaporating droplet

The suppression or enhancement of the "coffee ring" effect depends on whether nanoparticles easily adhere to the gas-liquid interface and particle shape. To obtain deposition patterns of suspensions of nanoparticles strongly deviating from spheres, which is less studied in the literature, prolate ellipsoidal and cylindrical rod-shaped particles with a minimum aspect ratio of 4 are selected. Dynamic viscosity, which is a function of particle shape and volume fraction, is introduced into the evolution equations for film thickness and particle concentration. The nanoparticle deposition features and the contact line dynamics are examined numerically, and the effect of particle shape on the drying process is analysed. The results show that the contact line is in the depinning state during the droplet shrinkage, while the concentration and effective layer thickness of nanoparticles in the ring-formation region decrease with time, and the deposition band widens. The deposition ring height increases, and the recession of the contact line slows down with increasing aspect ratio. This means that for nanoparticles deviating strongly from spheres and not easily adhering to the gas-liquid interface, the "coffee ring" effect is enhanced when the suspension dries. A larger aspect ratio leads to a more obvious "coffee ring" feature.

Clustering of microswimmers: interplay of shape and hydrodynamics.

The spatiotemporal dynamics in systems of active self-propelled particles is controlled by the propulsion mechanism in combination with various direct interactions, such as steric repulsion and hydrodynamics. These direct interactions are typically anisotropic, and come in different "flavors", such as spherical and elongated particle shapes, pusher and puller flow fields, etc. The combination of the various aspects is expected to lead to new emergent behavior. However, it is a priori not evident whether shape and hydrodynamics act synergistically or antagonistically to generate motility-induced clustering (MIC) and phase separation (MIPS). We employ a model of prolate spheroidal microswimmers-called squirmers-in quasi-two-dimensional confinement to address this issue by mesoscale hydrodynamic simulations. For comparison, non-hydrodynamic active Brownian particles (ABPs) are considered to elucidate the contribution of hydrodynamic interactions. For spherical particles, the comparison between ABPs and hydrodynamic-squirmer ensembles reveals a suppression of MIPS due to hydrodynamic interactions. Yet, our analysis shows that dynamic clusters exist, with a broad size distribution. The fundamental difference between ABPs and squirmers is attributed to an increased reorientation of squirmers by hydrodynamic torques during their collisions. In contrast, for elongated squirmers, hydrodynamics interactions enhance MIPS. The transition to a phase-separated state strongly depends on the nature of the swimmer's flow field-with an increased tendency toward MIPS for pullers, and a reduced tendency for pushers. Thus, hydrodynamic interactions show opposing effects on MIPS for spherical and elongated microswimmers, and details of the propulsion mechanism of biological microswimmers may be very important to determine their collective behavior.

Application limits of Jeffery’s theory for elongated particle torques in turbulence: a DNS assessment

Non-spherical particles suspended in fluid flows are subject to hydrodynamic torques generated by fluid velocity gradients. For small axisymmetric particles, the most popular formulation of hydrodynamic torques is that given by Jeffery (Proc R Soc Lond A 102:161–179, 1922), which is valid for uniform shear flow in the viscous Stokes regime. In the lack of simple alternative formulations outside the Stokes regime, the Jeffery formulation has been widely applied to inertial particles in turbulent flows, where it is bound to produce inaccurate results. In this paper we quantify the statistical error incurred when the Jeffery formulation is used to study the motion of elongated axisymmetric particles under nonlinear shear flow conditions. Considering the archetypical case of prolate ellipsoidal particles in turbulent channel flow, we show that error for ellipsoids of the same length, l, as the Kolmogorov scale of the flow, $$\eta _K$$ , is indeed small (order $$1\%$$ ) but increases exponentially up to $$l \simeq 10 \eta _K$$ before becoming almost independent of elongation.

Behaviors of ellipsoidal micro-particles within a two-beam optical levitator

The two-beam levitator (TBL) is a standard optical setup made of a couple of counter-propagating beams. Note worthily, TBLs allow the manipulation and trapping of particles at long working distances. While much experience has been accumulated in the trapping of single spherical particles in TBLs, the behaviors of asymmetrical particles turn out to be more complex, and even surprising. Here, we report observations with prolate ellipsoidal polystyrene particles, with varying aspect ratio and ratio of the two beam powers. Generalizing the earlier work by Mihiretie et al. in single beam geometries [JQSRT 126, 61 (2013)], we observe that particles may be either static, or permanently oscillating, and that the two-beam geometry produces new particle responses: some of them are static, but non-symmetrical, while others correspond to new types of oscillations. A two-dimensional model based on ray-optics qualitatively accounts for these configurations and for the “primary” oscillations of the particles. Furthermore, levitation powers measured in the experiments are in fair agreement with those computed from GLMT (Generalized Lorentz Mie Theory), MLFMA (Multilevel Fast Multipole Algorithm) and approximate ray-optics methods.

A new set of correlations of drag, lift and torque coefficients for non-spherical particles and large Reynolds numbers

In this paper, we derive and validate new correlations for the drag, lift and pitching torque coefficients for non-spherical particles and a large range of Reynolds numbers Rep and aspect ratios w∈[1−32]. The functional forms of these correlations, depending on Rep, w and incidence angle, α are determined by fitting the results extracted from DNS computations of the flow around prolate ellipsoidal particles. This work follows that of Ouchene et al. [1] in which the numerical method was implemented and validated. A complete set of correlations for prolate ellipsoidal particles outside Stokes regime is provided.

Contact Angles of Microellipsoids at Fluid Interfaces

The wetting of anisotropic colloidal particles is of great importance in several applications, including Pickering emulsions, filled foams, and membrane transduction by particles. However, the combined effect of shape and surface chemistry on the three-phase contact angle of anisotropic micrometer and submicrometer colloids has been poorly investigated to date, due to the lack of a suitable experimental technique to resolve individual particles. In the present work, we investigate the variation of the contact angle of prolate ellipsoidal colloids at a liquid-liquid interface as a function of surface chemistry and aspect ratio using freeze-fracture shadow-casting cryo-SEM. The method, initially demonstrated for spherical colloids, is extended here to the more general case of ellipsoids. The prolate ellipsoidal particles are prepared from polystyrene and poly(methyl methacrylate) spheres using a film stretching technique, in which cleaning steps are needed to remove all film material from the particle surface. The effects of the preparation protocol are reported, and wrinkling of the three-phase contact line is observed when the particle surface is insufficiently cleaned. For identically prepared ellipsoids, the cosine of the measured contact angle is, in a first approximation, a linearly decreasing function of the contact line length and thus a decreasing function of the aspect ratio. Such a trend violates Young-Laplace's equation and can be rationalized by adding a correction term to the ideal Young-Laplace contact angle that expresses the relative importance of line effects relative to surface effects. From this term the contribution of an effective line tension can be extracted. This contribution includes the effects that both surface chemical and topographical heterogeneities have on the contact line and which become increasingly more important for ellipsoids with higher aspect ratios, where the contact line length to contact area ratio increases.

Rotational and translational diffusion of anisotropic gold nanoparticles in liquid crystals controlled by varying surface anchoring

We study translational and rotational diffusion of anisotropic gold nanoparticles (NPs) dispersed in the bulk of a nematic liquid crystal fluid host. Experimental data reveal strong anisotropy of translational diffusion with respect to the uniform far-field director, which is dependent on shape and surface functionalization of colloids as well as on their ground-state alignment. For example, elongated NPs aligned parallel to the far-field director translationally diffuse more rapidly along the director whereas diffusion of NPs oriented normal to the director is faster in the direction perpendicular to it while they are also undergoing elasticity-constrained rotational diffusion. To understand physical origins of these rich diffusion properties of anisotropic nanocolloids in uniaxially anisotropic nematic fluid media, we compare them to diffusion of prolate and oblate ellipsoidal particles in isotropic fluids as well as to diffusion of shape-isotropic particles in nematic fluids. We also show that surface functionalization of NPs with photosensitive azobenzene groups allows for in situ control of their diffusivity through trans-cis isomerization that changes surface anchoring.

On semiautomatic estimation of surface area

In this paper, we propose a semiautomatic procedure for estimation of particle surface area. It uses automatic segmentation of the boundaries of the particle sections and applies different estimators depending on whether the segmentation was judged by a supervising expert to be satisfactory. If the segmentation is correct the estimate is computed automatically, otherwise the expert performs the necessary measurements manually. In case of convex particles we suggest to base the semiautomatic estimation on the so-called flower estimator, a new local stereological estimator of particle surface area. For convex particles, the estimator is equal to four times the area of the support set (flower set) of the particle transect. We study the statistical properties of the flower estimator and compare its performance to that of two discretizations of the flower estimator, namely the pivotal estimator and the surfactor. For ellipsoidal particles, it is shown that the flower estimator is equal to the pivotal estimator based on support function measurements along four perpendicular rays. This result makes the pivotal estimator a powerful approximation to the flower estimator. In a simulation study of prolate and oblate ellipsoidal particles, the surfactor also performs well for particles which are not extremely elongated. In particular, the surfactor is not very much affected by the singularity in the surfactor formula or by possible inaccuracies in the necessary angle measurements. We also assess the performance of the semiautomatic procedure in a study of somatostatin positive inhibitory interneurons from mice hippocampi. Only 35% of the cells needed to be analysed manually and an important decrease in workload was obtained by using the semiautomatic approach.

Orientational changes and impaired internalization of ellipsoidal nanoparticles by vesicle membranes

Wrapping and internalization of nanoparticles by biomembranes play a critical role in drug delivery applications and nanomedicine. We study the wrapping process of a vesicle membrane around spherical and ellipsoidal nanoparticles via minimization of the bending and adhesion energies. We report two distinct regimes of spreading and internalization separated by an energy barrier and relate the success or failure of the internalization to the particle shape and wrapping orientation. We predict more difficult internalization for ellipsoidal particles with higher aspect ratios. Wrapping of ellipsoidal particles is associated with an orientational change of the particle. While the spreading starts on the flat side of the ellipsoidal particle, the particle changes its orientation during wrapping and the internalization is achieved in the tip orientation of both prolate and oblate ellipsoidal particles.

Orientation, distribution, and deposition of elongated, inertial fibers in turbulent channel flow

In this paper, the dispersion of rigid, highly elongated fibers in a turbulent channel flow is investigated. Fibers are treated as prolate ellipsoidal particles which move according to their inertia and to hydrodynamic drag and rotate according to hydrodynamic torques. The orientational behavior of fibers is examined together with their preferential distribution, near-wall accumulation, and wall deposition: all these phenomena are interpreted in connection with turbulence dynamics near the wall. In this work a wide range of fiber classes, characterized by different elongation (quantified by the fiber aspect ratio, λ) and different inertia (quantified by a suitably defined fiber response time, τp) is considered. A parametric study in the (λ,τp)-space confirms that, in the vicinity of the wall, fibers tend to align with the mean streamwise flow direction. However, this aligned configuration is unstable, particularly for higher inertia of the fiber, and can be maintained for rather short times before fibers are set into rotation in the vertical plane. A more complex situation is observed in the spanwise and wall-normal flow directions, where fiber inertia and elongation destabilize near-wall alignment in a nontrivial fashion. Fiber orientational behavior and fiber translational behavior are observed to influence the process of fiber accumulation at the wall. Comparing the behavior of fibers with that of spherical particles, it is observed that the aspect ratio has little or no effect on clustering, preferential distribution, and segregation; yet it does affect the wallward drift velocity of the fibers in such a way that longer fibers tend to deposit at higher rates. No preferential orientation and no significant segregation is observed in the channel centerline, confirming that the role of inertia and, in particular, of elongation becomes less important in and beyond the logarithmic layer.