Non-spherical Particles Research Articles

Cuboids Prevail When Unraveling the Influence of Microchip Geometry on Macrophage Interactions and Metabolic Responses.

Drug delivery advances rely on using nano- and microsized carriers to transfer therapeutic molecules, although challenges persist in increasing the availability of new and even approved pharmaceutical products. Particle shape, a critical determinant in how these carriers distribute within the body after administration, raises opportunities of using, for instance, micrometer-sized nonspherical particles for vascular targeting and thereby creating new prospects for precise drug delivery to specific targeted areas. The versatility of polycrystalline silicon microfabrication allows for significant variation in the size and shape of microchips, and so, in the current work, photolithography was employed to create differently shaped polysilicon microchips, including cuboids, cubes, bars, and cylinders, to explore the influence of particle shape on cellular interactions. These microchips with different shapes and lateral dimensions, accounting for surface areas in the range of ca. 15 to 120 μm2 and corresponding total volumes of 0.4 to 27 μm3, serve as ideal models for investigating their interactions with macrophages with diameters of ca. 20 μm. Side-scattering imaging flow cytometry was employed for studying the interaction of label-free prepared microchips with RAW 264.7 macrophages. Using a dose of 3 microchips per cell, results show that cuboids exhibit the highest cellular association (ca. 25%) and uptake (ca. 20%), suggesting their potential as efficient carriers for targeted drug delivery to macrophages. Conversely, similarly sized cylinders and bar-shaped microchips exhibit lower uptakes of about 8% and about 6%, respectively, indicating potential benefits in evading macrophage recognition. On average, 1-1.5 microchips were internalized, and ca. 1 microchip was surface-bound per cell, with cuboids showing the higher values overall. Macrophages respond to microchips by increasing their metabolic activity and releasing low levels of intracellular enzymes, indicating reduced toxicity. Interestingly, increasing the particle dose enhances macrophage metabolic activity without significantly affecting enzyme release.

Expanding density-correlation machine learning representations for anisotropic coarse-grained particles.

Physics-based, atom-centered machine learning (ML) representations have been instrumental to the effective integration of ML within the atomistic simulation community. Many of these representations build off the idea of atoms as having spherical, or isotropic, interactions. In many communities, there is often a need to represent groups of atoms, either to increase the computational efficiency of simulation via coarse-graining or to understand molecular influences on system behavior. In such cases, atom-centered representations will have limited utility, as groups of atoms may not be well-approximated as spheres. In this work, we extend the popular Smooth Overlap of Atomic Positions (SOAP) ML representation for systems consisting of non-spherical anisotropic particles or clusters of atoms. We show the power of this anisotropic extension of SOAP, which we deem AniSOAP, in accurately characterizing liquid crystal systems and predicting the energetics of Gay-Berne ellipsoids and coarse-grained benzene crystals. With our study of these prototypical anisotropic systems, we derive fundamental insights on how molecular shape influences mesoscale behavior and explain how to reincorporate important atom-atom interactions typically not captured by coarse-grained models. Moving forward, we propose AniSOAP as a flexible, unified framework for coarse-graining in complex, multiscale simulation.

Transport of nonspherical particles in non-Newtonian fluid: A review

The transport of spherical particles in microchannel flow has been extensively studied owing to its relevance to efficient particle control, particularly in high-throughput cytometry and in single-cell detection and analysis. Despite significant advances in the field of inertial microfluidics, however, there remains a need for a deeper understanding of the migration of nonspherical particles in non-Newtonian fluids, given the diverse shapes of particles found in biological and industrial contexts. In this review, the transport behaviors of both spherical and nonspherical particles in both Newtonian and non-Newtonian fluids are examined. The current state of knowledge, challenges, and potential opportunities in inertial microfluidics are analyzed, with a focus on the underlying physical mechanisms and the development of novel channel designs. The findings presented here will enhance our understanding of the accumulation behavior of rigid particles in non-Newtonian fluid channel flow and may provide insights into efficient particle focusing and control in microfluidic devices.

Lattice Boltzmann method/computational fluid dynamics-discrete element method applications for transport and packing of non-spherical particles during geo-energy explorations: A review

Understanding the behavior of dispersed particles in subsurface porous media is essential for studying many transport phenomena in geo-energy exploration. Relevant phenomena include fluid transport through rock matrices, undesirable production of formation sands, colloid migration, circulation of drilling cuttings, and displacement of proppants in hydraulic fractures. The discrete element method (DEM), when coupled with the lattice Boltzmann method (LBM) and computational fluid dynamics (CFD), represents a useful numerical approach to studying these microscopic processes. This integrated approach allows for detailed modeling of particle–fluid and particle–particle interactions, which is particularly useful in dealing with particles with non-spherical shapes. This review focuses on recent advancements in DEM implementations for such particles and their coupling schemes with LBM and CFD numerical tools. It aims to assist scholars and practitioners in selecting the most effective LBM/CFD-DEM strategy for studying particle transport and packing in geo-energy scenarios. Although tailored for geophysical flows, the methodologies and analytical frameworks presented here also apply to fundamental investigations of particle-laden flows.

Light Scattering Measurements of KCl Particles as an Exoplanet Cloud Analog

Salt clouds are predicted to be common on warm exoplanets, but their optical properties are uncertain. The Exoplanet Cloud Ensemble Scattering System (ExCESS), a new apparatus to measure the scattering intensity and degree of linear polarization for an ensemble of particles, is introduced here and used to study the light scattering properties of KCl cloud analogs. ExCESS illuminates particles with a polarized laser beam (532 nm) and uses a photomultiplier tube detector to sweep the plane of illumination. Scattering measurements for KCl particles were collected for three size distributions representative of modeled clouds for the warm exoplanet GJ 1214b. Our measurements show that Lorenz–Mie calculations, commonly used to estimate the light scattering properties of assumedly spherical cloud particles, offer an inaccurate depiction of cubic and cuboid KCl particles. All of our measurements indicate that Lorenz–Mie scattering overestimates the backscattering intensity of our cloud analogs and incorrectly predicts the scattering at mid-phase angles (∼90°) and the preferential polarization state of KCl scattered light. Our results align with the general scattering properties of nonspherical particles and underscore the importance of further understanding the effects that such particles will have on radiative transfer models of exoplanet atmospheres and reflected light observations of exoplanets by the upcoming Nancy Grace Roman Space Telescope and Habitable Worlds Observatory.

Evident structural anisotropies arising from near-zero particle asphericity in granular spherocylinder packings.

With magnetic resonance imaging experiments, we study packings of granular spherocylinders with merely 2% asphericity. Evident structural anisotropies across all length scales are identified. Most interestingly, the global nematic order decreases with increasing packing fraction, while the local contact anisotropy shows an opposing trend. We attribute this counterintuitive phenomenon to a competition between gravity-driven ordering aided by frictional contacts and a geometric frustration effect at the marginally jammed state. It is also surprising to notice that such slight particle asphericity can trigger non-negligible correlations between contact-level and mesoscale structures, manifested in drastically different nonaffine structural rearrangements upon compaction from that of granular spheres. These observations can help improve statistical mechanical models for the orientational order transformation of nonspherical granular particle packings, which involves complex interplays between particle shape, frictional contacts, and external force field.

An integrated model for flexible simulation of biomass combustion in a travelling grate-fired boiler

Grate-fired boiler is of considerable interest for burning biomass owing to its reduced sensitivity to variations in fuel composition and size. However, grate-fired technology exhibits unsatisfactory performance in terms of combustion efficiency, contaminant emissions, and flame stability. CFD modelling can provide reasonable optimizations to overcome these drawbacks and ultimately achieve clean and efficient energy production. Conventional approach simulates the fuel-bed and freeboard combustion separately using an in- and over-bed coupling procedure, where data of the gases leaving from the packed-bed top and the radiative heat flux emitted by the high-temperature flame onto the bed cannot be interacted in real-time. This may cause distinct deviations in the calculations. In this paper, a three-dimensional (3D) full-scale integrated model is developed for the simulation of grate-fired boiler, in which the intensive combustion of both the freeboard and fuel-bed is solved in one scheme using the Eulerian-Lagrangian method. The gas phase is considered as a continuous medium and calculated by the Eulerian model, while the solid particles are considered as a discrete phase and tracked via the Lagrangian method. The reliability of the model is well verified through various field measurements and observations. Results shows that the key parameters are non-uniformly distributed along the grate width, i.e., the aerodynamic and combustion environment is poor at the vicinity of water-cooled walls compared with that at the furnace center. This results in a significant lag in volatile gases release and char oxidation near the water-cooled wall on both sides, which finally causes obvious differences in the distribution of temperature and species. For instance, the peak of CO concentration at the center is 12.6 % at 3.3m from the feed entrance, while that near the water-cooled wall is 8.6 % around 3.5m. The char burnout ratio in the bottom ash can be accurately calculated by this model, with a negligible relative error between the simulation of 81.97 % and the measurement of 82.50 %. It also provides a novel method for the calculation of fly ash particles by using size-grouped and non-spherical particles. Small-size particles in the vicinity of the feed inlet, as well as a part of the particles burning at the end of the grate are entrained into the freeboard by the primary air supplied beneath the grate and the high-momentum secondary air on the bed top. This model can provide valuable theoretical guidance for optimizing the refined distribution of fuel and air in grate-fired power plants and mitigating irregular deposition (corrosion) on heat exchangers and water-cooled walls caused by fly ash.

Combined thermal and particle shape effects on powder spreading in additive manufacturing via discrete element simulations

The thermal and mechanical behaviors of powders are crucial for additive manufacturing. In powder bed fusion, capturing temperature profiles and packing structures before melting is challenging due to diverse heat transfer pathways and powder properties. This study tackles this challenge with a discrete element model simulating non-spherical particles with thermal properties during powder spreading. Thermal conduction and radiation are integrated into a multisphere particle formulation to model heat transfer among irregular-shaped powders with temperature-dependent elastic properties. The model is utilized to simulate the spreading of pre-heated PA12 powder over a hot substrate representing the part under manufacturing. Variances in temperature profiles are observed in the spreading cases based on particle shapes, spreading speed, and temperature-dependent elastic modulus. Particle temperature beneath the spreading blade is influenced by the kinematics of the particle heap and temperature-dependent properties.

Polarization characterization of a nonspherical sea salt aerosol model

The T-matrix method was utilized to study the polarization characteristics of nonspherical sea salt aerosol models within the wavelength range of 0.48–2.5 µm. Analysis was conducted on the polarization characteristics of nonspherical sea salt aerosols across different wavelengths as a function of scattering angle. This included scrutinizing linear depolarization ratios under typical visible and near-infrared wavelengths for various aspect ratios. The impact of particle nonsphericity on the linear depolarization ratios of monodisperse and polydisperse sea salt aerosol particles was examined. The results indicate: (1) In the analysis of the polarization characteristics of sea salt aerosols, the trends of polarization properties are similar between monodisperse and polydisperse systems. The scattering phase function P11(θ) is predominantly more significant in the forward-scattering direction. P11(θ) is insensitive to wavelength changes in the backward-scattering direction. P33(θ)/P11(θ) varies across different bands; in the visible light spectrum, there are significant fluctuating changes, while in the infrared spectrum, it trends towards nearly linear changes. The variation trends of −P12(θ)/P11(θ) and P34(θ)/P11(θ) with scattering angle are similar, and both are significantly affected by changes in wavelength. (2) Regarding the depolarization ratio of sea salt aerosols, the value for polydisperse systems is more than twice that of monodisperse systems, and the greater the nonsphericity, the higher the linear depolarization ratio. In monodisperse systems, at a wavelength of 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 118.82, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum depolarization ratio is near 97.52; under polydisperse conditions, at 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 117.18, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum linear depolarization ratio is near 215.66. Investigating the polarization characteristics and linear depolarization ratios of nonspherical spheroid sea salt aerosol particle models at all scattering angles is important for remote-sensing detection, high-precision calibration, and other optoelectronic applications.

Collective dynamics and pair-distribution function of active Brownian ellipsoids in two spatial dimensions

While the collective dynamics of spherical active Brownian particles is relatively well understood by now, the much more complex dynamics of nonspherical active particles still raises interesting open questions. Previous work has shown that the dynamics of rod-like or ellipsoidal active particles can differ significantly from that of spherical ones. Here, we obtain the full state diagram of active Brownian ellipsoids in two spatial dimensions without hydrodynamic interactions depending on the Péclet number and packing density via computer simulations. The system is found to exhibit a rich state behavior that includes cluster formation, local polar order, polar flocks, and disordered states. Moreover, we obtain numerical results and an analytical representation for the pair-distribution function of active ellipsoids. This function provides useful quantitative insights into the collective behavior of active particles with lower symmetry and has potential applications in the development of predictive theoretical models.

Influence of Rolling Resistance and Particle Size Distribution in the Simulation of Sand Infiltration into the Static Gravel Bed

Fine sediment infiltration and subsequent clogging in a gravel bed affect several fluvial, ecological, and biological processes, resulting in the degradation of the river ecosystem. Despite many experimental and a few numerical studies, the process is yet to be entirely understood. We employed a pure Lagrangian framework, called the Discrete Element Method (DEM), to numerically investigate the infiltration process. Special attention is given to tackling the issue of non-spherical and irregular particle shapes and particle size distributions (PSDs) in numerical simulations. Due to computational limitations, these aspects were either not considered or simplified in previous numerical studies. We implicitly included non-spherical and irregular shape effects through rolling resistance models, which do not cause excessive computational overhead. Our study shows that rolling resistance models greatly influence packing and fine sediment infiltration. However, they may also lead to unphysical particle behavior; thus, they should be carefully used in numerical simulations. Oversimplified PSDs do not mirror natural systems, and full PSDs pose computational challenges. Sufficient grain classes are needed to mimic the non-homogeneity and poly-dispersity found in natural fluvial sediments. The infiltrating characteristics of sand concerning PSD and shape effects are linked to size ratio D15,Gravel/D85,Sand, assuring physical and realistic modeling of the infiltration process.

Viscosity prediction for dense suspensions of non-spherical particles based on CFD-DEM simulations

Reliable estimation of the viscosity and rheology of dense suspensions formed from non-spherical particles is of high importance for studies of many natural and industrial processes. Still, the complexity of underlying physics makes predicting the viscosity of such suspensions a challenging task, resulting in a lack of models capable of doing so for general suspensions. In this work, we present an approach based on a combination of the computational fluid dynamics (CFD) and discrete element method (DEM) developed for arbitrarily shaped particles and use it to predict viscosity of dense suspensions of spheres, rods, and glitters. Simulation results are compared to available experimental data and commonly used engineering correlations. The developed model can reliably predict suspension viscosity in a wide range of solid volume fractions and particle shapes. The simulations with spherical particles also reveal a shear-thickening trend at increased shear rates, which corresponds to the experimentally observed non-Newtonian behavior.

A direct particle tracking model for predicting homogeneous precipitation kinetics in Al-Sc alloys

The Kampmann-Wagner numerical (KWN) model, although been widely used in modeling the precipitation kinetics in solid solution alloys, has its own deficiency which is mainly reflected in two aspects: inability to track the growth history of individual particles and difficulty in describing the precipitation kinetics of non-spherical particles. In this work a direct particle tracking (DPT) model, which can well handle such issues, has been proposed and implemented. The main aim of this work is to check the validity and accuracy of the DPT model. To this end, the DPT model and two KWN models with different levels of accuracy have been applied to simulate the precipitation kinetics in two Al-Sc alloys. By comparing the numerical results with literature experimental data, it is found that the DPT model can well describe the microstructure evolutions during ageing of the Al-Sc alloys, and it has nearly the same accuracy as the KWN model with the governing equation solved by the high-resolution scheme (HR-KWN model). To reduce the amplitude of the oscillations formed in the particle size distribution (PSD) curves predicted by the DPT model, we need to set a small enough value for the time intervals divided in the nucleation stage.

On The Preparation Of Training Data For 3D Tracking Of Position And Orientation Of Microswimmers Using Defocusing And Deep Learning

The use of image analysis algorithms based on deep convolutional neural networks (CNNs) is opening new possibilities in experimental techniques for fluid dynamics. In the field of microscopic 3D particle tracking based on defocusing, it has been shown on synthetic images that CNNs can be used to determine not only the depth position but also the orientation of non-spherical microscopic particles or specimens. However, the translation of such approaches to experimental setups is challenging, especially due to the difficulty of obtaining reliable labeled images to train the neural networks. In this work, we propose a method to obtain labeled images of microswimmers from conventional microscopy images, exploiting the properties of the swimming motion at low Reynolds numbers, where inertial effects are negligible. This method allows us to obtain ground truth values of orientation and depth position of a microorganism swimming at a regular pace that can be used as training data for CNNs. The proposed methodology was used to obtain labeled images from experimental videos of the micro-organism Euplotes Vannus. The labeled images were used to train a VGG16 network, providing an estimated uncertainty in the determination of the orientation angles psi, theta, phi, and the depth position Z of 2.4%, 1.4%, 2.3%, and 3.5%, respectively.

Updating the Loth Drag Model to Include Nonspherical Particle Effects

Sophisticated drag models have been developed over the past few decades that are based on ballistic range and other experimental data. These drag models are applicable over a wide range of particle-flow environments and include compressibility and rarefaction effects. One drawback of these sophisticated drag models is that they assume spherical particles. However, Martian dust particles and materials used in ground-based dusty-flow experiments such as Al2O3 or BN are known to be nonspherical. It is well known that nonspherical particles, in general, will experience higher drag forces compared to spherical particles. There has also been a considerable amount of research developing drag models that account for nonspherical particle shapes, but most of these models are restricted to incompressible, continuum particle-flow conditions. This paper presents a simple way to include nonspherical particle effects into the widely used Loth particle drag model. This updated drag model is used to simulate dust-laden flow experiments performed in the German Aerospace Center the multiple phase flow facility (GBK) experimental facility and in the shock layer of a Martian-entry spacecraft to assess the effectiveness and range of applicability of this new drag model. In the GBK experiment simulations, the modified Loth drag model, which includes both compressibility and nonspherical particle effects, showed improved comparison to the experimental data.

Influence of WC particle size and morphology on the performance of NiCu-based composite coatings deposited by laser direct energy deposition

NiCu alloys are commonly utilized due to their outstanding plasticity, toughness, corrosion resistance, and thermal conductivity. Nevertheless, their limited hardness and wear resistance have hindered their further development. In this study, 24CrNiMo alloy brake disc was coated with NiCu-based composite coatings containing different sizes and shapes of tungsten carbide, in order to investigate the effects of tungsten carbide particle characteristics on the microstructure, microhardness and wear resistance of Nickel‑copper composite coating. The results show that the microstructure of the coatings was minimally affected by the size and morphology of the WC particles, while non-spherical WC particles exhibited superior uniformity within the coatings. In terms of microhardness, smaller WC particles demonstrated a more consistent distribution. The ball-disk wear tests revealed that coatings with larger WC particles displayed better wear resistance in sizes, while those with non-spherical WC particles exhibited excellent resistance to wear in morphologies. Additionally, in abrasive wear tests, composite coatings containing spherical WC particles demonstrated superior wear resistance compared to those containing non-spherical WC particles. The diverse wear resistance observed in different wear experiments among the various WC coatings can be attributed primarily to differences in the distribution and preparation methods of the WC particles. Consequently, these findings hold significant promise for the practical application of NiCu-based composite coatings in industry.

Experimental study on the combined influence of particle shape, density, and size on segregation behavior in binary and ternary granular mixtures

Segregation of granular materials is a common experience; however, a few studies consider the segregation of granular mixtures characterized by variations in particle shape. Additionally, many particle systems in industry and geophysics consist of nonspherical particles. In the present study, we conducted a series of experiments to investigate the influence of particle shape, density, and size on the dynamic characteristics and segregation behavior in binary and ternary granular mixtures. Our experimental findings demonstrated a noteworthy correlation between the final steady-state segregation intensity and the proportion of non-spherical beans and cube-shaped particles in a ternary granular mixture. Specifically, the presence of beans, which are larger than the other particles, in a binary and ternary granular mixture increased the size-induced segregation phenomenon. Conversely, the steady-state segregation intensity decreased as the proportion of cube particles, which were less dense but of the same volume as the other materials, increased in a ternary granular mixture, indicating a mitigation of density-induced segregation. The study also discusses the relationship among the dynamic angle of repose, dynamic properties, and segregation behavior arising from the effects of shape, size, and density in binary and ternary granular mixtures.

Drag, lift, and torque correlations for axi-symmetric rod-like non-spherical particles in linear wall-bounded shear flow

This paper presents novel correlations to predict the drag, lift, and torque coefficients of axi-symmetric non-spherical rod-like particles in a wall-bounded linear shear flow. The particle position and orientation relative to the wall are varied to systematically investigate the influence of the wall on the hydrodynamic forces. The newly derived correlations for drag, lift, and torque on the particle depend on various parameters, including the particle Reynolds number, the orientation angle between the major axis of the particle and the main local flow direction, the aspect ratio of the particle, and the dimensionless distance from the particle centre to the wall. The impact of the wall on the hydrodynamic forces is accounted for as a function of a multiplication factor on the drag force in case of locally uniform flow, and an additional force contribution for the lift and the torque, modifying the resultant forces experienced by a particle in a locally uniform flow. The changes in the hydrodynamic forces prove to be substantial, emphasizing the necessity of accounting for wall effects across all particle types and flow conditions investigated in this study. The coefficients of the correlations are determined through a fitting process utilizing the data generated from our previous study on the interaction forces between a locally uniform flow and an axi-symmetric non-spherical rod-like particles, as well as from data of novel direct numerical simulations (DNS) performed in this work of flow past axi-symmetric rod-like particles near a wall. The proposed correlations exhibit a good agreement compared to the DNS results, with median errors of 2.89%, 5.37%, and 11.00%, and correlation coefficients of 0.99, 0.99, and 0.96 for the correlations accounting for the drag, lift, and torque coefficients of a non-spherical particle in wall-bounded linear shear flow profile, respectively. These correlations can be used in large-scale simulations using an Eulerian–Lagrangian or a CFD/DEM framework to predict the behaviour of axi-symmetric rod-like non-spherical particles in wall-bounded shear flow to locally uniform flow conditions.

Experimental investigation of pressure drop of spherical and non-spherical coarse particles in pneumatic conveying in horizontal pipes

In this work, the conveying flow pattern and pressure drop of spherical and non-spherical coarse particles in a horizontal pipe were measured experimentally. The experimental results show that when coarse particles are conveyed in stratified flow and sedimentation and dune formation, the rate of increase of pressure drop with superficial velocity is related only to the particles and not to the conveying conditions. The rate of increase of pressure drop with velocity is larger for spherical particles than for non-spherical particles in stratified flow, and the rate is smaller for spherical particles than for non-spherical particles in sedimentation and dune formation. The pressure drop varies linearly with the solid-gas ratio, and the slope of the linear relationship characterises the friction of the conveying pipe and the interaction parameters between the particles. The reduction in pressure drop for spherical particles is greater than that for non-spherical particles when the solid-gas ratio is increased by the same magnitude. In addition, to verify the experimental results of this work the data cited in the published literature were compared and the results were in good agreement. On the one hand, the variation rule of pressure drop with superficial velocity obtained in this investigation is an enrichment of the classical phase diagram. On the other hand, the experimental results are of guiding significance for the design and engineering application of coarse particle pneumatic conveying systems.

Depth from Defocus technique for irregular particle images

The Depth from Defocus (DFD) imaging technique for measuring the size and number concentration of particles in dispersed two-phase flows has up to now been restricted to the processing of spherical particle images. This study examines how this technique can be extended to process irregular particle images, arising either from neighboring spherical particles which lead to overlapping images, or from the imaging of non-spherical particles. In either case, the application scope of the DFD technique is significantly expanded. On the one hand the ability to identify and process overlapping images allows measurements to be performed at higher number/volume concentrations. On the other hand, especially solid particles are often non-spherical, thus making the DFD technique attractive for these applications. For both cases, the processing algorithms are experimentally benchmarked against ground truth using a dedicated apparatus in which particles of known size, shape and degree of overlapping images can be systematically varied.