Non-spherical Particles Research Articles

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.

Influence of normal force on magnetic-field-induced shear modulus of isotropic and anisotropic magnetorheological elastomers having spherical and non-spherical shape iron particles

ABSTRACT Isotropic and anisotropic magnetorheological elastomers (MRE) were prepared using spherical carbonyl iron (CI) particles and electrolyte non-spherical iron (EI) particles having a 60% weight fraction in silicon rubber. The pre-structured MREs were prepared under a constant magnetic field of 0.3 Tesla. A parallel-plate MR rheometer with a magneto-rheological cell was used to conduct dynamic measurements under different normal forces. All the data were recorded under 1 Hz frequency and strain amplitude of 0.1% (in the linear viscoelastic region), and normal force was varied from 1N to 10 N. Results show that the magnetic-induced shear modulus increases in both MREs with normal force for isotropic as well as anisotropic samples. However, in CIP-based MRE, the MR effect increases with a pre-structured sample, whereas for EIP-based pre-structured MRE, the MR effect decreases compared to isotropic samples. Nevertheless, the relative MR (RMR) effect decreases with normal force in both cases. The rate of decrease is different in CIP- and EIP-based MREs. A possible mechanism for the same is discussed in the paper.

Investigating the influence of design parameters on the flow characteristics of a rectangular gas-solid fluidized bed with non-spherical particles

Investigating the influence of design parameters on the flow characteristics of a rectangular gas-solid fluidized bed with non-spherical particles

Discharge of rice-shaped particles from a monolayer flat-bottom silo.

In this work, we performed experiments regarding the outflow of spheres and two different types of rice-shaped particles in a quasi-two-dimensional monolayer silo with a flat bottom. We investigate the velocity and solid fraction profiles at the orifice and test whether the profiles for nonspherical particles have similar self-similar properties as in the spherical case. We find that the magnitude and shape of the velocity profiles for all three particle types are in a similar range. In contrast, the solid fraction at the orifice has a dome-shaped profile for both rice particles, whereas the profile for spherical particles is rather flat. The discharge rate determined from the velocity and solid fraction profiles describes the independently measured experimental discharge rate very well for all three investigated particle types.

Investigation of the Dominant Effects of Non-Spherical Particles on Particle–Wall Collisions

A deep understanding of the particle–wall collision (PWC) behaviors of non-spherical particles is important for managing gas–solid flows in industrial applications. It is important to identify the dominant parameters and to develop the common PWC prediction models for typical non-spherical particles. In this paper, different types of non-spherical particles were used to conduct the fundamental experiments. The effects of key parameters such as particle size, non-sphericity, wall roughness, and impact angle were analyzed. The results show that the trends of the collision coefficients with the impact angle for all non-spherical particles are similar. The dominant factors of particle–wall collisions are particle sphericity and wall roughness. A model with four parameters was fitted from the experimental data. The model can predict the collisions of non-spherical particles on rough steel walls with sizes ranging from 50 to 550 microns.

Particle and bulk media characteristics of food waste compost-based biomedia by dynamic high-temperature aerobic composting process

The dynamic high-temperature aerobic composting (DHAC) process, as a decentralized system, is considered a sustainable strategy for renewable resource-based raw materials. The food waste compost-based biomedia (BMFWCs) produced within five days of the DHAC process exhibited the physical properties of peaty topsoil with acceptable maturity under the meso-thermophilic phase. To understand the particle and bulk media characteristics of the BMFWCs, organic matter (OM) fraction–density–porosity parameters, particle size distribution, and uniformity coefficient were considered. Operating the DHAC process produced end products characteristics of relatively high total porosity (φb,T) and low dry bulk density (ρb) compared to the conservative mixture theory due to binary mixing and shape effects. A significant change in total porosity was estimated as an increase in non-spherical fibrous particles within the OM fraction of 0.4. Appropriate organic–mineral additives led to the effective arrangement of the variable porosity structure and improvement of aggregate stability (fom,spent coffee grounds≥0.2, fm,oyster shell powder≤0.4). The Forced aeration supply contributed to the expansion of the open space and macropore structures that serve as gas passages in the BMFWCs, while the introduction of microbes (Bacillus subtilis) promoted the biodegradation of medium and small macroaggregates (0.25–2 mm). The BMFWCs produced by the DHAC process was expected to have application potential in sustainable nature-based solution technology, due to appropriate particle properties, uniformity, and maturity.

A new discrete element method for small adhesive non-spherical particles

Small adhesive particles with non-spherical shapes are common in natural and industrial processes. However, it is challenging to accurately simulate the dynamic behaviors of non-spherical particulate systems, not only due to the complex local geometry at the contact region but also to the non-linear coupling between the van der Waals adhesion and the elastic deformation. In this paper, we develop a discrete element method (DEM) framework for small non-spherical particles. Particularly, we present a simple algorithm for solving the implicit equations of the dimensionless generalized JKR model, to accurately resolve the local surface geometry at the contact region and the strong coupling between the elastic deformation and the surface adhesion. New explicit expressions are established for the pull-off force, overlap and minor-to-major ratio of the contact ellipse, to naturally capture the pull-off point upon collision. Then the actual contact parameters including the contact radius, curvatures and overlap are used to modify the interparticle interactions, including the normal elastic-adhesive-dissipative force and sliding-rolling-twisting resistances. Finally, the framework is quantitatively validated by four random packing problems, including adhesive spheres, ellipsoids, spherocylinders and dimers, and the representative non-adhesive ellipsoids. Both the microscopic and macroscopic properties of packings agree well with a large number of classic theories, experiments and simulations, showing the satisfactory accuracy and effectiveness. The newly developed adhesive DEM framework has the full capability to dynamically simulate the collision-related behaviors of complex shaped particles in the presence of van der Waals adhesion and frictional forces.

Electrical analysis and molecular dynamics of anion in ferroelastic [(CH3)4P]2CoBr4 crystal near high-temperature phase transitions

The recent technological advances require an aligned innovation in the materials used for the construction of electronic devices. Hybrid materials play a important role in the optoelectronic applications because they combine both the organic and inorganic components. To this end, the [(CH3)4P]2CoBr4 compound was successfully synthesized using the slow evaporation solution growth approach at room temperature. In-depth research has been conducted on the structural, morphological, vibrationnal and electrical characteristics. The [(CH3)4P]2CoBr4 compound crystallises in the monclinic system with P121/C1 space group. The examination of SEM images reveals that the majority of grains have an average size of around 4 μm with irregularly shaped and non-spherical particles. The measured Raman spectra demonstrate the coexistence of two transition phases located at 373 K and 428 K. In fact, these observations suggest that the anionic components play a significant role in influencing the phase transitions mechanism. Analysis of the complex impedance spectra reveals that the electrical characteristics of the material is strongly dependent on both frequency and temperature. That indicates the existence of a relaxation phenomenon and of a semiconductor-type behavior. One single semicircle is detectable in the Nyquist plots of the complex impedance spectra, which can be satisfactorily fitted with a combination of R//C//CPE elements assigned to the bulk response. Therefore, we can conclude from this behavior that the sample is electrically homogeneous. The dependency of s(T) on temperature also shows that the correlated barrier hopping and the non-overlapping small polar on tunneling model are the responsible mechanisms for the AC conduction in [(CH3)4P]2CoBr4.

The normal restitution coefficient and critical sticking velocity of disk-shaped adhesive particles

The particle-wall collision is an important phenomenon in gas-solid flows. For non-spherical particles like disk-shaped particles, the classic models based on quasi-spherical assumptions cannot be directly applied. It is still challenging to evaluate the loss of kinetic energy by resolving the adhesion and viscoelastic damping because of their strong coupling. To address this issue, we employ the finite element method (FEM) to conduct a numerical investigation of the particle-wall collision dynamics of adhesive, disk-shaped particles. The viscoelastic model and adhesion are coupled to naturally reproduce the energy dissipation. Our findings reveal that the non-spherical nature of the particles influences energy dissipation through two distinct mechanisms: viscoelastic dissipation by changing the collision time and adhesion by changing the contact area. Explicit expressions of the restitution and the critical sticking velocity of the disk-shaped particles are given, which can be directly used in the numerical simulation under the Euler-Lagrange framework.

CFD-DEM mixing of rod-like and spherical particles in fluidized beds

Understanding the behavior of particle mixing in fluidized beds is crucial for enhancing process design. This article focuses on investigating the effect of key parameters, such as volume fraction of spherical particles, length of rod-like particles, and aspect ratio of rod-like particles, on the mixing of binary mixtures containing spherical and rod-like particles. The study employs a computational approach which couples the computational fluid dynamics and discrete element method (CFD-DEM) to explore mixing behavior of particles. Non-spherical particles are modeled using the multi-sphere method. A combination of qualitative and quantitative approaches is employed to assess the mixing performance, including visual examination of the fluidized bed and calculation of the subdomain-based mixing index. It was shown that an increase in rod-like particle length, aspect ratio, and volume fraction of rod-like particles weaken the mixing. Furthermore, the quality of mixing is directly influenced by bubble size and particle granular temperature. This study offers valuable insights into the mixing behavior of rod-like and spherical particles, contributing to the design and optimization of binary fluidization processes.

Exploring the micro-to-macro response of granular soils with real particle shapes by way of μCT-aided DEM analyses

This contribution provides high-fidelity images of real granular materials with the aid of X-ray micro-computed tomography (μCT), and employs a multi-sphere representation to reconstruct non-spherical particles. Through discrete-element method (DEM) simulations of granular samples composed of these non-spherical clumps, the effect of particle shape on the macroscopic mechanical response and microscopic soil fabric evolution is examined for soil assemblies under triaxial compression. Simulation results indicate that materials with more irregular particles tend to show higher shear resistance in both peak and critical states, while exhibiting higher void ratio under isotropic loading conditions and in the critical state. The proposed critical state parameters for describing the sensitivity of the mean coordination number to confining pressures are larger as particles become more irregular. At a microscopic level of observation, directional and scalar parameters of particle contacts are sensitive to predefined particle shapes. More irregular materials appear to exhibit higher fabric anisotropy with respect to particle orientation in the critical state, while the branch vector is affected by both contact modes and particle shape. The critical stress ratio from the simulation results is validated by comparing with experimental results, and further found to be linearly linked to the shape-weighted fabric anisotropy indices.

Machine learning based tool for the efficient estimation of geometric features of aggregated aerosol particles

While significant progress has been made in developing models for the formation and transport of aerosol aggregates, there is still a need for a simple, versatile tool capable of estimating intrinsic properties of aggregated particles. Scalar friction factor is an important parameter used extensively in the field of aerosol science. The scalar friction factor for non-spherical particles can be computed with the information on two geometric parameters, hydrodynamic radius (Rh) and orientationally averaged projected area (PA), depending on the momentum transfer regime. Although the existing methods for the estimation of these descriptors are efficient, many applications involve frequent estimation of these geometric descriptors, which can be time-consuming. We propose a Machine Learning (ML) based tool that can predict these descriptors using Fractal Dimension, pre-exponential factor, number of monomers and anisotropy factors as the input. An extensive database comprising fractal parameters, anisotropy factors, Rh, and PA is developed for testing and training the ML models. Five ML methods were assessed, with random forest (RF) identified as the most effective. The RF model demonstrated high accuracy in the testing phase, with R-squared value of 0.9875 for Rh and 0.9979 for PA, and average errors of 3.17% and 1.21% for Rh and PA, respectively. The predicted Rh and PA values were then used to estimate other relevant 3-dimensional properties such as mobility diameter, shape factor, and aerodynamic diameter, with the results indicating high accuracy of the prediction tool. Python-based tool offers ease of use, and can be easily integrated with other numerical codes.

A light scattering model for large particles with surface roughness

A physical-optics hybrid method designed for the computation of single-scattering properties of particles with complex shapes, including surface roughness, is presented. The method applies geometric optics using a novel ray backtracing algorithm to compute the scattered field on the particle surface. A surface integral equation based on the equivalence theorem is used to compute the scattered far-field, which yields the full Mueller matrix and integrated single-scattering parameters. The accuracy is tested against the discrete dipole approximation for fixed orientation smooth and roughened compact hexagonal columns for 3 values of refractive index. The method is found to compute asymmetry parameter, and scattering and extinction efficiencies with mean errors of −1.0%, −1.4%, −1.2%, respectively, in a computation time reduced by 3 orders of magnitude. The work represents a key step forwards for modelling particles with physical surface roughness within the framework of physical-optics and provides a versatile tool for the fast and quantitative study of light scattering from non-spherical particles with size much larger than the wavelength.

Determination of interparticle radiative heat transfer and radiation absorption for ellipsoidal particle beds using Monte Carlo ray tracing

The calculation of radiative heat transfer between particles in particle-based solar systems presents significant challenges in terms of computational cost and accuracy. This study addresses these challenges by employing the discrete element method to generate random particle packings and the Monte Carlo ray tracing method to investigate the influence of particle shape and volume fraction (ϕ) on interparticle radiation transfer and the absorption of incident radiation. The results reveal that, at low volume fractions, the shape and orientation of ellipsoidal particles have a pronounced impact on direct radiative transfer. Oblate particles exhibit the highest average radiation distribution factor (RDF), and the dispersion of RDF data is more prominent for oblate and elongated prolate particles compared to spheres. As ϕ increases to 0.35, the contribution of indirect transfer from neighboring particles becomes significant for oblate particles, resulting in a reduction in the dispersion of RDF data. Furthermore, when ϕ reaches 0.55, the decisive factor in determining RDF becomes the shielding effect of particles positioned between the emitting and receiving particles. The average RDF tends to converge among particles of different shapes, although oblate and elongated prolate particles still exhibit considerably larger RDF dispersion compared to spherical and near-spherical particles. Additionally, the effective absorptivity of the particle bed for incident radiation decreases as the aspect ratio of particles increases at all volume fractions. Moreover, the transmitted fraction demonstrates an exponential relationship with the depth, and beds composed of spherical particles exhibit better radiation transmittance compared to beds containing non-spherical particles.

Simulation of 3D Volume Filling with Non-Spherical and Spherical Titanium Alloy Powder Particles for Additive Manufacturing

Simulation of 3D Volume Filling with Non-Spherical and Spherical Titanium Alloy Powder Particles for Additive Manufacturing

Enhanced fully resolved CFD-DEM-PBFM simulation of non-spherical particle–fluid interactions during hydraulic collection

The interactions between non-spherical particles and fluids are commonplace in both nature and engineering applications, such as deep-sea nodules hydraulic collection. However, accurately simulating granular particles with non-spherical shapes and gaining a deep understanding of the intricate mechanisms involved in fluid–particle interactions still pose significant challenges. In this study, the superquadric model and the Gaussian curvature model are introduced in the Discrete Element Method to describe particle shapes and characterize their nonlinear contact behavior, respectively. Simultaneously, the Fictitious Domain-Immersed Boundary Method (FD-IBM) and the Particle Boundary Field Method (PBFM) are employed to enhance the stability and accuracy of numerical simulations. Building upon these advancements, an extended resolved CFD-DEM-PBFM method is developed. The validation and superiority of this resolved CFD-DEM-PBFM method are rigorously verified by comparing its results with the experimental and other research results across various scenarios, including non-spherical particle collision and packing, particle settling, drafting-kissing-tumbling test, and flow around non-spherical particles. Subsequently, the application of our novel model has been further conducted by a case study that simulates the hydraulic collection of nodules with different aspect ratios l/d. Concurrently, the influences of the nodule shapes on the hydraulic collection mechanism of the hydraulic collection are unveiled in terms of suction forces, trajectory of the particle, and flow field characteristics. Our findings demonstrate that the extended resolved CFD-DEM-PBFM method excels at accurately characterizing multiphase interaction mechanisms at both macro and micro scales, presenting considerable advantages in simulating fluid-particle systems involving non-spherical particles.

Convective heat transfer into moving fluid from a heated prolate spheroid

A common assumption in heat transfer models that involve fluid-solid interactions is that solid particles have a spherical shape. However, in numerous engineering applications, it is crucial to gain insights into the heat transfer mechanisms involving non-spherical particles and flowing fluids. These processes often employ particles with altered shapes, such as elongated geometries resembling prolate spheroids.A numerical study of airflow past a stationary constrained prolate spheroid under forced convective heat transfer is performed. A large temperature difference of the spheroid's surface was maintained relative to free stream temperature. Navier-Stokes and energy equations were solved to investigate the impact of Reynolds number (Re) and aspect ratio (AR) on convective heat transfer rate and Nusselt number (Nu). We focus on a wide range of spheroids' surface temperatures up to 1500 K in our study, which has never been studied in depth before. The simulations show that the mean Nu has a positive dependence on Ts, AR, and Re.A new correlation has been introduced that calculates the average Nusselt number (Nu) for spheroidal particles without assuming an isothermal condition (where the surface temperature Ts is roughly equal to the ambient temperature T∞). The suggested correlation incorporates the influence of AR, surface temperature, and Re.

Spreading Behavior of Non-Spherical Particles with Reconstructed Shapes Using Discrete Element Method in Additive Manufacturing.

The spreading behavior of particles has a significant impact on the processing quality of additive manufacturing. Compared with spherical metal material, polymer particles are usually non-spherical in shape. However, the effects of particle shape and underlying mechanisms remain unclear. Here, the spreading process of particles with reconstructed shapes (non-spherical particles decomposed into several spherical shapes by stereo-lithography models) are simulated by integrating spherical particles with the discrete element method. The results show that more cavities form in the spreading beds of particles with reconstructed shapes than those of spheres with blade spreading. Correspondingly, particles with reconstructed shapes have lower packing densities, leading to more uniform packing patterns. Slow propagation speeds of velocity and angular velocity lead to "right-upwards" turning boundaries for particles with reconstructed shapes and "right-downwards" turning boundaries for spherical particles. Moreover, as the blade velocity increases, the packing density decreases. Our calculation results verify each other and are in good agreement with the experiment, providing more details of the behavior of non-spherical particles before additive manufacturing. The comprehensive comparison between polymer non-spherical particles and spherical particles helps develop a reasonable map for the appropriate choice of operating parameters in real processes.

Measuring Spherical and Nonspherical Binary Particles: Mixing and Segregation in a Rotating Drum Using Machine Learning-Assisted Image Processing

Measuring Spherical and Nonspherical Binary Particles: Mixing and Segregation in a Rotating Drum Using Machine Learning-Assisted Image Processing

Numerical investigation of collision characteristics of non-spherical particles on ductile surfaces under normal impact

Numerical investigation of collision characteristics of non-spherical particles on ductile surfaces under normal impact