Cylindrical Particles Research Articles

Numerical Analysis for Thermal Performance of a Photovoltaic Thermal Solar Collector with SiO2-Water Nanofluid

Numerical analysis of a photovoltaic-thermal (PV/T) unit with SiO 2 -water nanofluid was performed. The coupled heat conduction equations within the layers and convective heat transfer equations within the channel of the module were solved by using the finite volume method. Effects of various particle shapes, solid volume fractions, water inlet temperature, solar irradiation and wind speed on the thermal and PV efficiency of the unit were analyzed. Correlation for the efficiencies were obtained by using radial basis function neural networks. Cylindrical shape particles were found to give best performance in terms of efficiency enhancements. Total efficiency enhances by about 7.39% at the highest volume fraction with cylindrical shape particles. Cylindrical shape particle gives 3.95% more enhancement as compared to spherical ones for the highest value of solid particle volume fraction. Thermal and total efficiency enhance for higher values of solid particle volume fraction, solar irradiation and lower values of convective heat transfer coefficient and inlet temperature. The performance characteristics of solar PV-thermal unit with radial basis function artificial neural network are found to be in excellent agreement with the results obtained from computational fluid dynamics modeling.

Axial and radial patterns of a bidispersed suspension in a fully filled horizontal rotating cylinder

We report on the pattern formation in a horizontal rotating cylinder fully filled with bidispersed suspension composed of non-Brownian settling and floating particles. The effect of particle mixing of different buoyancy and shape on the axial and radial pattern formation was investigated using flow visualization and particle image velocimetry techniques. The experimental investigations involved two cases divided according to the shape of the particles making up the suspension. In the first case, both the floating and settling particles were spherical in shape while the second one was composed of buoyant spherical and settling cylindrical particles. A detailed analysis of the difference between the monodispersed and bidispersed suspension for various rotational speeds is provided. The radial and axial patterns for the bidispersed suspension was found to strongly depend on the rotation rate. The behavior at low rotation was similar to that of monodispersed systems, but at higher speeds, hybrid patterns emerged that were driven by the complementary influence of the two kinds of particles. The patterns observed were seen to be primarily influenced by the particle-particle hydrodynamic interaction. The nonspherical nature of the cylindrical particles produces radial and axial patterns that are distinctly different from the spherical particles.

Numerical investigations on random close packings of cylindrical particles with different aspect ratios

Random close packings (RCP) of different shaped cylindrical particles under optimal vibration conditions were numerically reproduced using discrete element method. Corresponding characteristic macro and micro properties such as packing density, coordination number (CN), radial distribution function (RDF), particle orientation, orientation randomness and forces/stresses as a function of particle aspect ratio (AR) were systematically characterized and analyzed. And the container wall effects on the packing were also comprehensively considered. The results show that with the increase of AR, the packing density of each RCP structure first increases to a maximum (0.70 with AR = 1) and then decreases. The RDF analysis shows the particle arrangement of local structure varies with AR. The container wall is only in effect within three layers for equiaxed cylinders (AR = 1) near the boundary and just one layer for other shaped cylinders. The non-equiaxed cylinders especially elongated ones exhibit a strong tendency to horizontal alignment. With the growth of AR, the nematic order parameter of the packings first decreases to a minimum and then increases. Both particle position and orientation distributions demonstrate that the obtained packing structures are random. Force analyses indicate that the strong forces follow an exponential distribution, while those weak forces follow a power-law distribution, which is comparable to the force distributions of spherical particles. Compared with other cylindrical particles, the force orientation distribution in the packing of equiaxed cylinders is more homogenous. The peak position of the hydrostatic stress distribution is the same for different shaped cylinders. Moreover, with the increase of the packing density, the percentage of strong stresses increases. With the AR deviating from 1, the static vertical stresses present a gradually larger saturation stress in the same depth.

Monte Carlo studies of optical transmission of anisotropic suspensions

Monte Carlo model for simulation of light transmission in anisotropic suspensions filled by absorbing cylindrical particles with anisotropic shape was developed. Aspect ratio of the cylinders (i.e., ratio of length and diameter) was varied between r = 0 (infinitely thin disks) and r → ∞ (infinitely thin rods). The cooperative filling model was used for simulation of clustering of particles controlled by aggregation parameter f. Orientation ordering of particles in anisotropic suspension was characterized by order parameters S. The effective cross section of particles and deviations from the Beer–Lambert–Bouguer law were studied as function of r, f and S. Obtained data may be useful for understanding the experimental data on optical properties of media filled with carbon nanotubes.

Size-dependent effects sensitively determine buckling of a cylindrical silicon electrode particle in a lithium-ion battery

The influence of size-dependent effects on mechanical behavior of a cylindrical silicon electrode particle within a lithium-ion battery is investigated, and it is shown that these effects sensitively determine critical buckling behavior. The mathematical framework used for this investigation incorporates the bond-order-length-strength (BOLS) theory correlation in a general finite deformation theory model that includes the two-way coupling between diffusion-induced stress and stress-influenced diffusion. Additionally, the possibility of plastic flow is accounted for in the model to allow probing situations with relatively high charging rates. Significant differences, arising due to the consideration of the size-dependent effects and captured through the BOLS theory, are highlighted. In particular, it is found that, in most cases studied, both stresses and plastic stretches are amplified in magnitude. Tensile to compressive stress reversal also takes place faster on considering the BOLS theory. The modeling framework is further applied to estimate critical lengths that are safe against buckling. Thus, it is expected that the presented framework will provide an improved aid for the design of nanowire-based lithium ion battery silicon electrodes.

Percolation probability in a system of cylindrical particles.

A broad variety of materials, ranging from composites and heat transfer nano-fluids to electrochemical energy storage electrodes, widely employ cylindrical particles of various aspect ratios, such as carbon nanotubes. These particles are generally excellent conductors of heat and electricity and when dispersed in a continuous medium influence dramatically the transport properties of the heterogeneous material by forming a percolating network. Numerous theories exist to predict key parameters such as particle concentration at the percolation threshold and transport properties at concentrations beyond the threshold. The microstructure formed by connecting particles in the material is an important determinant toward such parameters but often requires complex numerical models to resolve. In this paper, we present an analytical, probabilistic model capturing the microstructure of a system of randomly positioned, soft-core, cylindrical particles with a finite aspect ratio, valid at arbitrary particle concentration. Our analytical framework allows for the calculation of the particle contact number distribution and percolation probability of the particle system. We show that our analytical model is more accurate than excluded volume theory for predicting the percolation threshold for spherocylinders of finite aspect ratios, and agrees well with the corresponding numerical results. Our theory describes the percolating network topology above the percolation threshold and can serve as the foundation for analytical composition-structure-property relationships for heterogeneous materials with conducting cylindrical particles.

Effect of particle shape on catalyst deactivation using particle-resolved CFD simulations

A method has been demonstrated using particle-resolved CFD simulations to simulate the transient catalyst deactivation due to carbon formation process and its impact on the particle properties. Preliminary simulations with cylindrical particles and propane dehydrogenation reactions showed higher carbon accumulation for the near-wall particles due to the presence of wall heat flux. Significant gradients of carbon concentration within the particle pointed to the presence of diffusion limitations. The accumulated carbon decreased the rate of the reactions thereby decreased the propene formation with time. Later, the effect of particle shape on the catalyst deactivation was investigated using five different particle shapes with constant particle volume, but varying in particle surface area. Considerable variations in the accumulated carbon were observed both with respect to the particle position and the particle shapes. The initial reaction rate increased with the particle surface area due to reduced diffusion limitation, but after a certain time, it decreased with particle surface area due to faster catalyst deactivation. As a result, the propane conversion and propene yield decreased with particle surface area. Also, the propene yield to ΔP ratio decreased with particle surface area due to smaller ΔP offered by particles with the lower surface area. Therefore, the present work showed that the particles with the lower surface area are favorable for propane dehydrogenation process due to slower catalyst deactivation leading to higher conversion and longer operating time. The trilobe particle shape gave the highest propane conversion and highest propene yield to ΔP ratio.

Simulation of flow in granular porous media using combined Lattice Boltzmann Method and Smoothed Profile Method

Lattice Boltzmann Method (LBM) is used for simulation of fluid flow in three-dimensional porous media composed of spherical or cylindrical particles. The solid-fluid interaction is modeled based on the Smoothed Profile Method (SPM) and a GPU parallelized CUDA code is employed for this study to reduce the computational time. The effect of porosity, size and shape of particles, and the structure of porous media on the permeability as well as the drag coefficient is investigated. Results show that the SPM-LBM method is accurate in terms of the determination of drag force. A comparative study performed between analytical solutions and the proposed method for simulating fluid flow in the porous medium shows that the LBM-SPM can accurately predict the permeability in porous media formed from spherical or cylindrical particles. In addition, the SPM-LBM shows more accurate results and less dependency on viscosity in comparison to the bounce-back scheme. Hence the combination of LBM and SPM can be considered as an efficient and promising method for simulating flow in porous media.

Electromagnetic binding and radiation force reversal on a pair of electrically conducting cylinders of arbitrary geometrical cross-section with smooth and corrugated surfaces

The electromagnetic (EM) radiation force-per-length exerted on a pair of electrically-conducting cylindrical particles of circular and non-circular cross-sections is examined using a formal semi-analytical method based on boundary matching in cylindrical coordinates. Initially, the scattering coefficients of the particle pair are determined by imposing suitable boundary conditions leading linear systems of equations computed via matrix inversion and numerical integration procedures. Standard cylindrical (Bessel and Hankel) wave functions are used and closed-form expressions for the dimensionless longitudinal and transverse radiation force functions are evaluated assuming either magnetic (TE) or electric (TM) plane wave incidences. Particle pairs with smooth and corrugated surfaces are considered and numerical computations are performed with emphasis on the distance separating their centers of mass, the angle of incidence of the incident illuminating field and the surface roughness. Adequate convergence plots confirm the validity of the method to evaluate the radiation force functions, and the model is adaptable to any frequency range (i.e. Rayleigh, Mie or geometrical optics regimes). The results can find potential applications in optical tweezers and other related applications in fluid dynamics. In addition, the acoustical analogue is discussed.

Effect of contact location on the crushing strength of aggregates

This work deals with the effect of the contact location distribution on the crushing of granular materials. At first, a simple drop weight experiment was designed in order to study the effect of the location of three contact edges on the fracture pattern and the strength of a model cylindrical particle. The sample was placed on two bottom contact edges symmetrically distributed with reference to the vertical symmetry plane of the particle and subjected to an impact at the top. Angle α between the plane connecting a bottom contact edge to the centerline of the cylinder and a vertical plane was varied. The energy required to fracture the particle was shown to be an increasing function of angle α. Peculiar crack patterns were also observed. Then, we present a discrete model of grain fracture based on the work of Neveu et al. (2016) and employ it for a numerical analysis of the problem. The cylindrical particle is discretized by means of a space filling Voronoï tessellation, and submitted to a compression test for different values of angle α. In agreement with experiments, simulations predict a strong effect of the contact orientation on the strength of the particle as well as similar fracture patterns. The effect of the number of contacts is also explored and the importance of a potential pre-load is emphasized. We show that the fracture pattern: (i) is diametrical in case of diametrically opposed edges, (ii) has an inverted Y-shape in the case of three or four edges. Interestingly, in the latter case, if one of the lateral edges is slightly shifted, the fracture initiates and even propagates diametrically. Furthermore, the particle strength increases with the number of contacts.

Effective magnetic susceptibility of suspensions of ferromagnetic particles

The effective susceptibility χeff of suspensions of ferromagnetic particles in a liquid was measured using inductance measurements. These measurements were used to test a model that predicts how χeff varies due to demagnetization, as a function of sample aspect ratio, particle packing fraction, and particle aspect ratio [R. Skomski, G. C. Hadjipanayis, and D. J. Sellmyer, IEEE Trans. Magn. 43, 2956–2958 (2007)]. For spherical particles or cylindrical particles forcibly aligned with an external magnetic field, the model can be fitted to the measured data with agreement within 13%. This model predicts suspensions of aligned, large-aspect-ratio particles should have the largest χeff, approaching the particle material susceptibility in the limit of large particle aspect ratio. However, χeff was found to be no larger than about 4 for cylindrical iron particles of various aspect ratios, close to the value obtained for spheres. This results from the random alignment of non-spherical particles relative to the magnetic field naturally found in suspensions, which increases the demagnetization effect and limits χeff. The contribution of random particle alignments to the demagnetization effect and χeff remains to be accounted for in models.

Thermal characteristics of single wood particle pyrolysis using particle image velocimetry

This study examines the pyrolysis of a single cylindrical wood particle using Particle Image Velocimetry (PIV). The pyrolysis was carried out in the ATR 01/600 pyrolysis reactor designed for this purpose. The experimental setup presented in this study is capable of effectively characterizing the intensity of pyrolysis based on velocity distribution in the vicinity of wood particles. The results of the gas velocity distribution indicate the formation of a gas cushion caused by the evaporation of moisture and devolatilization. Higher heating rates increase the intensity of degassing and the thickness of the gas cushion around the particle and may temporarily slow down the intensity of convective heat transfer to the interior of the particle.

Highly selective transmission and absorption from metasurfaces of periodically corrugated cylindrical particles

Gratings of infinite wires make, perhaps, the simplest class of metasurfaces, which, however, are utilized for a variety of different objectives in wave manipulation. Importantly, due to their analytical solvability, they can be fully optimized in a fast and direct way. In this study, a lattice of periodically corrugated cylindrical particles under oblique plane-wave excitation is considered and treated rigorously. Several cases of particle radii, distances between two consecutive cylinders, and angles of illumination are examined; as a result, very high selectivity of the metasurface response in terms of line-of-sight transmission and absorption is reported. That abrupt change in the device output becomes even more dramatic in the parametric vicinity of the emergence of new refractive orders, which makes the proposed metasurface exceptionally fitting for switching, filtering, and sensing applications.

Evolutions of packing properties of perfect cylinders under densification and crystallization.

Cylindrical particles are ubiquitous in nature and industry, and a cylinder is a representative shape of rod-like particles. However, the disordered packing results of cylinders in previous studies are quite inconsistent with each other. In this work, we obtain the MRJ (maximally random jammed) packings and the MDRPs (maximally dense random packings) of perfect cylinders with the aspect ratio (height/diameter) 0.2 ≤ w ≤ 6.0 using the ASC (adaptive shrinking cell) algorithm and the IMC (inverse Monte Carlo) method, respectively. The optimal aspect ratio corresponding to the maximal packing density is w = 0.9 in the MRJ state, while the value is w = 1.2 in the MDRP state. Then we investigate the evolutions of packing properties of perfect cylinders under densification and crystallization. We compare the different final packing states generated via the two methods with different compression rates and order constraints. In the densification procedure, we generate jammed and random packings of cylinders with various compression rates via the ASC and IMC method, respectively. When decreasing the compression rate, we find that the packing density increases but the optimal w remains the same in both methods. In the crystallization procedure, the order constraint in the IMC method is gradually released which means the degree of order in the packings is allowed to increase, and we find that the optimal w shifts from 1.2 to 0.9 while the packing density increases as well. Meanwhile, the random packings evolve into the jammed packings in the crystallization procedure which reflects the competition mechanism between the randomness and jamming. These results also indicate that the optimal w is solely related to the degree of order in the cylinder packings but not determined by the protocol or packing density. Furthermore, a uniform shape elongation effect on the random-packing densities of various shaped particles is found via a new proposed definition of the scaled aspect ratio. Finally, a rough linear relationship between the mean and standard deviation of the reduced Voronoi cell volumes is obtained only for the random packings. Our findings should lead to a better understanding toward the jammed and random packings and are helpful in guiding the granular material design.

Monte Carlo simulation of cylinders with short-range attractions.

Cylindrical or rod-like particles are promising materials for the applications of fillers in nanocomposite materials and additives to control rheological properties of colloidal suspensions. Recent advances in particle synthesis allows for cylinders to be manufactured with short-ranged attractions to study the gelation as a function of packing fraction, aspect ratio and attraction strength. In order to aid in the analysis of small-angle scattering experiments of rod-like particles, computer simulation methods were used to model these particles with specialized Monte Carlo algorithms and tabular superquadric potentials. The attractive interaction between neighboring rods increases with the amount of locally-accessible surface area, thus leading to patchy-like interactions. We characterize the clustering and percolation of cylinders as the attractive interaction increases from the homogenous fluid at relatively low attraction strength, for a variety of aspect ratios and packing fractions. Comparisons with the experimental scattering results are also presented, which are in agreement.

The Effect of Phase Separation on Diffusion Induced Stresses in Spherical and Cylindrical Electrode Particles

The Effect of Phase Separation on Diffusion Induced Stresses in Spherical and Cylindrical Electrode Particles

Effect of non-stoichiometry in lead hexaferrites on magnetic and dielectric properties

The effect of iron deficiency on the structural, electrical and magnetic properties of the nano PbFe12-xO19-δ (where x = 0.0, 0.25, 0.50, 0.75 and 1.0) hexaferrites prepared by sol-gel auto combustion and further processed by microwaves is presented. The structure studied using transmission electron microscope (TEM) showed hexagonal cylindrical particles with an average size of ∼20 nm. Selected area electron diffraction (SAED) reflected highly crystalline nature of these nanoparticles. From the dielectric characterizations ac-conductivity, dielectric constant and loss tangent are analysed for pure and modified PbFe12-xO19-δ hexaferrites. The magnetic analysis revealed the formation of single-domain structure. Saturation magnetization (MS) decreases from 63.2 (x = 0) to 38.2 (x = 1.0) emu/g with increasing the Fe ions deficiency. Room temperature Mössbauer spectra show five sextets for all compositions confirmed the single phase formation. The relative area of 12k (↑) site decreases and 4f2 (↓) increases drastically with increasing the Fe ions deficiency in Pb-hexaferrites.

Acoustic radiation force of attraction, cancellation and repulsion on a circular cylinder near a rigid corner space

• The acoustic radiation force on a cylindrical particle near a corner space is determined. • Plane progressive waves with an arbitrary incidence angle are considered. • Depending on the distances, incidence angle and particle size, particle neutrality is yielded. • Attraction or repulsion forces to the corner space can also arise. • Potential applications are in acoustofluidics applications and related areas of research. The purpose of this study is to derive exact partial wave series expansions for the longitudinal and transverse radiation force components, for a circular cylinder in the proximity of a rigid corner space, and illuminated by incident plane waves with arbitrary orientation in the polar plane. Based on the multipole expansion method in cylindrical coordinates , the method of images as well as the translational addition theorem , an effective incident field (resulting from the primary waves as well as the multiple scattered fields from the image sources) is determined first, and used subsequently with the scattered field to derive the mathematical expressions for the radiation force components, stemming from the integration of the radiation stress in a non-viscous fluid. Numerical computations illustrate the analysis for rigid and soft cylinders with particular emphasis on the distances from the particle edges to the neighbouring walls, the size of the cylinder and the angle of incidence. Depending on the choice of these parameters, the radiation force components can vanish, rendering complete “invisibility”; i.e., the cylinder becomes unresponsive to the transfer of linear momentum carried by the incident effective field. Moreover, the radiation force components alternate between positive and negative values, suggesting a force of repulsion or attraction. The results find potential applications in acoustofluidics design and optimization as they shed light on the anechoic radiation force effect on a particle nearby a rigid corner. Other applications in noise and vibration control could also benefit from the results of the present investigation along with further related topics.

Synthesis and catalytic activity of chrysotile-type magnesium silicate nanotubes using various silicate sources

Abstract Chrysotile-type Mg3Si2O5·(OH)4 nanotubes (MgSi-NTs) were obtained (by a hydrothermal method) using different SiO2 sources. Sources of silica, as raw material, were varied from sodium silicate (typical preparation) to colloidal silica of 12–22 nm colloid size. Around 13 g of MgSi-NTs were prepared by using 7.8 L Teflon-lined autoclave at 240 °C. In all synthesis attempts, XRD was used to identify chrysotile crystal phases, which were later confirmed by TEM, showing bundles of hollow cylindrical particles of MgSi-nanotubes from 60 to 218 nm length and internal diameters from 5 to 8 nm. Specific surface areas obtained by nitrogen adsorption of MgSi-NTs samples (annealed at 600 °C) were between 105 and 202 m2/g with average pore diameter from 7 to 32 nm, depending on silica precursor. Thermal stability of MgSi-NTs was examined by TGA-DTA, XRD and TEM. From TEM images, it was clear that nanotubes from colloidal silicas can hold up below 600 °C. Sodium silicate obtained nanotubes were less thermally stable (below 500 °C), though. The use of colloidal silica, instead of sodium silicate, upgraded specific surface area and pore volume values of resulting MgSi-NTs. Number of basic sites and properties were measured by CO2-TPD ranging between 66 and 89 μmol CO2/g cat, and their catalytic activity was assessed on aldol condensation of acetone reaction at 300–350 °C, where the main products obtained were mesityl oxide and isophorone, which are valuable products for fine-chemistry industry.

Quasiperiodic granular chains and Hofstadter butterflies.

We study quasiperiodicity-induced localization of waves in strongly precompressed granular chains. We propose three different set-ups, inspired by the Aubry-André (AA) model, of quasiperiodic chains; and we use these models to compare the effects of on-site and off-site quasiperiodicity in nonlinear lattices. When there is purely on-site quasiperiodicity, which we implement in two different ways, we show for a chain of spherical particles that there is a localization transition (as in the original AA model). However, we observe no localization transition in a chain of cylindrical particles in which we incorporate quasiperiodicity in the distribution of contact angles between adjacent cylinders by making the angle periodicity incommensurate with that of the chain. For each of our three models, we compute the Hofstadter spectrum and the associated Minkowski-Bouligand fractal dimension, and we demonstrate that the fractal dimension decreases as one approaches the localization transition (when it exists). We also show, using the chain of cylinders as an example, how to recover the Hofstadter spectrum from the system dynamics. Finally, in a suite of numerical computations, we demonstrate localization and also that there exist regimes of ballistic, superdiffusive, diffusive and subdiffusive transport. Our models provide a flexible set of systems to study quasiperiodicity-induced analogues of Anderson phenomena in granular chains that one can tune controllably from weakly to strongly nonlinear regimes.This article is part of the theme issue 'Nonlinear energy transfer in dynamical and acoustical systems'.