Lattice Boltzmann simulation of flow past a non-spherical particle

Lattice Boltzmann method was used to predict the fluid-particle interaction for arbitrary shaped particles. In order to validate the reliability of the present approach, simulation of flow past a single stationary spherical, cylindrical or cubic particle is conducted in a wide range of Reynolds number (0.1 < Re_p < 3000). The results indicate that the drag coefficient is closely related to the particle shape, especially at high Reynolds numbers. The voxel resolution of spherical particle plays a key role in accurately predicting the drag coefficient at high Reynolds numbers. For non-spherical particles, the drag coefficient is more influenced by the particle morphology at moderate or high Reynolds numbers than at low ones. The inclination angle has an important impact on the pressure drag force due to the change of projected area. The simulated drag coefficient agrees well with the experimental data or empirical correlation for both spherical and non-spherical particles.     

Numerical study on deposition of non-spherical shaped particles in cascade impactor

This study investigated the deposition of non-spherical particles in a cascade impactor using numerical simulations based on computational fluid dynamics and a discrete phase model (CFD-DPM). An optimum drag force model of non-spherical particles was used to calculate the dynamic behavior of the needle-shaped particles. The trajectory of these particles in an elbow pipe was computed and measured using a high-speed video camera. The computed trajectory agreed well with the experimental trajectory, and it was confirmed that the drag force model of non-spherical particles correctly expressed the drag force in the CFD-DPM numerical simulation. Next, the motion of the needle-shaped particles in a cascade impactor was numerically simulated and compared with that in the experimental results. The simulated classification efficiency agreed well with the experimental results. Additionally, the relationship between the aspect ratio of the needle-shaped particles and their behavior in the cascade impactor was numerically analyzed. The cut-off diameter decreased with the aspect ratio at a 50% classification efficiency in the cascade impactor. This was because the drag force of the particle was assumed to increase with the aspect ratio, and longer particles fell at a lower stage in the cascade impactor.     

Effect of surface slip on Stokes flow past a spherical particle in infinite fluid and near a plane wall

The motion of a spherical particle in infinite linear flow and near a plane wall, subject to the slip boundary condition on both the particle surface and the wall, is studied in the limit of zero Reynolds number. In the case of infinite flow, an exact solution is derived using the singularity representation, and analytical expressions for the force, torque, and stresslet are derived in terms of slip coefficients generalizing the Stokes–Basset–Einstein law. The slip velocity reduces the drag force, torque, and the effective viscosity of a dilute suspension. In the case of wall-bounded flow, advantage is taken of the axial symmetry of the boundaries of the flow with respect to the axis that is normal to the wall and passes through the particle center to formulate the problem in terms of a system of one-dimensional integral equations for the first sine and cosine Fourier coefficients of the unknown traction and velocity along the boundary contour in a meridional plane. Numerical solutions furnish accurate predictions for (a) the force and torque exerted on a particle translating parallel to the wall in a quiescent fluid, (b) the force and torque exerted on a particle rotating about an axis that is parallel to the wall in a quiescent fluid, and (c) the translational and angular velocities of a freely suspended particle in simple shear flow parallel to the wall. For certain combinations of the wall and particle slip coefficients, a particle moving under the influence of a tangential force translates parallel to the wall without rotation, and a particle moving under the influence of a tangential torque rotates about an axis that is parallel to the wall without translation. For a particle convected in simple shear flow, minimum translational velocity is observed for no-slip surfaces. However, allowing for slip may either increase or decrease the particle angular velocity, and the dependence on the wall and particle slip coefficients is not necessarily monotonic.     

A combined physical and DEM modelling approach to investigate particle shape effects on load movement in tumbling mills

The discrete element method (DEM) which is used to simulate granular flows often assumes spherical shape for particles. This assumption is legitimized by the added complexity of non-spherical shape representation, contact detection and computational cost. In this work, the difference between the dynamics of non-spherical and spherical particles was studied in detail by a combined physical and DEM modeling approach. An in-house developed DEM software called KMPC_DEM©, which was coded to handle non-spherical particles, was used to simulate the behavior of particles. To calibrate the model parameters, a model tumbling mill (100 cm diameter and 10.8 cm length) with one transparent end was used which made accurate photography possible. The tests were performed at filling of 20% and mill speed of 85% of critical speed with steel balls and wood cubes. In the simulation, each cubical particle was represented with clusters of spheres (with identical size) by particle packing algorithm for contact detection and contact-force calculation. Comparison of the simulation and experimental results showed that the difference between the measured and predicted impact toe, shoulder angle and bulk toe angle were 3, 4 and 5°, respectively. The significant change in the charge movement and structure on account of non-spherical particles was reflected in the amount of in-flight charge, and positions of shoulder, impact toe and bulk toe. It found that there was a 17% difference in the amount of in-flight of charge between cubical and spherical particles. The marked difference was attributed to higher interlocking of non-spherical particles in comparison to spherical balls. The results showed that cubical particles participated 5% more in the high energy impact action compared to that of the spherical particles. The simulation computation time increased by 35 times when the shape of particles changed from spherical to cubical.     

Investigation of spherical and non-spherical binary particles flow characteristics in a discharge hopper

The particulate flow characteristics of granular particles including mung beans, wooden spheres, wooden cylinders, wooden cubic, plastic spheres, plastic cylinders, and their binary mixtures in a flat bottom hopper were studied experimentally using high-speed high-resolution camera recordings. An image processing method based on the color threshold was developed to calculate the area ratio for binary mixtures. The mass discharge rates, the residue inclination angles, and the changes in edge height and center height with time were also investigated. In addition, the effects of different initial packing patterns on the particulate flow, mixing and segregation behaviors were analyzed and compared. It is interesting to find that the shape of particles and the initial binary particle packing patterns have significant effects on the discharging characteristics. The results of this study provide helpful guidance for industrial applications and provide experiment data for computational model validation.     

Effects of main particle diameter on improving particle flowability for compressed packing fraction in a smaller particle admixing system

Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the mechanisms by which this technique improves flowability are not yet fully understood. In this study, we examined compressed packing in a particle bed, which is affected by particle flowability. To estimate the mechanism of improvement, we investigated the effects of the main particle diameter on the improvement of compressed packing fractions experimentally.The main particles were 397 and 1460 nm in diameter and the admixed particles were 8, 21, 62, and 104 nm in diameter. The main and admixed particles were mixed in various mass ratios, and the compressed packing fractions of the mixtures were measured. SEM images were used to analyze the coverage diameter and the surface coverage ratio of the admixed particles on the main particles. The main particle packing fraction was improved as the diameter ratio (=main particles/admixed particles) increased. This was explained by a linked rigid-3-bodies model with leverage. Furthermore, the actual surface coverage ratio at which the most improved packing fraction was obtained decreased with increasing main particle diameter. This was explained by the difference in the curvature of the main particle surface.     

Attraction force, frictional torque, and heating of a spherical particle rotating in the evanescent electromagnetic field of a heated surface

For the first time, we have calculated the attraction force, frictional torque, and heating rate that are caused by fluctuation-electromagnetic interaction of a small spherical particle uniformly rotating at a constant angular velocity near a heated surface. Closed analytical formulas are obtained for these quantities. It is shown that the stopping time of a particle rotating in the near field of the surface is much less than the stopping time under rotation in vacuum space.     

Experimental and numerical modeling of particle levitation and movement behavior on traveling-wave electric curtain for particle removal

Traveling-wave electric curtain (EC) has been developed for potential application in particle removal/shield on solar panels and other surfaces. Levitation and transport of a particle in a traveling-wave electric field were simulated. Results show that levitation directions/angles and levitation trajectories differ because of the difference in starting positions and starting times. The particles in the two positive acceleration regions are levitated in opposite directions, and the particles distributed on the dielectric surface are levitated and transported successively rather than simultaneously. Movement trajectories are complex and affected by various factors. In the current paper, movement trajectories are modeled to analyze which motion modes are advantageous or disadvantageous to particle removal. This process is beneficial to elucidate the mechanism of particle removal and provide a guidance for movement control by designing appropriate operating parameters.     

Drag force acting on a neuromast in the fish lateral line trunk canal. II. Analytical modelling of parameter dependencies

In Part I of this two-part study, the coupled flows external and internal to the fish lateral line trunk canal were consecutively calculated by solving the Navier–Stokes (N–S) equations numerically in each domain. With the external flow known, the solution for the internal flow was obtained using a parallelepiped to simulate the neuromast cupula present between a pair of consecutive pores, allowing the calculation of the drag force acting on the neuromast cupula. While physically rigorous and accurate, the numerical approach is tedious and inefficient since it does not readily reveal the parameter dependencies of the drag force. In Part II of this work we present an analytically based physical–mathematical model for rapidly calculating the drag force acting on a neuromast cupula. The cupula is well approximated as an immobile sphere located inside a tube-shaped canal segment of circular cross section containing a constant property fluid in a steady-periodic oscillating state of motion. The analytical expression derived for the dimensionless drag force is of the form |FN|/(|PL−PR|π(D/2)2)=f(d/D,Lt/D,ωD*), where |F_N| is the amplitude of the drag force; |P_L−P_R| is the amplitude of the pressure difference driving the flow in the interpore tube segment; d/D is the ratio of sphere diameter to tube diameter; L_t/D is the ratio of interpore tube segment length to tube diameter; and ωD*=ω(D/2)2/ν is the oscillating flow kinetic Reynolds number (a dimensionless frequency). Present results show that the dimensionless drag force amplitude increases with decreasing L_t/D and maximizes in the range 0.65≤d/D≤0.85, depending on the values of L_t/D and ωD*. It is also found that in the biologically relevant range of dimensionless frequencies 1≤ωD*≤20 and segment lengths 4≤L_t/D≤16, the sphere tube (neuromast–canal) system acts as a low-pass filter for values d/D≤0.75, approximately. For larger values of d/D the system is equally sensitive to all frequencies, but the drag force is significantly decreased. Comparisons with N–S calculations of the drag force show good agreement with the analytical model results. By revealing the parameter dependencies of the drag force, the model serves to guide biological understanding and the optimized design of corresponding bioinspired artificial sensors.     

利用粒子群优化算法实现阻尼比和频率的精确识别

摘要：本文提出了一种利用粒子群优化算法辨识阻尼比和频率的方法。该方法将系统频率、阻尼比、幅值和相位的辨识问题转化为非线性优化问题,引入粒子群优化算法寻找全局最优解。基于粒子群优化的阻尼比和频率辨识方法不需要测量激励信号,原理简单,实现容易。仿真和实验结果表明：基于粒子群优化算法的阻尼比和频率辨识方法不受邻近模态耦合的影响。在无噪声条件下具有较高的辨识精度,随着信噪比的逐步降低,辨识精度开始逐步下降。用低通滤波器滤除高阶模态后,得到的脉冲响应信号对频率、阻尼比、幅值的辨识精度影响很小,对相位的辨识精度影响很大。

     

Effect of constituent particle polydispersion on VSSA-based equivalent particle diameter: Theoretical rationale and application to a set of eight powders with constituent particle median diameters ranging from 9 to 130 nm

Volume Specific Surface-Area (VSSA) has been identified as a relevant and alternative method to electron microscopy (EM) to determine whether a material is or not a nanomaterial. VSSA is an integral measurement method that provides an indirect representation of particle size. When this conversion into particle diameter is carried out, constituent particles are supposed to be monodisperse, which can be considered far from reality, materials being composed of polydisperse constituent particles. The way particle polydispersion affects the VSSA of a material, and thus the equivalent particle diameter deduced, is investigated in this paper. In particular, the specific case of normally-distributed, spherical constituent particles, is considered. A theoretical study has led to the introduction of a correction polydispersion-based factor. From experimental VSSA data obtained for eight powders covering a range of constituent particle median diameters from 9 to 130 nm, the VSSA-based constituent particle median diameters were compared to the median constituent particle size obtained from electron microscopy analysis, considered as the reference method. Integrating constituent particle polydispersion through the use of the correction factor improves the accuracy of particle size stemming from the VSSA approach, the relative discrepancies being within ±20% from the reference diameter.     

Effects of discharging vibration conditions and coating structures on improving discharge particle flowability in a smaller particle admixing system

Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the effects of coating structures on the improvement of flowability are not yet fully understood. In this study, we focused on vibrating discharge particle flowability and investigated the effect of discharging vibration conditions and coating structures on improving the flowability. Main and admixed particles of 60.8 μm and 8 nm in diameter, respectively, were mixed in various mass ratios, and the discharge particle flow rates of the mixed particles were measured. Scanning electron microscopy and scanning probe microscopy images were used to analyze the coverage diameter, surface coverage ratio, and coverage height of the admixed particles on the main particle surfaces. As a result, the admixing mass ratio that gave maximum flowability was found to depend on the maximum value of the vibration acceleration. This could be explained by the relationship between the coating structures of admixed particles and the coated average surface distances due to the vibration acceleration.     

HEC-cysteamine particles: influence of particle size,zeta potential,morphology and sulfhydryl groups on permeation enhancing properties

Within this study, the influence of particle size and zeta potential of hydroxyethyl cellulose–cysteamine particles on permeation enhancing properties was investigated. Particles were prepared by four different methods namely ionic gelation, spray drying, air jet milling and grinding. Particles prepared by grinding were additionally air jet milled. All particles were characterized in terms of particle size and zeta potential. The transport of fluorescein isothiocyanate-dextran 4 (FD4) across Caco-2 cell monolayers in the presence of these particles and the decrease in transepithelial electrical resistance (TEER) was evaluated. The cytotoxic effect of the particles was investigated using resazurin assay. Nanoparticles displaying a zeta potential of 3.3?±?1.3 mV showed the highest enhancement of FD4 transport among all particles with a 5.83-fold improvement compared to buffer only. Due to the larger particle size, particles generated by grinding exhibited a lower capability in opening of tight junctions compared to smaller particles generated by air jet milling. In addition, the results of the transport studies were supported by the decrease in the TEER. All particle formulations tested were comparatively non-cytotoxic. Accordingly, the zeta potential and particle size showed a significant impact on the opening of tight junctions and hence could play an important role in the design of hydroxyethyl cellulose (HEC)-cysteamine-based nano- and micro-particles as drug delivery systems.     

CFD-DEM study on the mixing characteristics of binary particle systems in a fluidized bed of refuse-derived fuel

The fluidization of quartz in the fluidized bed has great influence on the combustion and gasification of refuse-derived fuel (RDF). The combined computational fluid dynamics (CFD) and discrete element method (DEM) approach was used to explore the gas-solid hydrodynamics and mixing characteristics in a three-dimensional fluidized bed. All numerical analyses were performed referring to the experiments (Goldschmidt, Beetstra, and Kuipers 2004 Goldschmidt, M. J. V., R. Beetstra, and J. A. M. Kuipers. 2004. Hydrodynamic modelling of dense gas-fluidised beds: Comparison and validation of 3D discrete particle and continuum models. Powder Technology 142 (1):23–47. doi:10.1016/j.powtec.2004.02.020[Crossref], [Web of Science ®] , [Google Scholar]). The simulation results indicated that the quartz volume fraction agrees well with the experimental data. Furthermore, the cylinder-shaped RDF particles can mix well with the quartz particles as they were added from upside. For binary systems, it is necessary to investigate solid flow characteristics as well as pressure drops and examine the influence of superficial gas velocity on the solid mixing. Two main parameters are discussed: mixing degree and the time required to reach the steady state. It is also found that inlet gas velocity and particle properties (particle density ratio, shape and size) are significant factors on particle mixing in a fluidized bed.     

An accurate and stable multiphase moving particle semi‐implicit method based on a corrective matrix for all particle interaction models

The Lagrangian moving particle semi‐implicit (MPS) method has potential to simulate free‐surface and multiphase flows. However, the chaotic distribution of particles can decrease accuracy and reliability in the conventional MPS method. In this study, a new Laplacian model is proposed by removing the errors associated with first‐order partial derivatives based on a corrected matrix. Therefore, a corrective matrix is applied to all the MPS discretization models to enhance computational accuracy. Then, the developed corrected models are coupled into our previous multiphase MPS methods. Separate stabilizing strategies are developed for internal and free‐surface particles. Specifically, particle shifting is applied to internal particles. Meanwhile, a conservative pressure gradient model and a modified optimized particle shifting scheme are applied to free‐surface particles to produce the required adjustments in surface normal and tangent directions, respectively. The simulations of a multifluid pressure oscillation flow and a bubble rising flow demonstrate the accuracy improvements of the corrective matrix. The elliptical drop deformation demonstrates the stability/accuracy improvement of the present stabilizing strategies at free surface. Finally, a turbulent multiphase flow with complicated interface fragmentation and coalescence is simulated to demonstrate the capability of the developed method.     

Pre-adolescent children exhibit lower aerosol particle volume emissions than adults for breathing,speaking, singing and shouting

Speaking and singing are activities linked to increased aerosol particle emissions from the respiratory system, dependent on the utilized vocal intensity. As a result, these activities have experienced considerable restrictions in enclosed spaces since the onset of the COVID-19 pandemic due to the risk of infection from the SARS-CoV-2 virus, transmitted by virus-carrying aerosols. These constraints have affected public education and extracurricular activities for children as well, from in-person music instruction to children’s choirs. However, existing risk assessments for children have been based on emission measurements of adults. To address this, we measured the particle emission rates of 15 pre-adolescent children, all eight to ten years old, with a laser particle counter for the test conditions: breathing at rest, speaking, singing and shouting. Compared with values taken from 15 adults, emission rates for breathing, speaking and singing were significantly lower for children. Particle emission rates were reduced by a factor of 4.3 across all conditions, whereas emitted particle volume rates were reduced by a factor of 4.8. These data can supplement SARS-CoV-2 risk management scenarios for various school and extracurricular settings.     

高分子量PAN的粒径分布与均匀度关系的考察

对高性能碳纤维原丝性能有重要影响的聚合物粒径均匀度问题目前尚未有人研究过。本研究率先采用沉淀聚合合成高分子量PAN,根据其微观形貌,应用第四统计力学群子统计参数理论研究了聚合物的粒径分布与粒径均匀度的关系,表明粒径均匀度与混合溶剂无关,而与混合溶剂的配比有关,DMSO含量越少,粒径分布越均匀。     

Experimental study on the discharge flow rate of binary mixture in a two-dimensional silo

In this work, the discharging process of the binary mixture composed of sphere and sphere-paired particles in a two-dimensional silo was studied. High-speed camera and self-developed particle tracking velocimetry (PTV) program were used to capture the flow behaviors of all particles. The key parameters of mixed flow, including coordination number, horizontal displacement and mechanical energy loss in the discharge process, were highlighted. It was found that the increase of sphere-paired particles can decrease the average coordination number of particles during the discharging process. The analysis about the loss of mechanical energy and the horizontal displacement of particles indicated that sphere-paired particles preferentially squeezed out sphere particles from fast flow field above the outlet. Moreover, an empirical formula was proposed to assess the influence of the proportion of sphere-paired particles on the discharge flow rate. Sphere-paired particles tended to hinder the discharging process, which was caused by the rotation around their centroids and the angular deflection close to angle of the hopper.     

Dissipation of the fluctuational electromagnetic field energy, tangential force, and heating rate of a neutral particle moving near a flat surface

A relationship between the dissipation of the fluctuational electromagnetic field energy, tangential (decelerating) force, and heating rate of a neutral particle moving parallel to a plane polarizable surface is considered for the first time in a nonrelativistic approximation. The formulas obtained take into account dielectric properties of the particle and surface.     

In situ studies of misch-metal particle behavior on a molten stainless steel surface

The use of misch-metal is widely spread among the stainless steel producers. Casting problems like clogging are common when using these additions. Information about Ce–La–Al–O particles formed due to the addition of misch-metal in the ladle is scarce in the open literature. The aim of this study is to increase the knowledge of the particle behavior and the particle characteristics in two stainless steels resulting from the addition of misch-metal. The in situ particle behavior has been studied using a Confocal Laser Scanning Microscope.