Mechanisms Of Particle Dispersion Research Articles

Light-transmitting AlON carrier with enhanced photocatalytic degradation performance

A skeleton structure AlON (aluminum oxynitride) carrier with light transmission performance was prepared by carbothermal reduction and nitridation (CRN). The AlON carrier can disperse nano active components and enhance its photocatalytic performance. The microstructure of the TiO2/AlON composite photocatalyst shows that the dispersion of the agglomerated TiO2 is achieved by the physical adsorption mechanism, the embedding mechanism and the single particle dispersion mechanism. The morphology of the BiVO4/AlON and g-C3N4/AlON composite photocatalysts further proves the universality of the AlON carrier in the dispersion of nano photocatalyst. The photocatalytic performance of the nano active component was enhanced by combining with AlON carrier. After 240 min of visible light irradiation, the degradation rate of MB increased by 7.4% (BiVO4/AlON) and 8.1% (g-C3N4/AlON), respectively. High light transmittance was the main reason for AlON carrier to improve the photocatalytic performance of loaded active components. In addition, AlON carrier type composite photocatalyst can be reused for many times because it has physicochemical stability and can be recovered easily.

Preparation and characterization of ZnFe1.2Cr0.8O4 water-based ceramic inks obtained using a polymeric dispersant

Reddish-brown water-based ceramic inks composed of ZnFe1.2Cr0.8O4 pigment, a polymeric dispersant AD01, and some additives, were successfully obtained by grinding method. The effect of dispersant on ceramic inks, especially particle size and distribution were investigated. The grinding and dispersion mechanism of particles in the grinding processing has been discussed. The stability of particles in ceramic inks was also evaluated. Moreover, the inkjet printing performances of the water-based ceramic inks were predicted by using the dimensionless parameters Reynolds number (Re), Weber number (We), and Ohnesorge number (Oh). The results show that the water-based ceramic inks with appropriate viscosity (12.05–23.05 mPa·s), surface tension (27.7–31.7 mN/m) and density (1.331–1.348 g/cm3) can satisfy the inkjet printing requirements, and show excellent coloring ability on ceramic glaze, indicating that the water-based ceramic inks prepared have a promising application prospect.

Ultrasound-assisted dispersion of TiB2 nanoparticles in 7075 matrix hybrid composites

Refinement and dispersion of rigid ceramic particles enhance the mechanical properties of particulate reinforced aluminum matrix composites (PRAMCs). However, nanoparticles are intrinsically clustered or agglomerated together in melts and thereby reduce their strengthening efficacy. Ultrasound cavitation and acoustic streaming can effectively improve the distribution of nanoparticles in melts. In this work, we use synchrotron radiation X-ray computed tomography (SR-CT) to unveil the particle dispersion mechanism by ultrasound vibration treatment (UVT) from three-dimensional perspective. The SR-CT results indicated that the mesoscale agglomerates in a high-strength 7075 aluminum alloys can be eliminated completely upon UVT. Two types of TiB2 particles have been identified, termed as micro-size TiB2 particles (MTPs) and nano-size TiB2 particles (NTPs), which were observed to be aggregated along the grain boundaries and dispersed uniformly within the α-Al grains, respectively. Tensile tests reveal significant strengthening of the composites in the as-cast state, suggesting effective Orowan strengthening. This strength enhancement is attributed to the dispersed NTPs that have been retained after solidification. It is also inspiring to see the concurrent increase in the ductility of the composites after UVT, thanks to the improvement in particle distribution.

Large eddy simulation of aerosol particle dispersion mechanism in aircraft exhaust plume

Aerosol Infrared Stealth Technology is a novel method to suppress the infrared by releasing aerosol particles around the hot exhaust plume. However, the Infrared Radiation (IR) suppression rate is much lower in flight tests, which is caused by the unclear particle dispersion mechanism in high-speed non-isothermal shear flow. Hence, the large eddy simulation (LES) and particle discrete phase model (DPM) are coupled to solve the turbulent shear flow and the aerosol particle motion. The effects of aircraft flight speed on the turbulent flow characteristics and particle motion behaviors are systematically studied. It is found that the Mach rings appear in flight conditions, and they are getting blurry when increasing the flight speed. Both γ-like vortex and horseshoe-like vortex are observed when Ma < 1, and the horse-like could disappear when Ma > 1. The aerosol particle distribution is closely related to the turbulent gas vortices. The particle lateral dispersion is obviously restricted with the rising flight speed. Besides, the drag force plays a dominant role, the Saffman force and the thermophoretic force are of the same order of magnitude, all of these three forces are much greater than the gravity.

Effect of liquid–air interface on particle cloud dynamics in viscous liquids

Three-dimensional numerical investigations have been performed to study the effect of liquid–air interface on particle cloud evolution in the stagnant pool of viscous liquid. Computations have been carried out using open-source computational fluid dynamics package open-source field operation and manipulation under different operating conditions. A hybrid multifluid–volume-of-fluid-based solver is used to identify the influence of liquid–air interface on particle cloud dynamics. Mainly, two different operating conditions have been considered in the present study, viz., falling particle cloud within the liquid and falling from the liquid–air interface. The effect of particle Reynolds number (Re) on cloud evolution has also been considered in the present study. The effect of the liquid–air interface on particle cloud dynamics has been qualitatively explained with the help of particle volume fraction iso-surface, liquid velocity vectors, and iso-Q-surface, and quantitatively explained with the help of average particle cloud velocity, penetration depth, plume half-width, and particle cloud mass. Proper orthogonal decomposition-based analysis has been used to explain the vortex structures generated in the viscous fluid for different cases. Releasing particle cloud from liquid–air interface decreases radial spreading as compared to the case of particle release within the liquid. Particle cloud evolution pattern is found to depend on particle Reynolds number only for the case with the liquid–air interface. The liquid–air interface's downward movement enhances and upward movement suppresses the spreading of the particle cloud, which subsequently alters the particle dispersion mechanisms in the later stages.

An algorithm for tracking drifters dispersion induced by wave turbulence using optical cameras

The automatic detection of passive tracers on a moving wavy surface has numerous applications in mathematics and engineering. In oceanography, among many examples, down-looking conventional optical cameras can be employed in wave tanks to investigate the mechanisms of particle dispersion induced by wave turbulence. In this context, we present a computational system to automatically track down the trajectories of several identical passive floaters under the influence of mechanically generated water waves with distinct spectral features. Such functionality is not yet publicly available and a free/open source code within the Python programming environment is described and evaluated. The code is robust and fast, able to automatically identify drifters at 30 fps during approximately 40 seconds, while they remained in the camera’s field of view. The algorithm is an efficient tool with many operational and scientific applications.

Microstructure study of hot rolling nanosized in-situ Al2O3 particle reinforced A356 matrix composites

In this study, A356 matrix and 0.2 vol.%∼0.8 vol.% in-situ Al2O3p/A356 composite were hot rolled to 75% reduction ratio and 0.6 vol.% composite was hot rolled to 75% and 83% reduction ratios. Scanning electron microscope (SEM), electron back scattering diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructure and texture evolution so as to investigate the effect of the particle content and reduction ratios. In the 75% rolling reduction, the Si phase in the A356 matrix and Al2O3p/A356 composites was fragmented and distributed along the rolling direction (RD), obvious Al2O3 agglomeration diminished. On the state of 75% reduction, when the content of Al2O3 was 0.2 vol.%, the composite had the finest grain size, however the 0.6 vol.% composite had a better Si phase and Al2O3 distribution. The Al2O3 particle in 0.2 vol.% sample can enhance the dislocation density and accelerate the sub-grain boundary formation. For the 75% reduction materials, the tensile properties increased with the increase of particulate content to 0.6 vol.% then decreased. The mechanical properties of 83% rolling reduction sample was better than the 75% reduction. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation (El) of 0.6 vol.% Al2O3p/A356 composite increased to 282 MPa, 221 MPa and 17.5%, respectively, due to the uniform distribution of the particles and refined Si phase upon increasing the rolling reduction to 83%, in combination with T4 heat treatment. In addition, the mechanisms of particle dispersion, recrystallization grain refinement and strengthening are also discussed.

Particle dispersion in turbulent, square open duct flows of high Reynolds number

Large eddy simulation is used to study particle dispersion in fully-developed, square open duct flow at Reynolds numbers of 83 k,250 k based on the bulk velocity and duct width. Particle motion is governed by drag, lift, added mass force, pressure gradient force, buoyancy and gravity, with particle size in the range St = 0.032–2415.42. The results show that in the open duct cross-section, secondary flow dominates small particles' dispersion. For larger particles (St > 3.23), gravity plays a significant role in dominating their distribution and deposition rate, which increased with particle size. They tend to disperse better in the spanwise direction than vertical direction. Particles with St = 3.23–96.62 tend to accumulate in the corners, while those with St > 323 in Re = 83 k flow are prone to concentrate in the central regions of duct floor. It is observed that the Reynolds number could enhance particle dispersion in the whole cross-sectional plane. Near the bottom wall, particles with St = 12.93 are found to be also preferentially concentrated by near-wall turbulence, with particle size for this kind of accumulation increasing with Reynolds number. In addition, particles are found to be less dispersed in open duct flow in comparison with closed duct flow. Such trend increases with particle size and dimensionless time. A dynamic force analysis shows that the contribution of pressure drag and lift force gradually increases with particle size. Pressure drag can inhibit particle dispersion, whereas lift force has the opposite effect. The mechanism of particle dispersion in turbulent, open square duct flows is eventually elucidated.

Influence of superplasticiser on cement-stabilised self-compacting earth

Cement-stabilised self-compacting earth (CSCE) is a mixture of soil, water, stabiliser and chemical admixture, with sufficient fluidity to mould earth walls and structures without the need for mechanical densification. The application of the CSCE technology demands a better understanding of the influence of polycarboxylate-based superplasticiser in the mechanisms of particle dispersion, and the microstructure formation of the CSCE. Therefore, for two soil mixtures, sandy soil + cement + water + admixture and clayey soil + cement + water + admixture, the following tests were applied: calorimetry, thermogravimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, compressive strength and water absorption capacity. The results demonstrated that the use of superplasticiser in the CSCE exhibits efficiency of fluidity, mobility, segregation control and exudation control in the mixture. Regardless of the soil type, the influence of the superplasticiser on the CSCE mixtures is more relevant to aspects such as the action of electrostatic dispersion of soil and water and of the particles that induce steric hindrance; also the adsorption reactions of admixture by clay minerals are discrete in the CSCE, resulting in a system with physicomechanical behaviour stabilised and compatible for earth-based construction through the use of superplasticiser in the range of 0·8–1·6 and minimum water/soil ratio with proximity to the liquid limit.

Advanced Metal Matrix Nanocomposites

Lightweight high-strength metal matrix nano-composites (MMNCs) can be used in a wide variety of applications, e.g., aerospace, automotive, and biomedical engineering, owing to their sustainability, increased specific strength/stiffness, enhanced elevated temperature strength, improved wear, or corrosion resistance. A metallic matrix, commonly comprising of light aluminum or magnesium alloys, can be significantly strengthened even by very low weight fractions (~1 wt%) of well-dispersed nanoparticles. This review discusses the recent advancements in the fabrication of metal matrix nanocomposites starting with manufacturing routes and different nanoparticles, intricacies of the underlying physics, and the mechanisms of particle dispersion in a particle-metal composite system. Thereafter, the microstructural influences of the nanoparticles on the composite system are outlined and the theory of the strengthening mechanisms is also explained. Finally, microstructural, mechanical, and tribological properties of the selected MMNCs are discussed as well.

Effects of hot rolling deformation on the microstructure and tensile properties of an in situ-generated ZrB2 nanoparticle-reinforced AA6111 composite

In this study, an in situ-generated ZrB2 nanoparticle-reinforced AA6111 composite was hot rolled to different reduction ratios in the range from 65% to 95% and characterized to observe the microstructural evolution associated with the different rolling states. With increasing rolling reduction, smaller clusters that consisted of many finer spherical ZrB2 nanoparticles were uniformly distributed along the rolling direction (RD). In addition, the uniform distribution and smaller ZrB2 particle accelerated the dynamic recrystallization (DRX) process to further refine the dynamically recrystallized (DRXed) grains. During the hot rolling process, the tensile properties increased with increasing reduction ratio. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation (El) increased to 356 MPa, 289 MPa and 28.1%, respectively, due to the uniform distribution of the particle clusters, the smaller size of the nanoparticles, and the refinement of the DRXed grains upon increasing the rolling reduction to 80%, in combination with T4 heat treatment and artificial ageing. In addition, the mechanisms of particle dispersion, recrystallization grain refinement and strengthening are also discussed.

Particle transport behavior in air channel flow with multi-group Lagrangian tracking**Project supported by the Key Program of the National Natural Science Foundation of China (Grant No. 11132005) and the National Natural Science Foundation of China (Grant No. 50876053).

The particle motions of dispersion and transport in air channel flow are investigated using a large eddy simulation (LES) and Lagrangian trajectory method. The mean and fluctuating velocities of the fluids and particles are obtained, and the results are in good agreement with the data in the literature. Particle clustering is observed in the near-wall and low-speed regions. To reveal the evolution process and mechanism of particle dispersion and transport in the turbulent boundary layer, a multi-group Lagrangian tracking is applied when the two-phase flow has become fully developed: the fluid fields are classified into four sub-regions based on the flow characteristics, and particles in the turbulent region are divided accordingly into four groups when the gas–particle flow is fully developed. The spatiotemporal transport of the four groups of particles is then tracked and analyzed. The detailed relationship between particle dispersion and turbulent motion is investigated and discussed.

A PHYSICAL MODEL OF SEPARATION PROCESS BY MEANS OF JIGS

In the case of ideal separation of minerals, partition into products is conducted according to a specific partition feature which is, for instance, the density of raw material. Usually, enrichment in a jig is described by means of the particle density as a partition feature. However, the degree of particle loosening in the jig's bed is influenced by, among others, the particle free settling velocity. After some time of the pulsating movement duration, particle segregation along the vertical axis according to the settling velocity will occur. It can be said that the particle free settling velocity constitutes a feature characteristic of the feed heterogeneous in terms of physical and geometric properties in the jigging process. In the article on the basis of heuristic considerations, a physical model of the partition function (recovery of the i -th fraction), in which interactions between particles in the working bed of the jig are taken into account, is derived. A cause of the formation of the mechanism of particle dispersion around equilibrium layers is given and the accuracy of particle partition for a narrow size fraction in two variations, i.e. in conditions when a partition feature is, accordingly, the particle density and settling velocity, is calculated. These calculations allowed for the analysis of causes of process and inherent dispersion formation which takes place during the jigging process.

Experimental investigation on the flow characteristics of rice husk in a fuel-rich/lean burner

The particle dispersion mechanisms of rice husk in a fuel-rich/lean burner with an impact-type concentrator were investigated by both digital imaging technique and sampling method. In the experiments, a model burner with a scale ratio of 1/2.708 was studied employing an optical measurement system which consisted of a charge-coupled device (abbreviated as CCD) camera and a laser sheet for illumination. Effects of different impact block heights and inflow particle concentrations on the distribution of rice husk were studied. The distribution of husk particles was obtained by measuring local particle appearance frequency ratio (abbreviated as AFR) within the field of view. Then the size distributions and mass ratios of particles collected from the solid-rich and solid-lean sides were obtained by sampling methods. Increasing the impact block height resulted in a great increase of the rich/lean ratio of particle appearance frequency (abbreviated as RL) at the exit of the burner, as the ratio of 1.66, 5.21 and 9.55 for the block height of 40mm, 50mm and 60mm. Similar tendency was observed when increasing the inflow particle concentration (9.55, 10.57 and 11.87 for 0.1, 0.2 and 0.3kg/kg). The mean size of particles on solid-rich side was always larger as compared with that on the solid-lean side.

Analysis of solid particle clusters in coherent structures of turbulent channel flow

A particle-laden turbulent channel flow is investigated to study particle clusters in large-scale turbulent coherent structures. The fluid phase is calculated by large eddy simulation and particles are tracked using Lagrangian trajectory method. The flow Reynolds number is 180 based on the friction velocity and half-width of the channel. The particle is lycopodium with St=0.93 which may well follow the fluid phase. The mean and fluctuating velocities of both two phases are obtained, which are in good agreement with previous data. The strongest accumulations of particles in low-speed streak structures are observed at y+=11.3. Moreover, once particles are captured in low-speed streaks, most of them will reside there for a long period. Particles clustered in low-speed streaks obtain smaller instantaneous wall-normal and spanwise velocities than those out of there, which induce a larger particle flux into low-speed streaks than that out of there. The study is important for understanding particle dispersion mechanisms in gas-particle turbulent channel flows.

Analysis of Inertial Particle Drift Dispersion by Direct Numerical Simulation of Two-Phase Wall-Bounded Turbulent Flows

This paper analyzes inertial particle drift dispersion based on the numerical database established by direct numerical simulation of a dilute particle-laden two-phase turbulent channel flow, in which the released particles are tracked by a Lagrangian trajectory method. Low-inertia particles tend to travel toward the walls at negative velocities. High-inertia particles however display very low drift in the near-wall regions. Effects of particle size and material density on particle drifts are also jointly studied. The statistical results show that particles drift dispersion depends significantly on particle Stokes number. Low-inertia particle drift dispersion causes a direct low-inertia particle deposition on the wall, and hence increases the particle concentration close to the walls. The results are valuable for understanding the mechanisms of particle dispersion by turbulence.

DEM–CFD simulation of the particle dispersion in a gas–solid two-phase flow for a fuel-rich/lean burner

The objective of this study was to numerically investigate the particle dispersion mechanisms in the gas–solid two-phase jet for a fuel-rich/lean burner by means of coupling the discrete element method (DEM) with the computational fluid dynamics (CFD). The DEM was employed to deal with the particle–particle and the particle–wall interaction in the computation of solid flow; while gas flow was computed by CFD based on the commercial software package Fluent. The particles with various Stokes numbers equal to 0.1, 0.5, 1, 2 and 3 (corresponding to particle diameter 10.8, 24.17, 34.18, 48.38 and 59.21μm, respectively) in the gas–solid fuel-rich/lean jet were investigated in this study. The particle–particle collision was simulated and its effect on the fuel-rich/lean separating performance was evaluated. The results show that the particle–particle collision occurred more frequently with the increasing of Stokes numbers from 0.1 to 3. The particle dispersion became more uniform between the fuel-rich side and the fuel-lean side for particles with small Stokes number; while for particles at St>1, a better fuel-rich/lean separating performance was achieved. The efficiency of the DEM–CFD coupling method was validated by the corresponding experiments, and a good agreement between the simulation and experiments was achieved as a result of the particle–particle collision.

Mechanisms of particle dispersion in a turbulent, square duct flow

AbstractParticle dispersion in a square duct flow is studied using large eddy simulation combined with Lagrangian particle tracking under conditions of one‐way coupling. The flow has a bulk Re = 250 k, with six particle sizes ranging from 5 to 1000 μm. Results obtained for the fluid phase show good agreement with experimental data. For particles, predictions demonstrate that secondary flows within the duct dominate small particle dispersion and result in a uniform distribution, whereas gravity promotes the deposition of large particles on the duct floor. For the largest particles, the secondary flows contribute to particle concentration in corners on the duct floor, with these particles also clustering in low‐velocity regions close to the floor. A detailed analysis of the influence of the flow on particle distribution is provided through consideration of the particle dispersion function, with the mechanisms of particle dispersion elucidated using a dynamical analysis. © 2009 American Institute of Chemical Engineers AIChE J, 2009

自熔炉の精鉱バーナー内の精鉱粒子の分散挙動に関する数値的研究

The smelting performance of a flash smelting furnace in the copper smelting process depends on the efficient premixing of concentrate particles and reaction air in the concentrate burner. When the concentrate particles and reaction air in the burner are well-premixed, the flowing pressure shows an additional pressure drop due to the interaction between the particles and the gas flow. In this study, the flow profile of the reaction air and the dispersion behavior of the concentrate particles in the concentrate burner are simulated by using numerical models in order to reveal the particle dispersion mechanism in the reaction air. When the concentrate particles are not fed into the burner, the reaction air mainly flows down along the inner wall of the burner cone and a large circulation flow is formed inside the main flow. The upward flow of the circulation flow formed below the concentrate chute prevents the concentrate particles fed through the chute from flowing down in the axial direction, and the particles consequently spread in the radial direction.

Application Of Power Ultrasound For Nano-Particle Size Reduction Of Active Pharmaceutical Ingredients

Properties of drug substances and dosage forms can be highly affected by the particle size, a critical process parameter in pharmaceutical production. The fundamental issue with particle size analysis is the variety of equivalent particle diameters generated by different methods, which is largely ascribable to the particle shape and particle dispersion mechanism involved. Thus, to enable selection of the most appropriate or optimal sizing technique, cross-correlation between different techniques may be required. This review offers an in-depth discussion on particle size analysis pertaining to specific pharmaceutical applications and regulatory aspects, fundamental principles and terminology, instrumentation types, data presentation and interpretation, in-line and process analytical technology. For illustration purposes, special consideration is given to the analysis of FXD.