Particle Distribution State Research Articles

Flow visualization simulation of cemented tailings backfill slurry by particle tracking technology

AbstractPipeline flow visualization of cemented tailings backfill slurry (CTBS) improves the safety and stability of transportation. High turbidity and low resolution make it difficult for conventional methods to monitor the particle distribution state of CTBS in a short period of time. Particle tracking technology (PTT) is used to simulate and investigate the flow characteristics of CTBS pipeline, combine with theoretical analysis to construct a CTBS pipeline visualization model, elaborate the particle distribution state when CTBS flows in the pipeline, and explore the effects of pipe diameter (PD), flow velocity (FV) and tailings gradation (TG) on the particle distribution. The results show that particle tracking technology is better applied to investigate the particle transport distribution characteristics of CTBS tailings. Three concepts of particle accumulated gravity Ga, static friction angle θ and diameter dividing line are defined, and the transport pipe is divided into light wear zone, medium wear zone and heavy wear zone. The increase in pipe diameter increases the content of fine particles at the pipe wall and the thickness of the lubrication layer becomes larger, which improves the safety and stability of CTBS transport. The increased flow velocity reduces the settling phenomenon of large size particles and improves the transport efficiency, which increases the pipeline transport resistance. Under good tailings grading conditions, a wide range of tailings grading is more suitable as backfill material. The results of the study illustrate the flow characteristics of the backfill slurry in the pipeline from the particle perspective and provide a theoretical basis for pipeline transportation research.

Size Distribution Analysis of the Adeno-Associated Virus Vector by the c(s) Analysis of Band Sedimentation Analytical Ultracentrifugation with Multiwavelength Detection

Adeno-associated virus (AAV) vector is a promising platform for in vivo gene therapy. The accurate assessment of distribution state of particles contained in AAV vector samples is one of the most important and challenging matters and is necessary because the product-related impurities with the capsid structure (empty particles, intermediate particles, and aggregates) could be a possible cause of reducing the therapeutic efficacy and enhancing the unfavorable immune response. In this study, we report an effective approach for size distribution analysis with component identification. A small amount of AAV vectors were used by the analytical zone centrifugation c(s) analysis of band sedimentation analytical ultracentrifugation (BS-AUC) with multiwavelength detection. Using PBS/H218O, the concentration of each component could be determined in BS-AUC with high resolution. Compared with the sedimentation velocity AUC (SV-AUC), which generally requires 2 × 1012 vg of AAV vectors, BS-AUC could be performed with about 1/25 of the AAV vector amount at 260 nm detection and ideally with about 1/50 of the AAV vector amount at 230 nm detection (4 × 1010 vg), depending on the extinction coefficient of the AAV sample at each wavelength. According to the limit of quantification of this BS-AUC, 6.3 × 1011 cp mL−1 of empty particle (EP) and 4.4 × 1011 vg mL−1 of full particle (FP) could be quantified for 4 × 1010 vg in 15 µL of AAV8-CMV-EGFP. These results demonstrated that proposed BS-AUC approach we established here can compensate for the drawback in terms of the sample amount of SV-AUC.

Investigation into the Mechanism of the Steel Particle Feeding Process: A Numerical and Experimental Study

The particle feeding system is a prerequisite for the realization of particle impact drilling technology. Because of the high density, the storage and flow of the steel particle are different from those of the other nonviscous particles. The differential equation of the particle movement was built with the liquid bridge force model and the discrete element method. The dynamic movement process and the distribution state of particles in the high-pressure tank were analyzed. For 1 mm steel particles, the mass flow rate decreased with the increase in water content. For 2 mm and 3 mm steel particles, the water content of 15% and 20% was the dividing point of the mass flow rate from increasing to decreasing. When the water content was 10% and 20%, the mass flow rate increased with the steel particle size. But when the water content was 30% and 40%, the mass flow rate decreased with the steel particle size. The study of the control mechanism of the uniformity and stability of particles showed that the funnel flow was the major reason causing the instability and blocking of the feeding process. This research results can provide a basis for the further improvement of the differential pressure feeding system.

Development of air pressure mirroring particle dispersion method for producing high-density tungsten medical radiation shielding film

Radiation shielding films used in medical institutions are manufactured by mixing polymer materials with eco-friendly shielding materials. However, it is not easy to distribute the shielding material particles uniformly during the process. The uniform distribution of the shielding material particles is key to the reproducibility of the shielding performance of the films. Therefore, in this study, an air pressure mirroring particle dispersion method was developed to maintain a uniform distribution of the shielding material by dispersing the shielding material on a curved reflector through an air nozzle. The particle distribution state, density, and shielding performance of the cross-section and surface of the shielding films developed using the single-sided dispersion, double-dispersion, and air pressure mirroring particle dispersion methods were evaluated. Compared to the conventional single-sided distribution method, the shielding film produced by the air pressure mirroring particle dispersion method increased the particle packing by 41.5%, density by 12.9%, shielding material content by 22.2%, and shielding performance by 21.4%. Thus, the proposed dispersion method enables better shielding performance through uniform dispersion of shielding material, which is the most important parameter in the manufacture of low-dose shielding films.

Thermal conduction of the magnetic fluids mixing micrometer size particles

In this study, thermophysical properties of magnetic fluids mixing micrometer size spherical copper particles were investigated experimentally. To examine the behavior of dispersed micrometer size copper particles in the magnetized magnetic fluid, visualization experiments were performed by using a dark field microscope. From the visualization experiments, cluster formations of the copper particles in the magnetic field direction in the magnetic fluid under applied uniform magnetic field were observed. The thermal conductivity of the test fluid was measured by using the transient hot wire method. Thermal conductivity of the magnetic fluid with randomly dispersing copper particles is larger than the thermal conductivity of the base magnetic fluid. In case of the magnetic fluid mixed 12 vol% of spherical copper particles, it was estimated that the thermal conductivity in the field direction increases by 1.7 times or more of the thermal conductivity of the fluid in the absence of magnetic field. The Landau-Lifshitz equation for estimating the relationship between the thermal conductivity and the internal structure was expanded to consider spherical shape of the dispersed particles in the fluid and the particle distribution state was estimated by using the expanded Landau-Lifshitz equation.

Selective laser melting of TiN nanoparticle-reinforced AlSi10Mg composite: Microstructural, interfacial, and mechanical properties

Abstract TiN nanoparticle reinforced AlSi10Mg composite powder was produced by a novel ultrasonic vibration dispersion technique. The TiN/AlSi10Mg composites were fabricated via selective laser melting (SLM). The effects of scanning speed on the microstructure, particle distribution state, and tribological properties of the as-built composites were studied. Experimental results showed a better SLM processibility for the composite powder due to the considerable improvement of laser absorption capacity. The microstructure of as-built composite parts was remarkably refined with a gradually decreased average grain size from 0.388 μm to 0.284 μm by increasing scanning speed compared to that of AlSi10Mg part (∼ 0.579 μm). Nano-sized TiN particles were evenly distributed and well-bonded in the composite matrix while minimized agglomerated TiN particles gathered and grew into large spherical clusters. Because of the in-situ reaction occurred between TiN cluster and AlSi10Mg matrix, novel graded interfacial layers were observed. The mean layer thickness increased from 0.11 μm to 0.38 μm by decreasing the scanning speed from 600 mm/s to 200 mm/s. Taking advantage of the dispersion strengthening, fine grain strengthening, and the graded interfacial layer, a considerably-high microhardness (145 ± 4.9 HV), and enhanced wear performance were achieved.

The Depolarization Performances of the Polarized Light in Different Scattering Media Systems

In this paper, with the aids of the Monte Carlo simulations, we have investigated the depolarization performances of circularly polarized light (CPL) and linearly polarized light (LPL) transmitted in homogeneous scattering media systems. The depolarization performances depend on the number density, refractive index, and the concrete size distributions of scattering particles. Here, we mainly investigate the mixed ratio and distribution effect of scattering particles on the depolarization performances of CPL and LPL, respectively. The simulation results show that there exist larger mismatches in the depolarization performances between monodisperse and polydisperse scattering systems, and with increasing small particles' proportion the degree of linear polarization decreases slightly, but the degree of circular polarization decreases drastically. When the size distribution of scattering particles obey the logarithmic normal distribution, the simulated results show that the propagation behavior of the incident light in a polydisperse medium system with standard deviation of σ = 0.1 μm can be modeled very well by the corresponding monodisperse medium system with the mean value, however, the approximation will fail for a scattering medium with larger standard deviation of σ = 0.5 μm. These results demonstrated that the depolarization behavior of light was sensitive to the mixed ratio or the distribution state of particles, which was significant to the polarization engineering, such as polarization imaging and polarization based communications.

Visual Attention Model Based on Particle Filter

The visual attention mechanism includes 2 attention models, the bottom-up (B-U) and the top-down (T-D), the physiology of which have not yet been accurately described. In this paper, the visual attention mechanism is regarded as a Bayesian fusion process, and a visual attention model based on particle filter is proposed. Under certain particular assumed conditions, a calculation formula of Bayesian posterior probability is deduced. The visual attention fusion process based on the particle filter is realized through importance sampling, particle weight updating, and resampling, and visual attention is finally determined by the particle distribution state. The test results of multigroup images show that the calculation result of this model has better subjective and objective effects than that of other models.

Formation of novel graded interface and its function on mechanical properties of WC1−x reinforced Inconel 718 composites processed by selective laser melting

Selective laser melting (SLM) additive manufacturing (AM) process was applied to produce WC1−x particle reinforced Inconel 718 composite parts. The effects of the applied laser energy linear density (η) on the densification behavior, particle distribution state and the microstructure of the WC1−x/Inconel 718 composite parts were deeply researched in this paper. According to the experimental results, a η of 303 J/m resulted in a nearly full dense part with a uniform distribution of the WC1−x reinforcing particles owing to sufficient melting of mixed powder and rearrangement of the WC1−x particles. Due to an in situ reaction between the reinforcing particle surfaces and Inconel 718, a graded interfacial layer with a composition of (W, M)C3 (M = Ni, Cr, Fe) was tailored between the reinforcing particles and the matrix during the SLM processing. Meanwhile, a category of diffusion layer between the graded interfacial layer and the matrix with a composition of (W, M)C2 (M = Ni, Cr, Fe, Nb) was found, showing a slight increase amount of Ni, Cr, Fe and decrease of W and C as well as an additional strong carbide-forming element Nb. At an optimal η of 242 J/m, a considerably high microhardness of 389.4 HV0.1 and a considerably low coefficient of friction (COF) of 0.39 and resultant low wear rate of 2.3 × 10−4 mm3 N−1 m−1 were realized due to the united strengthening of the graded interfacial layer and the (W, M)C2 diffusion layer. A comprehensive relationship between densification behavior, microstructure and wear performance of the SLM-processed WC1−x/Inconel 718 composite parts was discussed.

TiO2아나타제에 대한 고압 상변이 연구

<TEX>$TiO_2$</TEX>의 동질이상체 중 하나인 아나타제는 고압 하에서 결정의 크기와 모양에 따라 다른 상변이 경로를 보이는 것으로 알려져 있다. 본 실험에 이용된 아나타제 분말시료는 15~25 nm 정도 크기의 입자로 구성되어 있으며, 고압라만분광분석 결과와 고압 X-선회절실험결과 분석을 종합하면 20 GPa 이상의 압력에서 비정질로 상변이하는 것으로 관찰되었다. 상온에서 압력의 영향으로 상변이한 비정질 구조는 압력을 제거하여도 출발 결정구조로 회귀하지 않는 것으로 밝혀졌다. 이 결과는 베델레이트로 상변이하는 이전의 결과와 상치되며, 출발시료 구성입자의 분급상태가 입자의 불안정성에 영향을 끼쳐 최종적으로 비정질화에 기여한 것으로 판단된다. Anatase, one of the <TEX>$TiO_2$</TEX> polymorphs, is known to show different phase transition paths depending on its crystalline and shape. Particle size of 15~25 nm anatase has been subjected to high-pressure Raman spectroscopy and X-ray diffraction studies using a diamond anvil cell. We observe that the starting sample transforms to an amorphous phase above approx. 20 GPa, which is retained upon pressure release to ambient condition. This is in contrast to previously established transition to baddeleyite phase and we suspect difference in the particle distribution state trigger phase instability of nanoparticles and hence amorphization.

Preparation, Particle Characterizations and Application of Nano-Pigment Suspension

In this work, we focus on preparation of nano-suspension of organic pigment for different milling method to discuss optimum formula, milling effect, particle characterizations (particle size, sedimentation velocity and stability) by analytical centrifugation system. Due to the variation of centrifugal force, time scales and space variations occur in the suspension such that during the migration of particles, the light transmission, and the vanishing coordinates are plotted on a profile. Therefore, objective of the article was evaluated to predict the particle characterizations between the particle distribution state and long-term stability as accelerated test during centrifugation. Besides, we were also used to observe nano-suspension of organic pigment the mean size, aggregation phenomena and dispersibility of the pigment particles by SEM and TEM. Additionally, we applied to manufacture the LCD-based blue filter and discussed performance of the blue filer by transmission of UV light, color evolution and adhesion ability assessments in this study.

Characterization of the spatial distribution state of particles transported by a turbulent gas flow

A concept is presented for the characterization of the spatial arrangement of particles dispersed in fluids. Exact knowledge of the spatial distribution state of dispersed phases is very useful for many chemical engineering processes. A suitable characterization is done by means of computing the frequency distributions of distances between neighbouring particles. The computation is accomplished on the basis of data obtained by hologram evaluation. Measurements were conducted via pulsed-laser holography. The examples described concern collectives of water droplets and glass spheres transported by a turbulent gas flow through a pipe. The experimental results are compared with theoretically obtained frequency distributions of particle distances for particles arranged in space purely at random.