Dispersion Behavior Of Particles Research Articles

Dispersion Behavior of Coarse Particles by Lateral Vibration under Microgravity [Translated]<sup>†</sup>

Dispersion Behavior of Coarse Particles by Lateral Vibration under Microgravity [Translated]<sup>†</sup>

An explanation of distance‐dependent dispersion of mass transport in fractured rock

This paper presents a stochastic, discrete fracture model to investigate the distance‐dependent dispersion phenomenon in fractured rock. Under imposed boundary conditions, the dispersion behavior of particles is observed. Simulated results demonstrate that the coefficient of anisotropic dispersion tensor increases with an increasing traveled distance. The anisotropic ratio of dispersion tensor is small and almost increased linearly with migration distance at early migration. The anisotropic ratio has the trend to maintain constant or small variation after a specifietl migration distance. It was also noted that the plume of particles is elliptic.

Particle behavior in a two-fluid turbulent plasma jet

This paper is concerned with the application of a two-fluid turbulence model for plasma spray processes at atmospheric pressure, for improving our physical insight into the plasma/particle interactions. In this two-fluid turbulence model, the turbulent stream is treated as a two-phase mixture. The fluid parcels are assumed to be arranged in fragments, and they can exchange mass, momentum, and other properties. A stochastic approach is then used to study particle behavior under the influence of the two-fluid parcels. The Stokes number is introduced as an indicator of particle dispersion behavior. A series of simulations is performed to include the influence of different injection locations, particle sizes, and injection velocities. The results indicate the importance of the existence of large-scale eddies and variable property, Knudsen, and mass-transfer cooling effects on the particle motion and heating history.

Characterization of particle-laden, confined swirling flows by phase-doppler anemometry and numerical calculation

The particle dispersion characteristics in a confined swirling flow with a swirl number of approx. 0.5 were studied in detail by performing measurements using phase-Doppler anemometry (PDA) and numerical predictions. A mixture of gas and particles was injected without swirl into the test section, while the swirling airstream was provided through a co-flowing annular inlet. Two cases with different primary jet exit velocities were considered. For these flow conditions, a closed central recirculation bubble was established just downstream of the inlet. The PDA measurements allowed the correlation between particle size and velocity to be obtained and also the spatial change in the particle size distribution throughout the flow field. For these results, the behaviour of different size classes in the entire particle size spectrum, ranging from about 15 to 80 μm, could be studied, and the response of the particles to the mean flow and the gas turbulence could be characterized. Due to the response characteristics of particles with different diameters to the mean flow and the flow turbulence, a considerable separation of the particles was observed which resulted in a streamwise increase in the particle mean number diameter in the core region of the central recirculation bubble. For the lower particle inlet velocity (i.e. low primary jet exit velocity), this effect is more pronounced, since here the particles have more time to respond to the flow reversal and the swirl velocity component. This also gave a higher mass of recirculating particle material. The numerical predictions of the gas flow were performed by solving the time-averaged Navier-Stokes equations in connection with the well known kϵ turbulence model. Although this turbulence model is based on the assumption of isotropic turbulence, the agreement of the calculated mean velocity profiles compared to the measured gas velocities is very good. The gas-phase turbulent kinetic energy, however, is considerably underpredicted in the initial mixing region. The particle dispersion characteristics were calculated by using the Lagrangian approach, where the influence of the particulate phase on the gas flow could be neglected, since only very low mass loadings were considered. The calculated results for the particle mean velocity and the mass flux are also in good agreement with the experiments. Furthermore, the change in the particle mean diameter throughout the flow field was predicted approximately, which shows that the applied simple stochastic dispersion model also gives good results for such very complex flows. The variation of the gas and particle velocity in the primary inlet had a considerable impact on the particle dispersion behaviour in the swirling flow and the particle residence time in the central recirculation bubble, which could be determined from the numerical calculations. For the lower particle inlet velocity, the maximum particle size-dependence residence time within the recirculation region was considerably shifted towards larger particles.

ＳｉＣｐ／Ａｌ‐Ｔｉ合金溶湯間反応によるｉｎ ｓｉｔｕＴｉＣｐ／アルミニウム複合材料の製造と機械的性質

A novel technique has been developed for fabricating in situ formed TiCp/Al composites. In this process, fairly stable TiC particles were in situ synthesized in liquid aluminum by the interfacial reaction between an Al-Ti melt and SiC, which is a comparatively unstable carbide from the view-point of thermodynamics. It is possible in the present process to generate TiC particles of nearly 1μm in diameter, even utilizing SiC of 14μm as raw material. However, the dispersion behavior of TiC particles in the matrix depends on the size of the raw material SiC. Decomposing finer SiC makes the dispersion of_TiC particles more uniform and the mechanical properties of composites are improved accordingly. The structure of in situ composites and their mechanical properties are affected by the fabrication temperature and the stirring time. It has been found that the most suitable condition for fabrication should be applied depending on the size of the raw material, even if the same kinds of carbide are used. Furthermore, although Al-Ti-Si system intermetallic compounds were detected in a TiCp/Al-Si composite which was fabricated by conventional melt stirring method, these compounds can not be observed in a TiCp/Al-Si composite made by this in situ production method. Hence, the mechanical properties of the in situ TiCp/Al-Si composite are superior to those of the conventional TiCp/Al-Si composite.

溶融アルミニウム中における炭化物粒子の<I>in situ</I>生成挙動

The in situ formation and dispersion behavior of carbide particles in a liquid aluminum alloy has been investigated to develop a novel technique utilizing the spontaneous reaction among materials for fabricating aluminum matrix composites. Titanium, zirconium and hafnium carbide were in situ generated by the reaction between a liquid aluminum alloy containing the group IVa element and Al4C3 particles. However, the reaction rate decreased in the order of titanium, zirconium and hafnium. On the other hand, the amount of in situ formed carbide in the aluminum alloy system containing group Va element increased in the order of vanadium, niobium, tantalum depending on the thermodynamical stability of the carbide of each element.The effects of processing variables, such as the kind and size of raw carbide, the alloying element and processing temperature on the in situ formation rate of TiC and ZrC have been estimated quantitatively. The experimental results were analyzed by the in situ reaction kinetic model based on the assumption that the overall reaction rate was controlled by both the interfacial reaction and the diffusion through the layer of the generated carbide particles. At the initial stage of the formation of TiC, the interfacial reaction rate is mainly controlling step. However, the process is gradually controlled by the diffusion at the later stage. Owing to the formation of fine circular carbide surrounding raw carbide particles, the in situ reaction rate decreased radically in the Al-Zr or Al-Hf system.

On the dispersion of SiCAl slurries in rotating flows

An experimental study was conducted to determine the role of fluid flow on dispersion of SiC particles in molten aluminum. In this work, slurries containing up to 18 vol.% SiC were dispersed in rotational Couette flow at high shear rates ranging from 50 to 500 s −1. The relative viscosity of SiCAl metal matrix composite slurries was also measured. It was found that the particles were uniformly dispersed in the radial direction. No particle agglomeration was observed. Axial dispersion was found to occur under certain stirring conditions. A particulate dispersion number PD based on stirring parameters and particle-settling velocity was developed to describe the dispersion behavior of particles in rotating fluids. The measured viscosities of the SICAl slurries investigatedwere found to be in good agreement with Einstein's equation.

Studies on the distribution and polycyclic aromatic hydrocarbons of particulate substances in the vicinity of an expressway. Rep. 2. Properties of diffusion of particulate substances.

In order to clarify the dispersion properties of suspended particulate matter (SPM) in the vicinity of the Meishin expressway, a) the relationship between SPM concentration and the traffic volume of each type of automobile was studied, b) the density distribution of each size of particle was compared with that of nitrogen dioxyde (NO2), Which was the most representative gaseous pollutant from mobile sources, and c) the actual concentrations of particles were compared with the concentrations calculated by the Tokyo Metropolitan Government (TMG) dispersion model in which the effect of gravity on the particles was included. The results were as follows;1) A statistically significant and positive correlation were shown only between the traffic volume of large vehicles and the concentrations of fine particles under 1.6μm.2) At all the measured points, fine particles under 0.7μm in diameter accounted for 44.8% to 65.8% of the total SPM. It was observed that these particles showed a distinct concentration-distance profile with the increase of the average wind velocity.3) As the particle size became smaller, the correlation coefficient between the concentrations of particles and NO2 concentrations became larger. In the case of fine particles under 5.4μm in diameter, the coefficient of correlation was extremely high and was statistically significant.4) In the case of fine paricles under 5.4μm in diameter, the coefficient of correlation between the measured and calculated concentration of each size of particle was extremely high and was statistically significant. In accordance with the facts described above, it was suggested that the dispersion behavior of fine particles under 1.6μm could be well explained in the same manner as gaseous pollutants, and it was proved that these particles were derived from large vehicles with diesel engines.