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41.
42.
This paper describes the formulation of a quasi-1-D network model, referred to as the ‘bubble model’, and its application
for simulating particle transport and filtration through a granular filter bed. The model comprises a series of homogeneous
sites linked through bundles of cylindrical bonds that represent flow pathways through distributions of pores and pore throats.
This model incorporates pore scale processes of particle sieving and infiltration are based on numerical simulations described
in a companion paper. The modeling of infiltration is further refined based on detailed experimental observations and measurements
of the filtration of a dilute suspension of acrylic particles through a column of glass beads reported by Yoon et al. (2005 Water Resour. Res., to appear). Their data distinguish (a) between the collection of particles on grain surfaces and at grain-to-grain contact
points, and (b) between particles that are fully entrapped and those that are hindered (temporarily collected) and can later
become detached. These effects are represented by two parameters that characterize the probability of attachment and are linked
to the surface roughness of the grains; one that describes the minimum particle size that can be fully entrapped, and one
that describes the detachment rate. These parameters can be readily calibrated from conventional measurements of effluent
concentration and effluent particle size distribution. Detailed comparisons with the data reported by Yoon et al. show that the proposed bubble model is able to achieve reliable predictions of the spatial distribution of particles within
the filter bed following phases of particle injection and washing. 相似文献
43.
经固溶处理的A1-Cu—Mg合金在常应变率拉伸实验中具有显著的锯齿形屈服现象,且屈服行为随固溶处理温度的改变而呈现不同的特征。塑性变形特性与合金材料的微细观结构,尤其是位错运动的演化密切相关。本文运用透射电子显微镜,研究在不同温度下固溶处理的Al—Cu—Mg合金的微观结构,尤其是析出颗粒的大小和含量。并结合宏观的拉伸实验结果,分析Al—Cu—Mg合金动态应变时效的机制。 相似文献
44.
王柏懿 《应用数学和力学(英文版)》2003,24(8):928-935
By using Lagrangian method, the flow properties of a dusty-gas point source in a supersonic free stream were studied and the particle parameters in the near-symmetry-axis region were obtained . It is demonstrated that fairly inertial particles travel along oscillating and intersecting trajectories between the bow and termination shock waves . In this region, formation of " mufti- layer structure" in panicle distribution with alternating low- and high density layers is revealed. Moreover, sharp accumulation of particles occurs near the envelopes of particle trajectories . 相似文献
45.
YuchengWu YongZhang LideZhang 《中国颗粒学报》2004,2(1):19-24
Nanosized palladium particles were incorporated into mesoporous silica matrix to obtain nanocomposites using the sol-gel technique. Effects of the finely dispersed metallic palladium on the microstructure and properties of the nanocomposites were investigated. By means of X-ray diffraction and optical absorption, it was found that palladium particles were 5-9 nm in diameter and their uniform dispersion in the mesoporous silica depended on both the content of the palladium and the structural features of the silica matrix. The results showed that the mixing method of preparation led to wider size distribution of the nanosized particles as compared to the immersion method, but dispersed degree was reduced. Although the incorporation of nanosized palladium particles could not substantially induce significant structural changes of the matrix, the apparent red-shifted optical absorptions for the nanocomposites were observed as compared to the parent monolithic silica, particularly with increase in palladium loading and calcination temperature. 相似文献
46.
JieLi J.A.M.Kuipers 《中国颗粒学报》2004,2(1):1-12
The occurrence of heterogeneous flow structures in gas-particle flows seriously affects the gas-solid contacting and transport processes in high-velocity gas-fluidized beds. Particles do not disperse uniformly in the flow but pass through the bed in a swarm of clusters. The so-called “core-annulus“ structure in the radial direction and “S“ shaped axial distribution of solids concentration characterize the typical flow structure in the system. A computational study, using the discrete particle approach based on molecular dynamics techniques, has been carried out to explore the mechanisms underlying formation of the clusters and the core-annulus structure. Based on energybudget analysis including work done by the drag force, kinetic energy, rotational energy, potential energy, and energy dissipation due to particle-particle and particle-wall collisions, the role of gas-solid interaction and inelastic collisions between the particles are elucidated. It is concluded that the competition between gas-solid interaction and particle-particle interaction determines the pattern formation in high-velocity gas-solid flows: if the gas-solid interaction (under elevated pressure) dominates, most of particle energy obtained by drag from the gas phase is partitioned such that particle potential energy is raised, leading to a uniform flow structure. Otherwise, a heterogeneous pattern exists, which could be induced by both particle -particle collisions and gas-solid interaction. Although both factors could cause the flow instability, the non-linear drag force is demonstrated to be the necessary condition to trigger heterogeneous flow structure formation. As gas velocity increases and goes beyond a critical value, the fluid-particle interaction suppresses particle collisional dissipation, and as a consequence a more homogeneous flow regime is formed. 相似文献
47.
Antoine Sellier 《Comptes Rendus Mecanique》2003,331(6):401-406
Particle–boundary and particle–particle interactions in Electrophoresis are examined by considering a 2-particle cluster near a plane boundary. The advocated treatment holds for two insulating particles of arbitrary shapes and zeta potential functions and resorts to 13 boundary-integral equations. Preliminary results reveal that, depending upon the addressed velocity nature (translational or angular), wall–particle may be stronger or weaker than particle–particle interactions. To cite this article: A. Sellier, C. R. Mecanique 331 (2003). 相似文献
48.
Ali Gooneie Stephan Schuschnigg Clemens Holzer 《Macromolecular theory and simulations》2016,25(2):170-186
Polydisperse linear polymers are studied in startup of steady shear flow simulations using dissipative particle dynamics. The results show that with an increase in polydispersity the stress overshoot declines while the steady‐state stress increases. Various physical characteristics of the systems are studied including frequency of nonbonded interactions, gyration radius data, flow alignment angles, and average bond lengths. The patterns in the data suggest higher forces are necessary to orient and stretch long chain fractions in the flow direction. Relaxation modulus data prove the broad range of relaxation mechanisms in polydisperse systems. Linear viscoelasticity theory is used to quantify the relaxation spectrum. The results indicate an increase in the longest relaxation time in systems with higher polydispersity. The steady‐state shear viscosity results show higher viscosities with an increase in polydispersity at all shear‐rates. The good agreement of the characteristic behaviors of modeled polydisperse polymers with experiments is encouraging for future work.
49.
A Cu-TiC alloy, with nanoscale TiC particles highly dispersed in the submicron-grained Cu matrix, was manufactured by a self-developed two-step ball-milling process on Cu, Ti and C powders. The thermostability of the composite was evaluated by high-temperature isothermal annealing treatments, with temperatures ranging from 727 to 1273 K. The semicoherent nanoscale TiC particles with Cu matrix, mainly located along the grain boundaries, were found to exhibit the promising trait of blocking grain boundary migrations, which leads to a super-stabilized microstructures up to approximately the melting point of copper (1223 K). Furthermore, the Cu-TiC alloys after annealing at 1323 K showed a slight decrease in Vickers hardness as well as the duplex microstructure due to selective grain growth, which were discussed in terms of hardness contributions from various mechanisms. 相似文献
50.