Particle migration of concentrated suspension flow in bifurcating channels

Flow of suspension in bifurcating channels has extensive applications in industrial and natural settings. A phenomenon of particular interest during the flow of concentrated suspension is shear-induced particle migration. Previous works on suspension transport in branched channels have been limited to dilute flow conditions. We have carried out experiments using the Particle Image Velocimetry (PIV) technique to study concentrated suspension transport in asymmetric T- and symmetric Y-shape channels. Numerical simulations of fluid flow and particle transport equations were also carried out for the same geometry which was used in the experiments. The migration and transport of particles in the simulations were studied using the Diffusive Flux Model. We have observed in both experiments and numerical simulations that due to the shear-induced migration phenomena the particles move towards the center of the channel, and this gives rise to the blunting of velocity profile before the junction. After the bifurcation, the peak of velocity profile moves in the direction of the outer wall, whereas, the maxima in particle concentration was observed near the inner walls. This causes asymmetry in the velocity and concentration profiles in the daughter branches. As we move towards the downstream positions the maxima in velocity and concentration profiles again shifts toward the center of the channel. The results from the experiments and simulations are observed to be in good agreement.     

悬索桥主缆缠丝涂装防护

主缆是悬索桥的主要承重受力构件。主缆由高强度镀锌钢丝组成。由于处在跨江、跨海的环境中,主缆可能产生腐蚀。为了保证悬索是安全用使用寿命,必须对主缆进行特殊涂装保护。结合国内已建成的几座特大型悬索桥主缆防护工程,介绍几种主缆缠丝、涂料涂装方案,并对其特点进行分析讨论。     

CMAS corrosion of YSZ thermal barrier coatings obtained by different thermal spray processes

Degradation of yttria-stabilized zirconia (YSZ) layers by molten CaO-MgO-Al₂O₃-SiO₂ (CMAS)-based deposits is an important failure mode of thermal barrier coating (TBC) systems in modern gas turbines. The present work aimed to understand how the chemical purity and microstructure of plasma-sprayed YSZ layers affect their response to CMAS corrosion. To this end, isothermal corrosion tests (1 h at 1250 °C) were performed on four different kinds of YSZ coatings: atmospheric plasma-sprayed (APS) layers obtained from standard- and high-purity feedstock powders, a dense – vertically cracked (DVC) layer, and a suspension plasma sprayed (SPS) one. Characterization of corroded and non-corroded samples by FEG-SEM, EBSD and micro-Raman spectroscopy techniques reveals that, whilst all YSZ samples suffered grain-boundary corrosion by molten CMAS, its extent could vary considerably. High chemical purity limits the extent of grain-boundary dissolution by molten CMAS, whereas high porosity and/or fine crystalline grain structure lead to more severe degradation.     

ACS树脂的合成与性能研究

从丙烯腈－氯化聚乙烯－苯乙烯（ＡＣＳ）三元悬浮共聚的技术特点出发,分别研究了氯化聚乙烯用量、苯乙烯／丙烯腈之比、聚合时间对聚合工艺对产物性能的影响,并在此基础上考察了引发剂体系的影响,确定了适宜的引发剂种类及用量。     

Microstructures of nanostructured ceramic coatings obtained by suspension thermal spraying

In the present work, the elaboration of nanostructured alumina and titania coatings by thermal spraying with liquid precursors is described. Nano- and submicrometer-sized powders were used to prepare aqueous or alcoholic suspensions. The suspensions were sprayed using APS and HVOF processes in order to obtain thin and thick deposits. The paper discusses the coating microstructures as a function of suspension characteristics and spray parameters in both APS and HVOF processes.     

Non-linear shape-finding analysis of a self-anchored suspension bridge

A non-linear shape-finding analysis is proposed for a self-anchored suspension bridge, the Yongjong Grand Bridge, the main cable of which is three-dimensional in shape. The proposed procedure consists of two successive steps of non-linear analysis. The first step focuses on the cable-only system and the second on the total bridge system. A trial profile of a three-dimensional main cable was calculated based on the conventional method utilizing a simplified force equilibrium at each node of the main cable. The non-linear analysis is then repeated for this cable-only system until the profile converges to the target configuration that satisfies the vertical design sag at the mid-point of the main span. Even when the best efforts were made to determine the configuration of the cable-only system, the initial deformation of the stiffening truss is not avoidable due to the huge axial force that originates from the main cable. Therefore, the initial frame forces are predicted and included in calculating the unbalance loads for the non-linear analysis of the total bridge system so as to prevent dead load deformation. The possible differences between the conventional and the proposed method are examined through numerical applications.     

Experimental visualization of microstructure evolution during suspension plasma spraying of thermal barrier coatings

This paper investigates the evolution of microstructure of thermal barrier coatings (TBCs) produced by suspension plasma spraying (SPS) through a careful experimental study. Understanding the influence of different suspension characteristics such as type of solvent, solid load content and median particle size on the ensuing TBC microstructure, as well as visualizing the early stages of coating build-up leading to formation of a columnar microstructure or otherwise, was of specific interest. Several SPS TBCs with different suspensions were deposited under identical conditions (same substrate, bond coat and plasma spray parameters). The experimental study clearly revealed the important role of suspension characteristics, namely surface tension, density and viscosity, on the final microstructure, with study of its progressive evolution providing invaluable insights. Variations in suspension properties manifest in the form of differences in droplet momentum and trajectory, which are found to be key determinants governing the resulting microstructure (e.g., lamellar/vertically cracked or columnar).     

MgO calcination for easy direct coagulation casting of aqueous alumina slurries

The reactivity of MgO with ammonium poly(acrylate) and diammonium hydrogen citrate dispersants was decreased by high-temperature calcination which enabled easy preparation of direct coagulation casting slurries without cooling. The decrease in reactivity of MgO with an increase of calcination temperature (30–1200?°C) was due to the decrease of surface area (52.7–0.7?m²/g) as a result of an increase of average particle size (285–2075?nm) as well as a change of particle morphology from flaky to near spherical. The MgO calcined at a temperature of 1000?°C and above provided sufficient time for mixing with aqueous alumina slurries by ball milling at room temperature (~30?°C) without producing an adverse increase in viscosity before casting. The setting time of 55?vol% alumina slurries was in the ranges of 260–1070 and 10–50?min at room temperature and at 70?°C, respectively, at MgO concentrations in the range of 0.1123–1.2?wt%. The faster setting at 70?°C was due to a combination of faster dispersant-MgO reaction, faster hydration of MgO and high valance counter ion effect.     

Removal of colloidal particles utilizing gelation reaction of sodium alginate

A novel technique utilizing the gelation reaction of natural polymers has been proposed for the separation of solid from liquid in difficult-to-filter colloidal suspensions. This technique is especially effective in the treatment of colloidal muddy water of high solid concentration, which is often produced as a byproduct of certain construction processes. Colloidal suspensions are mixed with a sodium alginate solution, and this mixture is added to a calcium chloride solution, resulting in the entrapping of colloidal particles by the calcium alginate gel. Gel suspensions are then drained gravitationally, followed by mechanical expression of gel particles. Fundamental aspects of this process are investigated by using sodium bentonite as an experimental material. The alginate-bentonite mixture is added dropwise to the calcium solution. Decreasing the droplet size of the mixture expedites gelation since the diffusion of calcium ions into droplets determines the rate of gelation reactions. Reducing the alginate content expedites expression of the gel since alginate content is inversely proportional to the rate of expression.     

物料性质、分离方法与操作条件的讨论——第二部分稀浓度润滑油两相分离方法的探讨

从过滤与分离基本原理出发 ,针对物料的特性以润滑油白土、悬浮液为例 ,确定过滤分离方法与操作条件。