Deposition velocity correlation for water slurries

a Correlation to predict the deposition velocity of aqueous slurries is presented. The correlation employs the viscosity and density of the mixture of fluid and (-74 μm) particles, as well as the mass median diameter (d₅₀) of the fraction coarser than 74 μm. The correlation is derived from isothermal flow experiments using pipelines of diameter between 0.053 and 0.495 m.     

Modelling high concentration settling slurry flows

The well‐known two‐layer model for predicting friction losses for pipeline flows of settling slurries has been extended to solids concentrations above 35% by volume. This has been achieved by incorporating new experimental results to account for increases in friction which have been observed with “settling” slurries at high concentrations. The kinetic (fluid‐like) friction appears to increase with solids concentration in a manner which suggests that particle‐wall contact plays an important role. The experiments also suggest that the fraction of the total solids which contributes Coulombic (velocity insensitive) friction also increases to some extent at high concentrations. This effect is expressed in a tentative correlation which employs a slurry Reynolds number. In addition, new experimental measurements of delivered and in‐situ concentrations have been used to test predictions made with the previous version of the model. The measurements show that the interracial friction factor proposed recently by Wilson and coworkers is preferable for slurries of coarse particles.     

Hydrotransport of solids in horizontal pipes: Effects of solids concentration and particle size on the deposit velocity

Correlations previously proposed in the literature for the deposit velocity in the flow of settling slurries in horizontal tubes generally predict increasing values with increasing solids concentration. However, the present comprehensive investigation which has drawn on data from a broad geographical base, confirms that the deposit velocity shows a maximum with respect to concentration and decreases above about 15% by volume solids. It is also shown that the presence of fine particles (<75 μm) is particularly significant in determining the degree of the reduction in the deposit velocity for the higher concentrations. This reduction would appear to be due primarily to a significant increase in the drag coefficient for particles settling in a fine particle suspension, i.e. heavy medium. The data are summarized in graphs for a variety of materials including sand, gravel, iron ore and coal.     

Empirical correlations for the minimum transport velocity of multidisperse slurries in horizontal pipes

Empirical methods were developed for the prediction of minimum transport velocity (MTV) of settling slurries through horizontal pipes. Multidisperse slurries of different particle sizes and densities were included in the development of correlation. The correlation is based on the separation of the general particle volume dependence and the limiting MTV at zero volume fraction. The latter was calculated assuming a monodisperse slurry of the least readily transportable group of particles in a hypothetical fluid. For pipe diameter less than 50 mm and total volume fraction of solid less than 0.15 the prediction showed satisfactory agreements with experimental values.     

Deposition velocities for newtonian slurries in turbulent flow

In this contribution both new and previously published deposition velocity data for aqueous Newtonian slurries are incorporated in a correlation which complements the earlier predictions of Durand, Wilson and A.D. Thomas. Most of the new data has been obtained for slurries of narrowly sized sand particles of median diameter ranging between 90 and 420 μm, in pipes of diameter between 0.05 and 0.5 m. The data were obtained in laboratory investigations under isothermal flow conditions.     

Performance of Sand Slurry Pipelines in the Oil Sands Industry

Operating data for several slurry pipelines in the Alberta oil sand industry have been sampled and interpreted with the assistance of the Saskatchewan Research Council (SRC) Two‐Layer model. The slurries are described within the industry as normal tailings, dense tailings, or oil sand slurries. All are of the so‐called heterogeneous or settling slurry type. The pipelines considered ranged in diameter between 0.483 m and 0.737 m. The useful operating data included water and slurry pressure drop measurements recorded during periods in which velocities and densities were nearly constant. The data reveal that the friction is often higher than predicted by the SRC Two‐Layer model, which makes no allowance for the effect of large particles (>50 mm) which are known to be present. This friction increment appears to be higher when the pipelines have sections with upward slopes.     

A Rational Basis for National Ambient Air Standards for Particulate Matter

The aspiration of large particles (18–30.5 μm) in the human nose was studied to determine the inhalation efficiency as a function of particle size, and to evaluate the upper size cutoff for inhalable particles in still air. Under these conditions, the ability of a particle to be inhaled is dependent on the inhalation velocity entering the nose and the particle terminal settling velocity. Nasal inhalation of radiolabeled pollen and wood dust aerosols was measured in four subjects at normal resting breathing rates. The efficiency of nasal aspiration was found to decrease as the square of the particle size. The upper size cutoff for inhalability was estimated to be approximately 39 μm in still air.     

Combustion of Boron-Based Slurries in a Ramburner

In a combustion chamber equipped with windows, boron and boron alloy slurries were burnt. The fraction of the solids in these mixtures was 25%. For the quantitive analysis of the reaction products, three spectrometer systems were used: an optical multichannel analyzer for the range 0.2 μm to 0.9 μm, an acusto-optical tunable IR-filter for the range 1.2 μm - 2.4 μm, and rotating IR-filters covering the range from 2.5 μm to 14.5 μm. The determination of the gas-phase temperature of the exhaust plume was obtained by evaluation of the OH rotation bands. The particle temperature was measured with a fast two-color pyrometer. During the burning process of boron with an average particle size of 2 μm, only a weak background radiation was detected. Mg and AlB₂, produced a greater amount of particles in the exhaust due to their particle size of about 50 μm. The spectra of the exhaust plume show typical bands for the particular metals and the combustion products of the JET Al fuel. Particle size distribution, surface characteristics, and temperature are important parameters for the ignition and combustion of solids. Also, the flow field inside the combustion chamber influences the burning behaviour of the solid particles. Therefore the slurries were injected against the main flow direction to produce high turbulence.     

用毛细管粘度计测定易沉降固液悬浮体的粘度

测定固液悬浮体粘度时,流体进入毛细管前应有良好的搅拌,但它将引起入口端额外的端效应.本文引入了一个惯性校正项,可以有效地解决搅拌下毛细管粘度计的标定及固液悬浮体粘度的测量问题.根据上述标定结果用毛细管粘度计对氨性溶液与镍红土矿配成的矿浆进行了粘度测定.实验表明,固体粒子体积浓度较低时,该流体近似牛顿流体,其粘度与体积浓度的关系可用Vand方程式表示,即μ/μ_0=exp(bc_V).     

A pipeline transport correlation for slurries with small but dense particles

Most correlations/models for minimum transport or critical velocity of slurry were developed for slurries composed of particles greater than ～100–200 µm diameter with narrow particle‐size distributions which is typical of the minerals industry. Many other process industries handle smaller particles. In particular waste slurries at the U.S. Department of Energy's Hanford Site have broad size distributions and significant fractions of smaller particles. Despite the size of these wastes, recent studies at Pacific Northwest National Laboratory indicate that the small particles might be of sufficient density to pose a significant risk for pipeline deposition and plugging. To allow predictive assessment of deposition of fine dense particles for waste slurry transport at the U.S. DOE Hanford site, a pipeline‐transport correlation for critical velocity was developed using a simple power‐law between two dimensionless numbers important for slurry transport, the deposition Froude and Archimedes numbers. The correlation accords well with experimental data for slurries with Archimedes numbers <80 and is an adequate pipeline design guide for processing Hanford waste slurry.     

Particle Suspension in a Rotating Drum Chamber When the Influence of Gravity and Rotation are Both Significant

In recent years, rotating chambers have been found to be an effective method of retaining particles suspended in the air for an extended period of time. Rotating drum chambers have the potential of providing a stable atmosphere of well-characterized inhalable particles for periods lasting from hours to days for use in inhalation toxicology studies. To aid in planning for the use of rotating drum chambers in inhalation studies, we created a model that describes (a) the concentration of particles in the chamber under various conditions and (b) the particle sizes for which gravity and rotation influence particle dynamics. Previous publications describe the suspension / deposition of particles when the rotational effect is dominant, but do not describe particle suspension / deposition when gravitational settling is significant as occurs when such drum chambers are operated at optimal conditions for retaining the highest fraction of particles over time. By using the limiting trajectory of particles, the fraction of particles that remain suspended in a 1-m diameter rotating drum chamber was derived for forces of gravity only, rotation only, and gravity plus rotation. For particles between 0.5 and 1 μm in diameter and for suspension times of < 96 h, there was no loss of the suspended particles for drum rotation rates from 0.1 to 10 rpm. For 2- and 5-μm diameter particles, > 98% and 91%, respectively, remain suspended after 96 h under optimal rotation of the drum chamber. Optimal rotation rates were independent of particle size for particles < 10 μm in diameter (agreeing with Gruel et al. [1987] even though we predicted suspended fractions higher by > 30% for 10-μm particles after 96 h). For 20-μm diameter particles and suspension times < 96 h, the maximum suspended fraction occurred for drum rotation rates between 0.3 and 0.5 rpm. The particles > 2 μm can be selectively removed from an airborne particle size distribution in time periods of < 15 h when the rotational rate is > 5 rpm.     

Theory of Clarifier Operation. I. Quiescent-Hindered Settling of Flocculating Slurries

Abstract

The operation of quiescent (batch) clarifiers operating in the Class III mode (hindered settling) with flocculating slurries is modeled by means of a set of nonlinear partial differential equations, the continuity equations for the individual species of particles. Disintegration of the larger particles by viscous drag forces is assumed to be first-order. The equations are integrated numerically for the case of batch settling (such as is used in jar tests), and the dependence of settling characteristics on the parameters of the model is studied.     

The entry length for slurries in horizontal pipeline flow

The entry length for horizontal slurry pipeline flows has been determined experimentally using a pipeline of diameter 50 mm. Concentration and velocity distributions have been measured in the vertical direction at positions 6, 50 and 185 diameters downstream of the entrance. The measurements show that the entry length is of the order of 50 pipe diameters for sand slurries. High particle settling velocities give somewhat shorter lengths than intermediate settling velocities. With lower density polystyrene particles for which dispersive effects are important, the entry length is significantly greater than 50 diameters. The velocity distributions show that the velocity profiles develop concurrently with the concentration profiles. For sand slurries, a two-dimensional simulation gives a satisfactory representation of the developing concentration profiles.     

Experimental Study of Particle Deposition on Semiconductor Wafers

A sensitive method for detecting particle deposition on semiconductor wafers has been developed. The method consisted of generating a monodisperse fluorescent aerosol, depositing the known-size monodisperse aerosol on a wafer in a laminar flow chamber, and analyzing the deposited particles using a fluorometric technique. For aerosol particles in the size range of 0.1–1.0 μm, the mobility classification-inertial impaction technique developed by Romay-Novas and Pui (1988) was used to generate the monodisperse test aerosols. Above a particle diameter of 1.0 μm, monodisperse uranine-tagged oleic acid aerosols were generated by a vibrating-orifice generator. The test wafer was a 3.8-cm diameter silicon wafer placed horizontally in a vertical laminar flow chamber which was maintained at a free stream velocity of 20 cm/s. A condensation nucleus counter and an optical particle counter were used to obtain the particle concentration profile in the test cross section and to monitor the stability of aerosol concentration during the experiment. The results show that the measured particle deposition velocities on the wafers agree well with the theory of Liu and Ahn (1987) in the particle size range between 0.15 and 8.0 μm. The deposition velocity shows a minimum around 0.25 μm in particle diameter and increases with both smaller and larger particle size owing to diffusional deposition and gravitational settling, respectively.     

磷矿颗粒流态化特性的实验研究

在高1 m、内径42mm的流化床中,对粒径54-600 μm、密度2 252-2 665 kg/m3的磷矿颗粒的流态化特性进行实验研究.实验结果表明:磷矿颗粒粒径和密度对磷矿颗粒流态化行为有较大影响,床层膨胀比随着磷矿颗粒粒径的增大而逐渐减小.当磷矿颗粒属于Geldart B类颗粒时,流化较好;而当颗粒平均粒径为82 ...     

Settling stability of coal slurries prepared by wet grinding in the szego mill

Static sedimentation experiments on coal-#2 oil and coal-water slurries, wet ground in a Szego mill, were conducted. These slurries contain more flaky particles as compared to those conventionally ground. Concentration and size distribution of the coal, diameter and height of the settling columns and settling time were the independent variables. Coal concentration and particle size distribution along the columns, and settling rates were measured. Despite their particle shape differences, these slurries were similar to others in terms of settling stability due to particle flocculation.     

双组分大差异颗粒在气固流化床内混合/分离特性

实验考察了FCC催化剂(d_p=90 μm)和分子筛(d_p=1875 μm)构成的双组分大差异颗粒体系在流化床内的混合/分离特性。结果表明,在密相床层,随着大颗粒初始比例X₀逐渐增加,床层稀密相界面处的单位高度压降逐渐上升。双组分混合颗粒完全流化时密相床层内大颗粒质量分数在径向上总体分布均匀,但随着表观气速的增加大颗粒在径向上呈现出边壁高中心低的“U”形分布。全床混合均匀性在X₀<20.0%时较佳,且均匀性会随着表观气速u_g增加和X₀的增加而逐渐减小。在稀相空间,被夹带到稀相空间的大颗粒随着表观气速u_g增加逐渐增大,随着X₀的增大先增大后减小,当X₀=68.5%时夹带量最大。稀相空间内大颗粒质量分数在径向上呈“M”形分布,并且随着轴向高度的增加逐渐由“M”形分布转变为倒“U”形分布。基于实验结果,给出了计算完全混合高度和分级效率的经验关联式。     

Effect of coal particle size distribution,volume fraction and rank on the rheology of coal–water slurries

The aim of this study was to understanding of the effect of coal particle size distributions on rheology of coal–water slurries (CWS). Experiments have been carried out on the coal samples that were different in rank. Besides two different Turkish lignites (Soma and Istanbul–Agacli), a bituminous coal from Siberia (Russia) has been used. In addition to the determination of the chemical and physical properties of the coal samples, their zeta potentials were also measured. The pulps of different solids percentage composed of coal particles with d₅₀ sizes of 19, 35 and 50 μm were used to determine the effect of volume fraction on the viscosity of the slurry.     

循环流化床中C类颗粒的干燥

为将循环流化床(CFB)技术应用于C类颗粒(＜30μm)的干燥,在自建的循环流化床(内径0.104 m×高2.35 m)内,以玉米淀粉(dp=8 μm,ρp=800 kg/m3)为研究对象,考察了不同操作参数对其干燥特性及干湿分离情况的影响.结果表明:循环流化床适用于C类颗粒的干燥;干燥速率随气速及进风温度的增大而增大...     

新型溢流器高效回收钛白酸解尾渣中的钛

中国是世界上最大的硫酸法钛白生产国,目前已累计堆积超过千万吨副产品酸解尾渣。酸解尾渣中含有大量未反应的粒径大于25 μm的钛铁精矿,酸解尾渣堆积而不利用就造成了严重的环境污染和资源浪费。根据酸解尾渣颗粒沉降实验分析,发现酸解尾渣料浆具有良好的沉降和易分层特性。通过建立干扰沉降末速度计算式,得出酸解尾渣中颗粒切割粒度25 μm的沉降速度为0.60 mm·s^-1。基于流动、分选机理和沉降特性分析,设计了适用于酸解尾渣分离工艺的新型DTB（draft tube babbled）溢流分离器,并进行了结构参数优化,获得了溢流器最优结构参数和最佳分离效果。结果表明,外排溢流含有极少量大于25 μm的钛铁精矿颗粒,回收的钛品位达27%,回收率为73%。这些结果为大规模回收酸解尾渣中钛资源提供了基础数据。