Settling velocities of particles in bubbly gas-liquid mixtures

The axial dispersion-sedimentation model is commonly used to describe the axial concentrations of solids in three phase bubble columns at low liquid velocities. When the two parameters of this model, the particle settling velocity and the solids axial dispersion coefficient, are uncoupled by the use of various assumptions, physically unrealistic values of these parameters often result. Direct experimental measurements of solids settling rates in bubbly gas-liquid mixtures were carried out. The measured mean settling velocities decreased slightly with gas flow rate and were equal to or slightly less than the single particle free settling velocity in the liquid alone. Solids axial dispersion coefficients were also obtained from the solids settling rate distribution data, and gave values considerably less than the experimental liquid axial dispersion coefficient.     

An improved two layer model for horizontal slurry pipeline flow

A model for predicting head losses for coarse-particle or settling slurries has been obtained. Experimental data for isothermal flows of sand, gravel and coarse coal slurries in pipes of industrial scale have been used to obtain the correlations in the model. The model differs from previous versions in the way it deals with the concentration of the lower layer and in the role ascribed to the finest (–74 μm) particles. The fraction of contact load, which contributes sliding friction at the pipe wall, is found to be primarily a function of the ratio of the mean flow velocity to the settling velocity of the mass median particle size in the (+74 μm) fraction. The correlations are restricted to mixtures containing less than 35% (+ 74 μm) particles by volume.     

Extending acoustic in-line pipe rheometry and friction factor modeling to low-Reynolds-number,non-Newtonian slurries

The rheology of non-Newtonian slurries is measured in a recirculating pipe loop using an acoustic velocimetry-pressure drop technique at very low flow rates and variable solids loadings. The technique avoids (a) settling at low solids concentration, a shortcoming of bench rheometry, by using a vertical test section, and (b) physical sampling, providing greater safety. Speed of sound in the suspensions is also modeled. In-line and off-line data are used to assess the suitability of several non-Newtonian models to describe observed flow behavior. Measured and predicted values of the friction factor are compared with the Madlener et al Herschel–Bulkley extended model found to be superior. The dependence of yield stress and viscosity on solids loading and particle size is investigated, showing complexities from aggregation on the particle size distribution require more interpretation than the choice of rheological or friction-factor model.     

惰性粒子流化床干燥钻井废泥浆实验研究

实验考察了惰性粒子流化床干燥钻井废泥浆,关联了干燥器的体积传热系数表达式,可定量计算进风速度、进风温度、废泥浆体积流量和含水量等参数的影响。结果表明,惰性粒子流化床干燥热效率达55％,体积传热系数可达6kW·m^-3·K^-1,可用于钻井现场柴油机废气干燥钻井废泥浆。激光粒度分析仪测试干燥产物粒度平均值为12／μm,且分布较为集中,其密度为3．2g·cm^-3,可以回用于钻井泥浆的加重材料。浸毒试验表明,干燥产物CODCr值大幅度下降。     

Stability of coal-water slurries made from ultrafinely divided coals of different metamorphic grades

The feasibility of mechanochemical preparation of coal-water slurries from coals of different metamorphic grades with the use of various chemical additives was examined. The effect of surfactants on the settling dynamics of particles in slurries at different particle sizes and different degrees of coal metamorphism was revealed as a result of the experiments.     

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.     

Determination of particle size distribution of salt crystals in aqueous slurries

A method for determining particle size distribution of water-soluble crystals in aqueous slurries is described. The salt slurries, containing sodium salts of predominantly nitrate, but also nitrite, sulfate, phosphate, aluminates, carbonate, and hydroxide, occur in radioactive, concentrated chemical waste from the reprocessing of nuclear fuel elements. The method involves separating the crystals from the aqueous phase, drying them, and then dispersing the crystals in a non-aqueous medium based on nitroethane. Ultrasonic treatment is important in dispersing the sample into its fundamental crystals. The dispersed crystals are sieved into appropriate size ranges for counting with a HIAC brand particle counter. A preponderance of very fine particles in a slurry was found to increase the difficulty of effecting complete dispersion of the crystals because of the tendency to retain traces of aqueous mother liquor. Traces of moisture produce agglomerates of crystals, the extent of agglomeration being dependent on the amount of moisture present. The procedure is applicable to particles within the 2 – 600 μm size range of the HIAC particle counter. The procedure provides an effective means for measuring particle size distribution of crystals in aqueous salt slurries even when most crystals are less than 10 μm in size.     

Effect of surfactants on the rheology of hematite slurries

The rheological behavior of aqueous hematite slurries has been studied by laboratory viscosity and flow measurements. Data are presented for slurries with volume concentrations of hematite up to 40%. Solids concentration and particle size distribution were found to be important variables in the rheological behavior of hematite slurries as contrasted to temperature which was found to have only a small effect. Chemical dispersant additives and viscosity control additives used in relatively small concentrations improved the flow characteristics of the hematite slurries. Specifically, a lignosulfonate dispersant markedly increased the flow of slurries containing finely divided hematite, −325 mesh, and a viscosity control additive increased the carrying capacity of other slurries for coarse particles.     

二氧化硅纳米颗粒对冰浆中冰晶粒径分布及存储演化特性的影响

分别以乙二醇水溶液和氯化钠水溶液为基液配制不同浓度的二氧化硅纳米流体并以此制备冰浆，通过显微装置获得冰晶图像，将实验得到的粒径分布与正态分布、对数正态分布、Gamma分布和Weibull分布进行对比，探讨纳米二氧化硅对冰晶平均粒径与分布特性的影响，同时观测储存过程中冰晶粒径演化规律。结果表明：加入纳米二氧化硅前后冰晶粒径分布均可用Gamma分布描述；纳米二氧化硅可起到细化晶粒的作用，而且添加浓度越高冰晶颗粒越小；当基液为乙二醇水溶液时，加入纳米二氧化硅可较好地抑制储存过程中的冰晶粒径增长，但基液为氯化钠水溶液时，纳米二氧化硅浓度需达到0.75%，才可抑制冰晶增大。研究结果证明，一定浓度的纳米二氧化硅流体可作为制冰溶液，起到减小冰晶粒径并控制冰晶生长的作用，这对冰浆流动和传热性能的改善具有重要的应用价值。     

Methods of improving settling of industrial pigment slurries

An experimental study on improvement of settling of three industrial pigment slurries, with trade names chrome yellow, molybdate orange and semi-blacktone iron blue is reported. Three methods for improvement were employed. Additions of common surfactants did not improve settling rate of any slurry. Additions of a flocculating agent with trade name Hercofloc 825.2, on the other hand, improved the settling rates of all three slurries very significantly. Settling of chrome yellow slurries was increased a phenomenally one hundred fold by additions of Hercofloc 825.2. The exposure of the slurries to low frequency (540 kHz and 765 kHz) ultrasonic radiation increased the settling rate as high as six to seven fold. The effects of ultrasonic radiation on the settling of iron blue slurry of various solids concentration, and initial slurry height were investigated. Exposure of the slurry to ultrasonic radiation appears to be a viable and practical method for improving settling of industrial pigment slurries.     

混床树脂分离效果预测的探讨

根据Ｓｔｏｃｋｓ模型,对混床用阳阴树脂沉降速度、沉降比进行计算和分析。结果表明,符合标准的阳、阴树脂沉降速度、沉降比有很大差别,粒度、密度不同,分离效果就不同,选择和评价混床树脂时,应对阳、阴树脂粒度分布、沉降速度、沉降比进行综合考察,以确定其分离效果。     

The Rheology of Peat/Solvent Slurries

Slurries of finely milled Irish peat in Shell White Spirit (100F) were prepared and their rheological behaviour was evaluated in terms of shear rate, solids concentration, moisture content and particle size distribution of the solids. The moisture content of the peat was found to be of crucial significance in determining both the effective solids concentration and the stability of the suspensions. The viscosity of slurries composed of 7% moisture peat solids were almost independent of solids concentration and displayed Newtonian rheological behaviour, with a viscosity of approximately 0·012 N s m⁻². The viscosity of the suspending medium was 1·006×10⁻³ N s m⁻² at 20±1°C. The viscosity of the slurries composed of 55% moisture peat solids was observed to rise sharply, up to about 0·10 N s m⁻² with solids concentration. The shear rate dependence of these suspensions was more complex and their flow characteristics were evaluated in terms of empirical non-Newtonian models. It proved difficult to confidently distinguish between the Bingham Plastic and Casson models as each gave best fit regression curves which were almost identical. Particle size distribution analysis of the suspensions indicates the formation of peat aggregates in the 55% moisture samples which exhibited more rapid settling of the solid. © 1997 SCI     

注凝成型微孔梯度陶瓷材料制备新工艺的研究(Ⅰ）

本文采用90年代初发明的注凝成型技术制备微孔梯度陶瓷材料。研究低粘度的Al2O3(不同粒度)和高温粘结剂混合物的浆料的制备方法;并以调整浆料的流变性为重点,研究了pH值、分散剂、固体含量、高温粘接剂、颗粒度对浆料粘度的影响。通过上述各种影响因素的工艺优化制备出了低粘度(0.364Pa*s)、高固体含量(体积分数为50%～54%)的Al2O3(W0.5,W1,W7和W10)浆料。     

Mineral Slurry On-Stream Particle Size Analysis

On-line particle size analysis of mineral slurries is important because of the potential impact of size distribution on downstream processs, such as filtration and slurry thickening. Matti Kongas, Outokumpu Technology, Finland, discusses existing on-line particle analysis technology and presents a new technique employing laser diffraction that is being successfully applied in the field.     

乳胶涂料中填料粒径测定与分散剂的选择

介绍了重力沉降法和容量沉降法两种测定乳胶涂料中填料粒径的方法。通过比较粉体粒径结果显示：沉降法比激光法更形象直观，更能代表体系粒径真实情况。以滑石粉、重钙、轻钙粉体为基准，采用不同用量、不同类型的分散剂的容量沉降法进行比较得出：用容量沉降法能定量地对分散剂性能做出评价。     

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.     

Preparation and rheology of biochar, lignite char and coal slurry fuels

Slurries of an Oil Mallee biomass char, a low rank coal char and sub-bituminous coals were prepared by mixing the finely milled solids with water and a range of additives including polyacrylic acid, charged copolymers D101 and D102, and sucrose. The resultant slurries were subjected to rheological characterizations including apparent viscosity and yield stress. The effect of the solid type, particle size distribution, and the additives on preparation of highly loaded slurries with the desired rheological behaviour were systematically examined in terms of apparent viscosity and yield stress. The additives D101 and D102 were found to be most effective in producing highly loaded suspensions with a low apparent viscosity and yield stress. Particle size distributions were manipulated to improve the solid loading. Suspensions produced by powder mixture containing equal weight precent of 30 min and 1 min milled powders gave a broad size distribution and is very effective in increasing the solid loading in slurries. The significant improvement in the solid loading was shown to be achieved by (i) increasing particle packing density via size distribution control and (ii) minimising the strength and number of the interactions between colloidal particles. The maximum solid loading of flowable (or relatively low apparent viscosity) slurries achieved with the Oil Mallee char is ∼40 wt.%, with the sub-bituminous coals 56-63 wt.%, and with the lignite char ∼65 wt.%. This study has shown that for low rank coals such as lignite, thermal and densification treatment is essential to achieve the solid loading of slurry fuel.     

Flow of slightly settling slurries in a horizontal rotary drum

An experimental study was conducted to examine the flow of slightly settling slurries in a horizontal rotary drum. The effects of the slurry flow rate, feed solids concentration, particle settling velocity and drum rotational speed on the hold-up solids concentration were investigated. At low drum speeds, the hold-up solids concentration was much higher than that of the feed. However, at higher drum speeds, the hold-up solids concentration approached that in the feed. At a given drum speed, the hold-up solids concentration was found to vary linearly with the feed solids concentration. A semi-empirical correlation was developed to predict the hold-up solids concentration using the drum Froude number, the single particle drag coefficient and a dimensionless slurry feed rate.     

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.     

RHEOLOGY OF VERY CONCENTRATED COAL SUSPENSIONS

Non-Newtonian viscosity curves of coal slurries were measured over a 3-5 decade shear rate range with a Weissenberg Rheogoniometer, for coal volume fractions up to 0.6 and particle sizes under 62 fim. Suspending media were Aroclor 1254 (a chlorinated biphenyl), glycerin, and glycerin with surfactant; these have densities very close to that of coal, so no settling occurred. Viscosity magnitudes generally exceeded predictions of correlations and theory established for spherical particles; explanations are sought in terms of particle aggregation, shape irregularity, and surface effects.