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.     

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.     

Flow of slurries of coarse particles at high solids concentrations

Using a lock hopper feeding system, gravel and coal shale slurries containing particles of median diameter approximately 4 mm were transported at high concentrations through a pipe of I.D. 7.87 cm at velocities below 3.5 m/s^?1. In addition to the usual measurements of velocity, delivered concentration and hydraulic gradient, in-situ concentrations and particle velocities were determined. With these measurements, a two-layer model of stratified flow of the type proposed by Wilson was examined and found to give satisfactory predictions. Coefficients of wall friction were found to vary with velocity. Minimum values of these coefficients agreed with the results of direct shear tests. This variation could be attributed to stick-slip processes at low velocities and a change in the nature of the interparticle stress at higher velocities.     

Anomalous friction in slurry flows

Experiments conducted with water slurries of 1 mm particles of specific gravity 1.59 in a laboratory pipeline 0.105 m in diameter have provided evidence of a change in the friction mechanism at velocities above 3 m/s. These flows were stratified and at low velocities the frictional pressure gradients were in satisfactory agreement with the predictions of the conventional two‐layer model. However at higher velocities the friction is substantially lower than predicted. Measurements of concentration and velocity distributions within the pipe show that no major change in flow regime occurs concurrently with the change in the friction mechanism. It appears that the effect is due to a change in the nature of the particle‐wall interaction, of a type which suggests that an inward‐acting force affects the particles adjacent to the wall.     

The effect of particle shape on pipeline friction for newtonian slurries of fine particles

Experiments have been conducted to assess the effect of particle shape on pipeline friction in turbulent flow, using laboratory pipelines of nominal diameter 50 mm and 150 mm. The experiments were intended to examine the extent to which a fluid model is appropriate for slurries of this type, especially at high solids concentrations. The experiments confirm that fluid friction at low and moderate solids concentrations is proportional to slurry density, with particle shape being of minor importance. At high solids concentrations, additional increases in friction are observed and these depend upon the ratio of the solids concentration to the maximum settled concentration. Although this friction increase is qualitatively similar to that which would result from increased slurry viscosity, the evidence suggests that particle‐wall contact is the mechanism. However, the transition from turbulent to laminar flow indicates that an effective viscosity should be used in calculating critical Reynolds numbers.     

Experiments with concentrated slurries of particles with densities near that of the carrier fluid

Experimental investigations of headlosses and particle velocity distributions have been undertaken for water slurries of polystyrene particles of diameter d₅₀ = 0.3 and 1.4 mm. At concentrations greater than 40–45% by volume, nearly linear headloss vs. velocity relationships were obtained. These suggested laminar flow but the particle velocity measurements showed the flow to be turbulent. The results have been interpreted with an approximate theory based upon lubrication mechanics. The investigation illustrates the limitations of slurry viscometry in predicting pipeline behaviour for slurries of particles of this size.     

WALL SAMPLING FROM HORIZONTAL SLURRY PIPELINES

An experimental study of the errors associated with wall sampling from a horizontal slurry pipeline has been conducted. Experiments were performed for water-sand slurries flowing in a one inch horizontal pipeline. The effects of particle size (0.08 mm to 0.4 mm), upstream slurry solids concentration (4% to 12%, by volume), upstream bulk velocity (1.8 m/s to 4.0 m/s), sampler diameter (4 mm to 25.4 mm), sampler location, and sampling velocity ratio (defined as the ratio of the sampling velocity to the upstream bulk velocity, 0 to 4.5) on the sample solids concentration and sample particle size distribution were examined.

The experimental results show that the observed sample solids concentration and its particle size distribution are functions of the sampler location, sampler diameter and sampling velocity. For the case of sampling from the top or from the side of the pipe, the sampling efficiency (defined as the ratio of the sample solids concentration to the upstream solids concentration) was found to be always less than unity, and it increases as the sampling velocity increases. Also, the sample mean particle diameter is significantly smaller than that in the main pipe, especially at low sampling velocities. For sampling from the bottom of the pipe, the relation of the sampling efficiency to the sampling velocity ratio exhibits a maximum, and the sample mean particle diameter is very close to that in the main pipe.

The operating conditions upstream of the sampler also affect the sample solids concentration and its particle size distribution. The importance of the upstream bulk velocity, upstream solids concentration and particle size on the sample efficiency and sample particle size distribution depend on the sampler location.     

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.     

Computational method for coal slurry pipelines with heterogeneous size distribution

Design of industrial slurry pipelines is usually performed by applying semi-empirical procedures, requiring a significant experimental study for each project. This paper presents a new computational technique for coal slurry pipelines based on a two-phase flow analysis. The calculation model gives numerical solutions for the concentration, velocity and particle size distributions in the pipeline cross-section, which can be integrated to provide mean velocities and flowrates, delivered concentration, etc. Design calculations for headlosses can be performed using this approach for any set of given conditions: the properties of the transported material, carrier liquid and pipeline. The computational technique was developed using data for uniform sand—water mixtures flowing in pipelines of 51.5 mm, 263 mm and 495 mm diameter. The approach is extended to coal—water mixtures with heterogeneous size distribution of particles, and tested with experimental measurements in pipelines of 158 mm and 495 mm diameter. The model is shown to be a useful vehicle for generalizing experimental measurements and scale-up to headloss predictions.     

Bitumen effects on pipeline hydraulics during oil sand hydrotransport

Oil sand hydrotransport technology has become increasingly important to Syncrude Canada Ltd. and the oil sands industry. Oil sand slurries are complex, multiphase mixtures of bitumen, coarse solids, fine solids, water and air that can exhibit time‐dependent behaviour, wherein pipeline friction losses increase drastically with time. Four separate experimental programs were conducted to study the effect of bitumen on pipeline hydraulics using 100 mm and 250 mm (I.D.) recirculating and once‐through pipeline loops. The results show that pipeline friction losses increase as a bitumen coating forms on the pipe wall. The effect is more pronounced at 50°C, but also occurs at lower temperatures.     

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.     

Experimental investigation for near-wall lift of coarser particles in slurry pipeline using γ-ray densitometer

Experimental data are collected in 54.9 mm diameter horizontal pipe for concentration profiles using γ-ray densitometer. Two sizes of glass beads with mean diameter and geometric standard deviation of 440 μm and 1.2 and 125 μm and 1.15, respectively, are used. These data are collected for flow velocity up to 5 m/s and overall concentration up to 50% by volume for each velocity. Experimental data measured by sampling probe and pressure gradients in the previous study [D.R. Kaushal, K. Sato, T. Toyota, K. Funatsu, Y. Tomita, Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry, International Journal of Multiphase Flow, 31(7) (2005) 809-823.] are used to compare with γ-ray densitometer measurements and to study slip velocity and near-wall lift of particles in the pipeline. In overall, γ-ray densitometer and sampling probe give quite similar concentration profiles except for few cases of coarser (440 μm) particles at lower flow velocities. Measurements show that, for finer particles, point of maximum concentrations are near the pipe bottom (y/D = 0.1) and for coarser particles, maximum points are relatively away from the pipe bottom with decrease in shift as flow velocity increases. Pressure gradient profiles of equivalent fluid for finer particles are found to resemble with water data except for 50% concentration, however, more skewed pressure gradient profiles of equivalent fluid are found for coarser particles. Experimental results indicate absence of near-wall lift for finer particles due to submergence of particles in the lowest layer into the viscous sublayer and presence of considerable near-wall lift for coarser particles due to impact of viscous-turbulent interface on the bottom most layer of particles and increased particle-particle interactions. It is observed that near-wall lift decreases with increase in flow velocity; however, the effect of slip velocity on pressure drop is greater at lower flow velocities and less at higher flow velocities than near-wall lift of coarser particles in slurry pipeline. For finer particles, the departure from equivalent fluid pressure gradient profile at 50% concentration is attributed to the sudden increase of viscous sublayer thickness.     

Sensitivity analysis of the influence of slurry characteristics and pipe size on Wasp model's accuracy

Sensitivity analysis of Wasp model for pressure gradient in solid-liquid slurries was conducted. The experimental work was carried out in 22-mm ID and 45-mm ID pipelines utilizing slurries composed of spherical glass beads having particle size distribution (PSD) following the Rosin-Rammler distribution and mean size of 50 μm. The spreads of the distribution were 1.7 and 7, corresponding to wide and narrow distributions, respectively. The slurries examined in this study had concentrations ranging from 5% to 25% by volume. Statistical tests for equivalence of means and variances provided some evidence that Wasp model is more accurate in predicting pressure gradients for the slurries of narrower PSD and at higher solid concentrations. Although the model was designed specifically for relatively large pipes, it was found more accurate in predicting pressure gradients in the 22-mm ID pipeline than in the 45-mm pipeline. Experimental results obtained in the same flow loop diameter indicated that the slurry of the narrower distribution produced higher-pressure gradients than those for the slurry of wider distribution. Pressure gradient increased markedly with increasing slurry concentration regardless of the pipe diameter and slurry PSD. However, the pipe diameter was found to have more significant influence on the pressure gradient than the slurry concentration does.     

The effect of sand-clay slurries on the performance of centrifugal pumps

The addition of clay to sand slurries has been found to reduce the pipeline friction losses, thus lowering the pumping head and power consumption. Pump water heads and efficiencies are decreased by the presence of solid particles. Experimental results are presented for a centrifugal pump with an impeller diameter of 0.625 m for three narrowly graded sands with average particle sizes of 0.64, 1.27, and 2.2 mm. Reductions in head and efficiency of up to 30% were observed for sand slurries with volume concentrations of up to 35%. Head and efficiency were lowered by about one-third for sand-clay mixtures with sand to clay mass ratios between 4:1 and 6:1. Comparisons are made with design criteria and a mechanistic model approach based on a prediction of the relative motion of the solids and water in the volute region of the pump.     

The flow of “settling” slurries in tubes with internal spiral ribs

The secondary flows created by an internal spiral rib in an otherwise conventional smooth tube are illustrated by reference to the axial, and combined tangential and radial velocity components for a fluid flowing in a 2-inch diameter tube containing a rib with a pitch-to-diameter ratio of 3 The effect of such secondary flows on the transportability of “settling”(suspensions)was investigated by measuring pressure gradients for the flow of two sand/water slurries in a smooth 2-inch tube and in 2-inch diameter tubes with ribs of pitch-to-diameter ratio 5.15, 3.32 and 1.80. Average flow velocities ranged from 0.5 to 8 feet/sec. and delivered concentrations ranged from 5 to 18 per cent by volume While the ribs were found to be a disadvantage at relatively high average mixture velocities because of increased pressure gradients, they were found to be advantageous at relatively low velocities, i.e. velocities less than the critical deposit velocity for flow in the smooth tube, in that the pressure gradients, for a given sand/water slurry with a given delivered concentration and average velocity, were lower in the ribbed tubes than in the smooth tube. Because of this, the power consumption per unit mass of solid transported was reduced by the presence of a rib. The optimum pitch-to-diameter ratio was estimated to be about 5 Pressure gradients measured for one of the slurries with air added as a third phase showed the presence of air to be a definite disadvantage     

Flow of suspensions in pipelines(Part 2: Two Mechanisms of Particle Suspension)

The distribution of sand and nickel particles with height in a horizontal channel of rectangular cross section has been measured and eddy diffusivities have been computed from these measurements. Turbulent suspension of particles appeared to occur where the concentration of solid particles was low, the particle diameter was small (< 0.2 mm.) and the ratio of the settling velocity of the particles to the friction velocity of the flow was less than 0.2. Where these criteria were not satisfied, concentration profiles were observed to deviate significantly from the shape associated with turbulent suspension. These deviations are attributed to the effect of particle interactions investigated by Bagnold.     

Application of high-speed PIV and image processing to measuring particle velocity and concentration in a horizontal pneumatic conveying with dune model

The purpose of this study focuses on analyzing the particle velocity and concentration characteristics in a horizontal pneumatic conveying with dune model, so as to reveal the mechanism of the low conveying velocity and saving-energy conveying. The test pipeline consisted of a horizontal smooth acrylic tube with an inside diameter of 80 mm and a length of about 5 m. The polyethylene particles of density 978 kg/m³ and 952 kg/m³ with diameters of 2.3 and 3.3 mm are used as conveying materials. High-speed PIV was first applied to measure the time-averaged particle velocity and was proven to be an efficient measurement technique in the pneumatic conveying. Then the particle velocity and concentration distributions of three locations were measured at mean air velocities of 12 m/s and 13 m/s and the solid mass flow rates of 0.45 kg/s and 0.43 kg/s. A comparison of the particle velocity and concentration profiles between dune model and non-dune model was performed. It is found that the particle concentration of using dune model becomes higher in the upper part of pipeline and becomes lower near the bottom of pipeline in the acceleration region. The particle velocities of using dune model are clearly higher than that of the conventional pneumatic conveying along pipeline and display a uniform profile at the downstream. It is also clear that the particles can be effectively accelerated by increasing air velocity and impacting the surface of dune model. The effect of dune model on the velocity profile of relatively small particles is larger than that of the larger particles and maintains to the downstream.     

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.     

Failure and fragmentation of ceramic target with varying geometric configuration under ballistic impact

The failure and fragmentation of monolithic bare alumina 99.5% ceramic target and energy dissipation of steel 4340 projectile have been studied in a series of ballistic experiments carried out, with the incidence velocities in a range, 122–290 m/s. The velocity drop and energy dissipation increased with incidence velocity for 10 mm thick target with damage zone extended upon the whole area of rear face at higher velocities. The ballistic results obtained with the 10 mm thick target have been compared with the ballistic performance of the 5 mm thick target used in a previous study to explore the effects of target thickness on the failure mechanism. A model for the residual velocity of projectile after perforation of the single layered ceramic target has been developed based on the Lambert Jonas model by using the experimental data available for 5 mm and 10 mm thick alumina 99.5% target against 10.9 mm projectile. The residual velocities and damage patterns were reproduced with a reasonable amount of accuracy by a three-dimensional finite element model developed on commercial ABAQUS/CAE. The effect of obliquity and projectile diameter to target thickness ratio (D/T) on ballistic performance has been determined by the numerical simulation model with impact velocity in a range of 300–500 m/s. A spatial variation of ejected fragments velocity at different time steps was plotted to develop a velocity profile for the ceramic fragments coming out of the target. A semi-empirical model has been proposed for residual velocity after perforation of a monolithic ceramic target, relating to the incidence velocity and projectile diameter to target thickness ratio. The monolithic ceramic targets have been investigated for a comparative assessment of energy dissipation by the ceramic layer to eventually design an efficient front layer of a ceramic based composite armour in future studies.     

GAS-SOLIDS FLOW PATTERNS IN A CONCURRENT DOWNFLOW FAST FLUIDIZED BED(CDFFB)

Radial profiles of solid concentration and velocity for concurrent downward gas-solid suspension in a140mm inside diameter fast fluidized bed were investigated.The influence of gas velocity,solid circulating rateand axial position on radial profiles of solid concentration and particle velocity has been examined.It hasbeen found that an annular region of high solid concentration exists at r/R=0.94.At both the center and wallregion,the solid concentration and the particle velocities are relatively low.The shape of radial solid con-centration profile curves is mainly dependent on the cross-section averaged voidage,and the shape of radialparticle velocity profile is mainly affected by the gas velocity and cross-section averaged voidage.Based on the radial profiles of solid concentration and particle velocity,the solid mass flux profile and thenonuniformity of solids flow are discussed in this paper.It is shown that solids flow in CDFFB is much moreuniform than that in UFFB.