Showing papers in "Particulate Science and Technology in 1983"

An evaluation of the kuwabara model

Abstract: The Kuwabara model was developed to provide an approximate method of calculating the forces experienced by randomly distributed spheres or parallel circular cylinders in Stokes' flow. Although not specifically designed for the purpose, Kuwabara's model has frequently been used to describe the flow surrounding the individual fibers of a fibrous filter. In this paper an attempt is made to evaluate this application by comparing the Kuwabara flow field to that obtained by a numerical solution of Stokes' flow over an array of cylinders.

Optimal definition of class intervals for frequency tables

Abstract: Data sets are often analyzed in the form of collections of frequency tables (or percentiles derived from equivalent cumulative frequency distributions). Decisions concerning the number of intervals and interval width obviously affect the quality of the data in subsequent analysis. Relying on the basic concepts of information theory, a procedure is presented which evaluates the relative information content of a set of frequency data when subdivided in various manners. Maximum information is always preserved when “maximum entropy” histograms (with unequal class intervals) are used. Evaluation of several schemes of frequency table subdivision (phi-based arithmetic, log arithmetic, Z-score, log Z-score, maximum entropy) indicates that, surprisingly, collections of equal interval phi-based frequency tables contain the least information. Additionally, the concept of the relative entropy of a given collection of frequency tables is defined. The relative entropy is useful as a feature extractor wherein s...

The use of factor analysis in source determination of particulate emissions

Abstract: The development of multivariate statistical approaches to receptor models have focussed on factor analysis. Target transformation factor analysis (TTFA) offers the possibility of determining the number of sources and their elemental composition as well as their mass contributions. In this current work, a new approach is presented for calculating the mass contributions of each source to each sample. In addition an approach to estimating the uncertainties in the analysis is introduced. The method is applied to a subset of the Regional Air Pollution Study (RAPS) particulate composition data set for site 203 in July and August 1976. The data is divided into subsets covering the daylight (6 AM to 6 PM) or night (6 PM to 6 AM) samples. Similar source profiles are obtained for these subsets.

Floc size reduction in the turbulent environment

Abstract: The dynamic behavior of the particle size distribution (PSD) in wastewater treatment processes results from the interaction of a random growth process with nonlinear, stochastic hydrodynamics. Successful modeling of the PSD response to high dissipation conditions depends upon accurate quantification of the breakage mode, the local dissipation rate, transition probability, and the daughter particle size distribution; the inferential determination of these quantities from PSD data is difficult, at best. Direct photographic observation of floc breakup in a turbulent jet apparatus and in the Impeller stream of a baffled, agitated tank has provided opportunities to measure both the breakage mode and the daughter particle size distribution for individual parent floes. These data have been used in successful PSD modeling in lean, batch systems characterized by irreversible breakage.

A staggered array model of a fibrous filter with electrical enhancement

Abstract: A staggered array of parallel circular cylinders is proposed as a model for a fibrous filter. The flow field within the array is numerically solved utilizing Stokes' approximation. Electrical enhancement of the filter is modelled using the method of images. Predictions of pressure drop and collection efficiency are compared to experimental data and it is shown that while the model overpredicts the pressure drop it can give reasonable estimates of collection efficiency.

Tailings pond behavior and characterization of oil sand tailings sludge

Abstract: Oil sand tailings are disposed of in large tailings ponds by upstream dyke construction and beaching. Sand separates and forms a gentle beach; the thin sludge flows into the pond as a density current, sedimentation takes place, and the rate of density increase rapidly becomes dominated by consolidation processes. The effect of the presence of bitumen on particles is an acceleration of sedimentation as the result of plastic collisions and agglomeration of particles. However, consolidation time is lengthened because the sludge solids have low relative densities and permeabilities. New system definitions are presented to account for the presence of bitumen as a non-mobile phase. A nomogram for oil sand sludge is presented to allow direct determination of sludge density and solids content from bitumen and water content. New experimental procedures for index tests are given, as the presence of bitumen creates laboratory difficulties. Grain size analysis and clay mineralogy require removal of bitumen, ...

Scaling laws for particle breakup in nozzle generated shocks

Abstract: Conditions for the onset of particle breakup in normal shock waves have been investigated A normalized particle drag behind the shock has been determined in terms of gas stagnation conditions and particle diameter for a range of gas Mach numbers 1 ⩽ M1 ⩽ 5 by introducing appropriately defined particle Knudsen and Reynolds numbers into analytical expressions for the drag coefficient Numerical computations of the particle drag, normalized with gas stagnation pressure and particle area, indicate a peak at a gas Mach number M1 ≳ 22, The magnitude of the peak was found to decrease with increasing particle diameter and reservoir gas density Criteria for the onset of agglomerate breakup were defined in terms of a modified Weber number for the adhesion mechanisms due to Van der Waals forces, electrostatic attraction and adsorbed surface films These results indicate that larger more closely packed agglomerates made up of smaller constituent particles have a greater tendency to resist breakup for a gi

Friction losses for flow of slurries in pipeline bends, fittings, and valves

Abstract: Resistance coefficients for flow of suspensions of well defined glass beads of narrow size fractions in 1-inch and 2-inch straight pipes, in standard 45°, 90° and 180° bends, in 90° smooth bends of various curvature radii, and also in gate and globe valves were measured. The measurements were made for two sizes of fine glass beads, -325 mesh and -200-325 mesh, covering wide ranges of turbulent Reynolds number and solids concentrations from 0 to 50 weight percent. These friction loss data were analyzed with regard to the effects of Reynolds number and suspended solids concentration, and the calculated resistance coefficients were compared with those estimated from available design procedures recommended for turbulent single-phase Newtonian flow. Within the range of particle sizes examined in this work no particle size effects could be discerned. The effects of Reynolds number and suspended solids concentration on the friction loss measurement were calculated.

Morphological analysis, ten years of progress

Abstract: The need for and the principles of morphological analysis as applied to particulate matter are briefly discussed. Applications of morphological analysis to a number of problems are cited. Topics include: relating morphology to the mechanisms of powder production; wear debris analysis by morphological analysis; and kinetic modeling of crystallization processes. Relationships between the behavior of particulate materials and the morphology of the particles are discussed in connection with: abrasive wear of metals; sedimentation In low flow regimes; measuring of bulk properties including internal angle of friction and flow times; dry separation technology; and scrap recovery techniques. The adaptation of the particle image analyzing system to analyze color as a morphic feature is presented. A number of examples of mixture analysis - classification studies are detailed and finally future work in packed and fluidized beds and slurry transportation is outlined.

Particle morphology applied to characterizing abrasive materials

Abstract: This paper reports the first quantitative relationship between hape and abrasive wear rate of steel.

PHASE AND MORPHOLOGY OF PbNb2O6 OBTAINED BY MOLTEN SALT SYNTHESIS

Abstract: : The morphological development of lead metaniobate powder particles in KCl is examined with special emphases on the heating conditions and starting compositions. Potassium ions are substituted in the Pb-site resulting in Pb;-xK2Nb2O6(PKN) with the orthorhombic modification. The morophology particles changed during PKN formation and particle growth. During the formation process of PKN, equiaxed and rod-shaped particles were obtained both above and below the melting temperature of KCl. The rod-shaped particles have a columnar structure but decrease in number with increasing potassium content in the starting mixtures. During the growth process, equiaxed particles grew to simple rod-shaped particles without a coulmnar structure. Potassium in the starting oxide was found to promote the formation of simple rod-shaped particles is obtainable. Originator-supplied keywords include: Molden Salt Synthesis, Lead Niobates, Potassium Chloride, Ceramics.

Wet classification and wet screening of fine particles

Abstract: (1983). WET CLASSIFICATION AND WET SCREENING OF FINE PARTICLES. Particulate Science and Technology: Vol. 1, No. 4, pp. 393-408.

Effects of grinding aids vibration milling of aluminum

Abstract: Fine aluminum powder is widely used in making paints, printing inks, slurry explosives, pyrotechnic chemicals etc. Hence the production of aluminum powder is highly important. In this paper the effect of grinding aids on the grinding characteristics of aluminum in a vibration mill under an inert atmosphere of nitrogen has been investigated. It is found that the use of grinding aids is essential in grinding of atomized aluminum. Among four different grinding aids, stearic acid appears to be the best grinding aid.

Design and calibration of a stack sampler for oil fly ash

Abstract: A particle sampling system was developed for the collection of Fly ash the stacks of ail-fired electrical generation plants. The apparatus has a cyclone separator which is designed to provide a cutpoint of approximately 2.5 µ followed by a pulse jet fabric filter. Flow rate is a nominal 226 L/min (8 cfm). The system was tested in the laboratory with monodisperse aerosols to determine the fractionation characteristics of the cyclone and the inlet probe. Efficiencies of three candidate filters were examined with clean media, with a dust cake and with the dust cake removed. Tests were conducted using monodisperse polystyrene aerosols of 0.50, 0.76 and 1.09 µ The pulse Jet apparatus was checked by operating the system at a flow rate of 200 L/min, loading the filter with AC fine test dust, and determining the stable filter pressure drop as a function of pulse jet air pressure.

Removal of fine particles from nonaqueous media by cross-flow electrofiltration-hydrodynamics and mass transfer

Abstract: An improved method of removal of fine particles suspended in nonaqueous media by the application of a high-voltage electric field was previous developed. However, to better understand the cross-flow electrofliter for future design improvements, a mathematical analysis of the filter was performed and more experiments were conducted with filter tubes of several porositites. Experiments were conducted with α-Al203, particles suspended in tetralin. Outlet concentrations of the concentrated slurry were measured with a gamma ray densitometer. A description of the flow field in the cross-flow electrofilter was obtained by solving the Navier-Stokes equations for annular flow with suction through an outer porous wall. A perturbation solution for the flow field was then used in a mathematical model which describes the concentration distribution in the electro filter. Numerical solutions were obtained by using the Crank-Nicholson finite difference method. Clear boundary layers near the filter wall were calc...

Particle morphology and bulk properties

Abstract: Experimental results relating bulk properties to newly developed shape terms are presented in this paper. The properties studied are tap density, apparent density, processing parameter, flow time, and angle of internal friction of several materials. The correlations obtained demonstrate the utility and the potential of morphological analysis.

Contact number as an index of transverse mixing in a motionless mixer

Abstract: A geometrical and microscopic mixing index defined by the contact number was used to study the transverse mixing in a Kenics motionless mixer. The mixing index, a measure of transverse mixing, increased exponentially as the number of helices in the motionless mixer increased. The helices in the mixer also had the significant effect of reducing the void fraction of the mixture. The relationship between the coordination number and the compaction in the mixture through the mixer was studied. The mean coordination number indicates that the packing of these mixtures are between the cubic and hexagonal packings.

The agglomeration and aging of terephthalic acid particles in liquid solution

Abstract: (1983). THE AGGLOMERATION AND AGING OF TEREPHTHALIC ACID PARTICLES IN LIQUID SOLUTION. Particulate Science and Technology: Vol. 1, No. 4, pp. 409-417.

High concentration dust mass monitor

Abstract: The development and testing of a portable, rugged, self-contained monitoring prototype instrument capable of detecting and measuring airborne, potentially explosive, dust levels at concentrations in the range of 20 to 500 g/m3, has been completed. The output signal provided by this monitor is designed to be essentially independent of particle size and composition. Direct mass concentration readout as well as internal memory capabilities for unattended operation have been incorporated in this device. The design emphasizes rugged-ness, versatility of operation, and adherence to intrinsic safety requirements. The sensing method incorporated in this monitoring instrument is based on direct air-path beta attenuation detection across a gap of the order of 2 centimeters using a very low energy beta-emitting isotope (Ni-63). The measurement system includes automatic periodic clean-air referencing in order to compensate for any air density fluctuations and/or detector drifts. Measurements, directly indica...

Measurements and analysis of the particulate emission from a direct injection diesel

Abstract: For five different operating conditions of varying speed and load, measurements have been made of the particulate emissions using a mini-dilution tunnel operated at different dilution ratios and air temperatures. Particles were sized by electron microscopy and employment of interactive computer graphics. Analysis of the results led to conclusions that the organic fraction of the particulate can be explained by either an adsorption or condensation interaction with the gas phase. In modeling these processes one has to account for the multi-component nature of the organic species and that adsorption is multilayer. 21 references, 14 figures, 3 tables.

Problems encountered in accurate determination of interparticle forces in ordered mixes

Abstract: The resistance of ordered mixtures to component segregation during processing is dependent upon the adhesion forces between the fine adherent particles and the carrier component within ordered units. A method is described that allows the adhesion force acting on individual adherent particles to be determined, using ultracentrifugation to apply a wide range of separating forces. Individual ordered units are located at the end of fine holes drilled through a thin brass plate and fixed in position with transparent adhesive tape.The plate is mounted in a specially constructed holder during ultracentrifugation, the axis of the holes being parallel to the centripetal acceleration, photomierographs, using a modified microscope with an enhanced depth of field of view, of the distribution of adherent fines were made after each period of ultracentrifugation. Comparison of photomicrographs enabled the determination of the numbers of fine adherent particles dislodged after each period of ultracentrifugation....

Morphic characteristics of grain dust

Abstract: The theory of morphological analysis is explained. The equipment and procedures used are presented. The technique is applied to electron micrographs of cyclone tailings corn and wheat dusts. Some preliminary results are indicated.

Cluster theory for the concentration dependent translational self-friction coefficient of rod-like macromolecules in suspensions

Abstract: A general theory of the concentration dependence of the self-friction coefficient of rod-like macromoiecules is presented based on multiple scattering ideas.Using the Riseman-Kirkweed model for Dolvmer, exdHEit farmyls are derived by taking both the hydrodynamic and the direct potential interactions between the solute molecules into account. Ana1vtical resullts are obdantned For the leading concentration dependence of the translational self-friction coefficient under theta conditions.

A procedure for correcting measured particle size distributions for undetected fine particles

Abstract: A simple procedure is described which can be used to correct size distributions obtained fron measuring devices which do not detect particles smaller than some limiting size. The method involves fitting the measured distribution to the Gaudin-Schuhmann Law but involves no assumptions regarding the size distribution outside of the measurement range. Application of the procedure is illustrated using simulated size data.

Characterization of the behavior of composite particles in a lead-zinc flotation circuit

Abstract: The computerized scanning electron microscope system (QEM*SEM) as developed for characterizing whole mineral particles by the CSIRO Division of Mineral Chemistry, Institute of Energy and Earth Resources, has proved to be a very useful tool in the analysis of products and intermediate samples in the Lead-Zinc Concentrator of Mount Isa Mines Limited. Two examples of the application of the method are given in the present paper. The analysis of final cleaner concentrates from two distinct ore blends has indicated that in each case most of the galena in the 10–37μm size range is fully or nearly fully liberated. This proportion decreased down the third cleaner cell bank. Coarser particles, in the 37–53μm size range, were shown to have smaller proportions of galena in the highly liberated galena classes. The remainder of the galena in each case is spread over the lower galena classes, which become increasingly interlocked with gangue. Significant proportions of gangue, both sulphide and non-sulphide were also found to be free or almost free from interlocking with galena, especially in the 10–37μm size fraction. Thus lack of selectivity, as well as composite particle flotation, is seen to be responsible for downgrading of lead third cleaner concentrates. In addition, the QEM*SEM technique has shown that the distribution of galena intergrowth in lead first cleaner tailings is spread over most composite classes, more akin to regrind/retreat particles than to lead primary rougher tail particles. Thus QEM*SEM provides a valuable method in the mineral industry of today of measuring the relative degree of liberation of ground ore or flotation products, and the extent of dilution of concentrates by non-selective flotation of liberated gangue. Full liberation is not always desirable because of the cost of grinding to the finest sizes and because non-selective dilution of concentrates by fine liberated gangue often increases. QEM*SEM can also play a useful role in deciding the best destination for intermediate concentrator streams.

Non-parabolic filtration behavior

Abstract: In this paper, the multiphase equations of change are used as a theoretical hasis for analyzing constant pressure, non-parabolic filtration behavior. This theory, verified by experiment, predicts that the medium resistance is the dominant factor influencing filtrate rates and that septum selection, relative to the particulate phase, is the key variable affecting non-parabolic behavior. Experimental data also shows that non-parabolic behavior is more energy efficient than parabolic and that non-parabolic behavior cannot be attributed to non-Darcian effects.

Application of liapunov's second method of stability to gas-solid transport

Abstract: Liapunov's second method of stability was applied to two basic equations describing particle and gas velocities during horizontal gas-solid transport. System parameters were then varied to determine which, if any, had a significant effect on the conditions at which the transport system borders between stability and Instability. The regions of asymptotic stability (RAS) increase with an increase in particle diameter, particle density and linear pressure drop but decreases with an increase in fluid density. The line diameter is not a significant parameter for changing the RAS. Actual experimental data must be tested to evaluate the usefulness of the analysis.

Particle shape and hyorocyclone efficiency

Abstract: Particles that are size classified in a hydrocyclone experience a complex force environment which includes forces proportional to size, shape, and specific gravity Inefficient size classification occurs if particles of the same size and specific gravity appear both in the overflow and underflow streams Fourier shape discriptors were used to show that the variation of drag forces due to particle shape was a significant factor in this inefficiency, thus providing a tool for better hydrocyclone design

Shape characterization of two-dimensional forms by a fraction of ellipse and diamond

Abstract: Meloy's method is extended in its use to characterize two dimensional forms by a fraction of ellipse and diamond. The Fourier coefficients are calculated for a vectorial expression of the form about the center of gravity. The value interpolated at the wave number 10 is a good measure for the macroscopic shape, which is assumed to be expressed as a fraction of the values for elippse and diamond. As the microscopic shape index the surface roughness of the form is discussed in terms of the perimeter divided by that of the equivalent ellipse which has the same area as the particle. The shape analysis is applied for various particles of the reference standard dusts.

A numerical model for steady nonpoint source dispersion of wind-blown fine particles from storage piles and experimental study

Abstract: This study is concerned with modeling of the loss of fine dust from storage piles and their dispersion in the atmosphere. The results of downwind particulate dispersion are tested by means of a two-dimensional wind tunnel model using tracer particles. The study shows that a wind barrier located two to three pile heights upstream will effectively reduce the wind blowing of fine particles from storage piles and the downwind particle density. The tracers used in the experiment are smoke, magnesia, latex, and glass particles. The particle sizes studied range from 15 μm to 75 μm. Experimental results indicate that the effects of particle settling due to gravity force will be negligible when the particle settling velocity is less than 0.03 m/s. If particle size is less than 15 μm, particles will most likely remain in a suspension state over a long distance. Finite difference techniques are used for steady state numerical simulation of particulate dispersion. The effects of the particle sizes, wind velo...