bluuebunny/crossref_metadata_2025 huggingface dataset:
Feature‐specific Measurement of Surface Roughness in SEM Images
Authors: Russ John C. , Russ J. Christian
Published: December 2004

Characterization of the roughness of surfaces of individual features present in SEM images is obtained from the slope and intercept of a plot of the brightness difference between pixels as a function of their separation distance, in directions parallel and perpendicular to the scan lines within the outlines of the feature. The descriptive names contrast and texture are given to the intercept and slope of this plot, respectively. These parameters can be used to classify features, just as measures of size, shape, etc. are used for selection, distribution plots and statistical comparison. Evidence is also shown for a correlation between the texture and the fractal dimension of the feature profile, and consequently with the surface fractal dimension of the feature.
Alternative Model‐Independent Inversion Programme for Malvern Particle Sizer
Authors: Bayvel Leopold P. , Knight Jonathan , Robertson Gerald
Published: December 2004

The Malvern Particle Sizer, developed in 1977, is used extensively for measuring the size distribution of solid particles and drops. It has several modes of operation based on a priori assumption of a particle size distribution function and a so‐called “model independent” programme in which no prior assumptions are made about the nature of the size distribution. Unfortunately neither the developers nor the manufacturers of the instrument have revealed the algorithm which is used to obtain the particle size distribution from the light scattering data. A number of people who have attempted to verify the performance of the instrument using the model‐independent programme have encountered discrepancies which cannot be explained without knowing the details of the Malvern inversion algorithm.

The results obtained in this paper show that the light scattering data recorded, using the hardware of the Malvern instrument, can be successfully processed using Shifrin's inversion technique in order to the obtain particle size distribution. The use of Shifrin's inversion algorithm, which is described fully in the open literature, has a number of advantages over Malvern's proprietary software in the context of particle sizing research. It provides the research worker with a simple and mathematically elegant alternative method of processing the light scattering data which is particularly suitable for investigating the limits of applicability of the Fraunhofer diffraction particle‐sizing technique.
Comparison of Methods for the Measurement of Linear Grade Distributions in Liberation Analysis
Authors: Lin Chen L. , Miller Jan D. , Herbst John A. , Rajamani Kuppuswamy
Published: December 2004

An evaluation was made to assess whether linear grade distribution measurements determined from polished sections of randomly oriented particles can be used to estimate the extent of liberation for multiphase particles of specified size. Two techniques, optical image analysis and microprobe analysis, were used to establish the linear grade distributions for samples of different composition from a copper porphyry flotation circuit and these two were found to be equivalent. An estimate of the variance in the experimental data was made by measuring the average chalcopyrite content in these samples and comparing the results to chemical assays. The statistical significance of the linear grade distribution data obtained by optical image analysis was assessed and, for a given accuracy, the number of particles required to obtain an unbiased representation of the sample was determined.
Thermodynamic Characterisation of Microcrystalline and Microfine Cellulose Powders
Authors: Stanley‐Wood Nayland
Published: December 2004

Cellulose produced by different processes. (Spray dried and comminuted) have been characterised by low temperature (77K) nitrogen adsorption to determine the specific surface areas, micro‐ and meso‐porosities together with the thermodynamic properties of the Polanyi surface potential and heat (enthalpy) of adsorption.

These physico‐chemical and thermodynamic parameters are then correlated with the physico‐mechanical properties of compactability to indicate the bonding strenghts of microcrystalline and microfine celluloses.
Fine Particle Representations
Authors: Luerkens David W.
Published: December 2004

A general three dimensional analytical mathematical method of quantitative particle representation is presented. The resulting analytical representations are capable of quantitatively representing the three dimensional boundary morphologies of a broad range of particles. This paper summarizes some of the more often encountered particle morphologies prevalent in the micro world.
Fraunhofer Diffraction by Random Irregular Particles
Authors: Jones Alan R.
Published: December 2004

A statistical model is developed for Fraunhofer diffraction by random irregular particles. This is described in terms of a distribution function for radii and a correlation function in the surface. Results are presented for a variety of particle types, and the consequences to particle sizing discussed. Comparison with a “best” sphere suggests a radius based on the average 〈Rn〉 where n > 3.
Mie Scattering near the Critical Angle
Authors: Fiedler‐Ferrari Nelson , Nussenzveig Herch Moysés
Published: December 2004

Complex angular momentum theory is applied to the problem of high‐frequency critical light scattering by a spherical cavity near the critical angle. The main contributions to the scattering arise from a critical domain close to critical incidence. The results are in good agreement with the exact Mie solution.
Particle Sizing by Laser Light Diffraction: Improvements in Optics and Algorithms
Authors: Kouzelis Dimitris , Candel Sebastien M. , Esposito Emile , Zikikout Souad
Published: December 2004

A major problem encountered in particle sizing by laser light diffraction concerns the inversion of the diffraction pattern measured in a given experiment.

Conventional methods for solving the linear system obtained can not be used in this problem, because the matrix is ill‐conditioned and also because the diffraction pattern is usually determined with a low resolution annular diode detector. These problems may be solved with up to date optical detectors (linear CCD‐arrays comprising 1024 photodiodes) and refined inversion techniques (conjugate gradient method and the analytical formulation due to Shifrin).

These two aspects are described in this paper. Two inversion methods are compared and experimental results are discussed.
Realization of a Concept for the Complete Evaluation of Double Pulse Holograms of Particulate Phases in Flows
Authors: Schäfer Michael , Umhauer Heinz
Published: December 2004

Double pulse holography is, for experimental investigations, an extremely valuable means of measuring transport processes in disperse phases. This method allows the single or two dimensional frequency distributions of particle size, velocity, momentum and energy to be determined for each recorded sub‐collective, with the additional possibility of checking the existence of their correlation. Being an imaging method, the distributions of the particles in space can be displayed along with the instantaneous values of the concentration and particle flux density.

A complete and very exact evaluation of the holographic images, coupled with the certainty of image pairing, is one of the prerequisites of a successful application. The best evaluation in this sense is, at present, produced by a semi‐automatic, interactive system in which the assessment of certain crucial factors is left to an operator.

Although the effort incurred by such a total evaluation is by no means insignificant, it is justified by the profusion of information to be obtained.

The present report explains the whole concept including a programme system with which the primary data is further processed and with which a variety of results may be called up and displayed.
Determination of Particle Size Distribution in Fluids using photon correlation spectroscopy
Authors: Krahn Werner , Luckas Michael , Lucas Klaus
Published: December 2004

Photon correlation spectroscopy (PCS) has been applied to various systems of particles suspended in a fluid. Computer simulations were used to analyse CONTIN, a program for the numerical inversion of the experimental data. Measurements were performed on a spectrometer equipped with a digital correlator. Various suspensions of polysterene latex spheres differing both in size and size distribution were prepared in double distilled water. Further some samples provided by an external institution without prior specification were analysed. Diffusivity measurements on submicron DES (di‐2‐ethylhexyl sebacate) particles in nitrogen were also performed. The results obtained demonstrate the strengths and the limitations of PCS as a method of determining particle size distributions in particle fluid systems.
A Theoretical Interpretation of Meloy's Law of Morphological Coefficients
Authors: Vlad Marcel Ovidiu
Published: December 2004

This note deals with the Fourier representation of particle shape. A frequency distribution pn, n = 1,2, …, expressing the contribution of the different harmonics to the dispersion of the position vector is defined. The Meloy law of morphological coefficients may be derived by optimizing the value of the informational entropy which is attached to pn.
Aerosol Generation Method for Measuring Particles Suspended in Water – Detection of Particulate Impurities in Ultrapure Water and Sizing of Fine Powders –
Authors: Niida Tohru , Kousaka Yasuo , Oda Shinji
Published: December 2004

The method described is based on the fact that the measurement of particles in the gaseous phase is generally easier than that in the liquid phase for fine particles smaller than 1 μm in diameter. The system consists of a liquid nebulizing unit, evaporator, condenser, mixing diluter and two different aerosol sizing instruments. It has been found that this method can continuously detect particulate impurities in ultrapure water in situ and can measure the size distribution of fine powders in the submicron particle size range down to about 0.05 μm.
Determination of Particle Size Distribution Parameters using a Laser‐Scattered Light Spectrometer
Authors: Blum Klaus , Fissan Heinz
Published: December 2004

A method based on the measurement of scattered light intensity distributions is demonstrated to be able to determine directly the particle size of monodisperse supermicron‐size particles. In all other cases of a particle cloud, information about the size distribution can be acquired from comparison of measured and calculated intensities as a function of scattering angle. This indirect method is only applicable if the assumptions made in the theory used for comparison are fulfilled. Therefore, the method is limited to spherical particles with known refractive index. The type of size distribution also has to be known. In the cases considered a log‐normal size distribution was assumed. The uncertainty of the result increases with increase in the number of parameters that have to be determined. The method seems to be limited to unimodal distributions described with two parameters.
Sizing of Submicron Aerosol Particles by the Whisker Particle Collector Method
Authors: Schäfer Hans J. , Pfeifer Hans J.
Published: December 2004

Samples of an alumina powder aerosol were collected on whisker particle collectors and analysed following an improved evaluation scheme which allows the empirical size distribution to be corrected for the effect of a non‐uniform collection efficiency. The measurement results are given in terms of log‐normal distribution functions. Some ambiguity was encountered in interpreting particle aggregates that were found on the whisker collectors. By including the results of laser light‐scattering experiments in the size analysis, this ambiguity was removed. Advantages and disadvantages of the whisker collector concept compared with light‐scattering methods are discussed.
Experimental Characterization of Fineparticle Profiles Exhibiting Regions of Various Ruggedness
Authors: Kaye Brian H. , Clark Garry G.
Published: December 2004

In previously reported studies it has been shown that a rugged two‐dimensional fineparticle profile boundary may exhibit different ruggedness at different levels of scrutiny. The different types of ruggedness can sometimes be described by a boundary fractal dimension the magnitude of which can be related to the physical processes which formed the fineparticle. New data illustrating this fact is presented. Detailed examination of some rugged fineparticle boundaries and similar structures suggests that some boundaries exhibit more than one level of ruggedness around the perimeter of the profile. Data illustrating this fact are presented. The possible physical significance of the multifractal structure around the perimeter of a fineparticle profile is discussed. The need for objective criteria to be followed when splitting profiles into regions of different ruggedness is discussed. The possibility of basing the partition algorithm on the inspection of the sequential chord length generated in an equipaced exploration of the perimeter is suggested.
Regularized Inversion of Correlation Functions in Dynamic Light Scattering
Authors: Dhadwal Harbans S.
Published: December 2004

A linear regularized technique, requiring no a priori information, is described for the inversion of correlation data obtained from dynamic light scattering measurements of polymer/colloidal suspensions. The procedure allows the determination of the characteristic linewidth distribution function, which is normally the first step towards obtaining a particle size distribution.
A Light Scattering Instrument to Discriminate and Size Fibres Part 1: A theoretical description using the RGD approximation
Authors: Jones Alan R. , Savaloni Hadi
Published: December 2004

As part of the development of a light scattering instrument to detect fibres, scattered light from finite cylinders which are exposed to light at arbitrary orientation is studied using the Rayleigh – Gans – Debye approximation. Form anisotropy, which is crucial to the performance of the instrument, is allowed for by using the Shifrin modification in which the elemental volumes are considered to be prolate spheroids. For long cylinders this is compared with van de Hulst's model in which the rigorous theory for an infinite cylinder is modified by Fraunhofer diffraction on the length. For very short cylinders comparison is made with the Mie theory for spheres.
A Light Scattering Instrument to Discriminate and Size Fibres. Part II: Experimental system
Authors: Jones Alan R. , Savaloni Hadi
Published: December 2004

A Light scattering technique is described which can discriminate, size and count airborne fibres down to 1.6 μm diameter. The results are compared with Mie theory for spheres and two models for finite cylinders based on the Rayleigh‐Gans‐Debye approximation and rigorous infinite cylinder theory modified by Fraunhofer diffraction on the length.
The Linearity and Response of Focussed Apertures
Authors: Cowan Mark P. , Harfield John G.
Published: December 2004

Practical experience of particle size analysers using the Coulter principle shows that for measurements made over a range of 2% to 60% of the aperture diameter, the aperture responds linearly to particle volume at least for spheres. In this paper it is shown that the response of a focussed aperture is not significantly different from an unfocussed aperture. It is also shown that a simple linear equation of response successfully applied to a COULTER COUNTER® model ZM in a previous paper, can be used to predict the calibration constant of a new wide range instrument, the COULTER® MULTISIZER.
Improved Accuracy in the Measurement of Particle Size Distribution with a coulter counter equipped with a hydrodynamically focused aperture
Authors: Göransson Billy
Published: December 2004

It is well known that broadening of the observed particle size distribution occurs both at the finer end and at the coarser end of the distribution when using the Coulter Counter. This problem can partly be overcome with the aid of electronic pulse editing. However, it has been found that the accuracy can be further improved when the Coulter Counter is equipped with a hydrodynamically focused (HDF) aperture. The standard deviations of the main peaks of samples with diameters of 5.0, 10.2, 15.1 and 20.0 m̈m decreased by 21%‐49% with HDF. HDF also prevents artefacts at the fine side of the main peak that originate from particles re‐entering the sensing zone of a standard aperture after they have passed through it. In the experimental model used i.e. a silica sample with a diameter of 15.6 m̈m, the estimate of small particles (>10 μm) decreased from 6.5% to 0.4%.
Use of the Laser Diffraction Technique for Particle Size Measurement at high suspension densities
Authors: Ulrich Joachim , Stepanski Manfred
Published: December 2004

A laser diffraction technique for the on‐line measurement of crystal growth rates was developed. The crystal growth experiments were executed in a fluidized bed apparatus with a specially designed measuring chamber. It is typical in crystallization from solutions to deal with non‐spherically shaped particles at high suspension densities (3‐25 Vol.‐%). The results achieved in a first approach with commercially available instruments were not understandable. It was shown that the particle size distributions from experiments at high suspension densities depend on the volume concentration. This effect was examined by experiments with constant particle sizes and different volume concentrations.

If the volume concentration is detected and used to correct the results achieved for the particle size distribution, understandable and reproducible results can be obtained.

The necessary correlation function for the measurements at high suspension densities is introduced.
Technologically Relevant Particle Shape Analysis
Authors: Drescher Sigrun , Heidenreich Eberhard , Müller Gerhard
Published: December 2004

The current state in shape analysis is distinguished by a number of characterization methods, but the great variety of specific shapes complicates the selection of parameters that are relevant for a particular problem. Therefore, the preferred approach is to characterize single particles "free of presupposition" and to select technologically relevant parameters using cluster and discriminance algorithms.

Parameter vectors including elongation, bulkiness, fractal dimension and area‐equivalent diameter are calculated on the basis of image analysis. First applications to bacteria and agricultural freestuffs exemplify the concept and illustrate that technologically relevant particle shape analysis permits the classification of single particles and the quantification of property functions.
Standard Media for Particle Size and Number‐Density Calibrations in single, multiple and dependent scattering
Authors: Guidt Jean‐Bernard , Toulouzan Jean Noël Le , Thioye Massamba , Gouesbet Gérard
Published: December 2004

Two kinds of standard media for particle size and number‐density measurements and calibration are described. Although the main concern is multiple scattering situations, they might also be useful for single and dependent scattering. One medium is made of particles embedded in a solid polymer matrix and the other of particles embedded in a gel. Transmittance measurements at two wavelengths (visible and far‐infrared) are used to exemplify the use of these media.
Dual‐Cylindrical Wave Method for Particle Sizing
Authors: Naqwi Amir A. , Liu Xiao‐Z. , Durst Franz
Published: December 2004

A new laser Doppler method for particle sizing has been developed. In contrast to the standard phase Doppler technique, which uses scattering from plane waves for a measurement, the proposed method employs cylindrical waves of incident light. The main advantage is that signal frequency, instead of the signal phase, becomes a function of particle diameter and a standard frequency measuring device may be used as a signal processor. The advantages of spectrum analysis as the signal processing method are highlighted.

The laws of geometrical optics applied to the present scattering problem provide a relationship for the frequency of the collected signal which is expressed as the sum of two terms, the conventional Doppler frequency and the "anisotropic frequency", which is directly dependent on the particle size. These theoretical assertions were examined experimentally. Measurements on glass and metal particles of known diameters showed good agreement with the theory.
Calculated Characteristics of Droplet Size and Velocity Distributions in liquid sprays
Authors: Li Xianguo , Tankin Richard S. , Renksizbulut Metin
Published: December 2004

Predictions of the droplet size and velocity distributions in sprays under isothermal conditions are reported. The calculations are based on the maximum entropy formalism, complying with the conservation laws of liquid mass, momentum and energy. This theoretical approach considers only the macroscopic quantities about the atomization processes, without resorting to the details of the liquid breakup processes such as the onset and growth of instabilities. The derived joint droplet size and velocity distribution function depends on the Weber number as well as the liquid mass, momentum and energy source terms.

These parameters represent the conditions under which the atomization occurs. The droplet velocity distributions are truncated Gaussian distributions for any specific sizes. The nondimensional Sauter mean diameter decreases slightly with the Weber number and then approaches an asymptotic constant. The calculated values of D21/D30 are very close to unity which agrees with the experimental observations. The computations also show that the atomization efficiency is very low; less than 2.6 percent.
Use of One‐Parameter Models for the Assessment of Particle Interactions by photon correlation spectroscopy
Authors: Finsy Robert
Published: December 2004

The use of very simple one‐parameter models of particle interactions for the analysis of the concentration dependence of the collective diffusion coefficient as determined by photon correlation spectroscopy is illustrated by measurements on two different systems. In one, a micro‐emulsion, attractive interactions are dominant whereas in the other, a silica dispersion, repulsive interactions play the major role.
The Use of Simulated Fractals in Particle Characterization
Authors: Gentry James W.
Published: December 2004

The principal focus in this paper is the development of a general method to simulate irregulary shaped particles whose perimeters are fractal. It is shown that this method can produce a particle of almost arbitrary fractal dimension. The Fourier components of these fractals are then computed. It is shown that these components were either independent of the fractal dimension or that any dependence is less important than other properties of the cluster such as symmetry and aspect ratio.
Sizing Nanoparticles by Means of Elliptically Polarized Scattered Light: A suggested method
Authors: Bohren Craig F.
Published: December 2004

Given the paucity of optical methods for sizing nanoparticles (those between 1 and 100 nm), more methods are needed if, as has been predicted, such particles have a bright future. Linearly polarized light is transformed into elliptically polarized light upon scattering by small spheres at 90°. The resulting circular polarization increases as the fifth power of particle diameter and the shift of the azimuth of the vibration ellipse from the vertical increases as the square if the particles are negligibly absorbing. Titanium dioxide spheres (in air) with diameters between 20 and 120 nm give circular polarizations between about 10−5 and 10−1 for incident light of wavelength 450 nm. The corresponding azimuth shifts (in radians) lie between about 10−2 and 1. These values are within reach of experimental techniques based on polarization modulation. Metallic spheres yield much larger circular polarizations and azimuth shifts (with signs opposite those for negligibly absorbing spheres), both of which increase approximately as the square of particle diameter.
Particle Dispersion in Turbulent Flow: The effect of particle size distribution
Authors: Sommerfeld Martin
Published: December 2004

The measured velocity fluctuation of particles in dispersed twophase flow systems is discussed and an interpretation of particle velocity statistics is given. Besides the turbulent velocity fluctuations resulting from the particle's response to the fluid turbulence, two additional apparent fluctuation components may be distinguished, caused by inertial effects of the particles and by a polydisperse particle phase.

Especially for larger particles inertial effects may become important and therefore the particle motion in the flow field is strongly governed by the inlet conditions, namely the instantaneous particle velocity. Therefore, the measured axial particle velocity fluctuation at a given location may be considerably increased as particles from different starting locations with different initial velocities may cross the same measuring point. This dynamic particle behaviour is demonstrated by the numerical simulation of particle trajectories in a given flow field. The results show the importance of including appropriate inlet conditions for the numerical prediction of particulate two‐phase flows.

Further, in experimental realizations of particulate two‐phase flows, the particles usually exhibit a certain size distribution. Owing to the different responses of the different sized particles to both the mean flow field and the turbulence characteristics of the flow, the measured particle velocity fluctuations are higher than in the comparable monodisperse case. Therefore, the particle size distribution was taken into account in the present numerical calculations in order to obtain results which are comparable to the corresponding experiments. In this numerical simulation the particle mean velocity and the rms value of the velocity fluctuation were obtained by averaging over the whole particle size distribution and then compared with the measured values. Calculations are presented for two different shaped particle size distributions with a different mean size and compared with calculations with a monosized particle material and experimental results.

Further, the behaviour of the different sized particles in the particle size distribution is discussed by considering the changes in the particle size distribution and the particle velocity distribution throughout the flow field.
The Kinetics and Shape Factors of Ultrafine Dry Grinding in a laboratory tumbling ball mill
Authors: Austin Leonard G. , Yekeler M. , Dumm Timothy F. , Hogg Richard
Published: December 2004

The kinetics of batch grinding quartz from a feed of 600 by 425 m̈m to a product of 80% less than 10 m̈m have been determined using screening and laser diffractometer sizing for size analysis. The specific rates of breakage decreased by a factor of about three when the material became less than about 100 m̈m in size, but the primary breakage distribution function also changed to give proportionately more fine material, so that the grinding efficiency expressed as the development of surface area (B.E.T.) per unit of energy input did not decrease. Analysis of the shape of the particles in the 25 × 38 m̈m size range showed that particles of this size produced by roll crushing or by 8 minutes of grinding of a 425 × 600 m̈m feed were not different but at long grinding times the particles were rounded. This suggests that the breakage mechanism changes to give more chipping and abrasion and less disintegrative fracture. As the material approached the ultrafine size range it adhered to the mill case and there was no further size reduction. However, a technique for striking the mill case to dislodge the particles was successful in allowing further grinding to 40% by weight less than 2 μm.
Optical Levitation Experiments for generalized lorenz‐mie theory validation
Authors: Gréhan Gérard , Guilloteau François , Gouesbet Gérard
Published: December 2004

Generalized Lorenz‐Mie theory (GLMT) is validated by comparisons between theoretical results and experimental optical levitation data. Selected results are presented.
Bipolar Ion and Electron Diffusion Charging of Aerosol Particles in high purity argon and nitrogen
Authors: Wiedensohler Alfred , Fissan Heinz J.
Published: December 2004

The bipolar diffusion charging process is studied theoretically for aerosol particles in high purity argon and nitrogen. The Fuchs theory is extended by the incorporation of the free electron charging of the aerosol particles. The ion parameters for positive and negative ions are assumed to be identical. The influence of the free electrons explains the differences between the mean mobility and mean mass of negative and positive ions. The ratio of the electron number concentration to the number concentration of negative ions is used to fit the curves, calculated by the extended model, to the experimentally determined bipolar charge distribution in argon and nitrogen. The extended Fuchs model was found to be rather insensitive to variations in the mobility and mass compared with the model with four different ion parameters. Further experimental studies of the bipolar charge distribution in a gas mixture of pure nitrogen and sulfur hexafluoride, SF6, indicate the importance of the free electrons in the bipolar diffusion charging process.
Measurement of Size, Number Concentration and Velocity of Aerosol Particles using an optical particle counter
Authors: Sachweh Bernd
Published: December 2004

An aerosol measurement instrument is presented which allows for the simultaneous measurement of the size distribution, number concentration and velocities of particles. A commercial optical particle counter (OPC) was modified in terms of optics and signal evaluation to provide the required measurement information. The design of this instrument allows the definition of a cubic measuring volume by purely optical means. This is achieved by an aperture/lens system which projects a sharply defined light beam into a stream of aerosol flow. Light scattered from single particles at average angles of 90° is collected by two opposite receiver units, each projecting light on to a separate photomultiplier. The intensity of the scattered light with this instrument is found to be an unambiguous function of the particle size. The total number of particles detected per unit time results in the particle flux. The particle velocity can be calculated, in principle, through the correlation of the signal length and the optical length of the measuring volume, provided that the particles have a straight trajectory through the measuring volume and the measuring volume length in the mean flow direction is well defined. The absence of sharpness in real optical projections effects a border zone of definite length, in which the illumination declines to zero. This leads, together with the low‐pass filtering of the particle signals, to an increase in the length of the signal slopes, causing some difficulties in the determination of the signal length. A digital signal evaluation technique was developed that renders possible the clear differentiation between the slope and the kernel region of the signal. The latter represents the motion of particles through the completely illuminated region, which can be a more accurate parameter to define the signal length. In addition to the signal length determination, a cross‐correlation technique was tested for its potential to obtain particle velocity. the instrument has two interlaced measuring volumes of nearly the same size, which are shifted for this special application in the main flow direction by 20 μm. The phase difference between the signals from the two photomultipliers, together with the optical distance, yields the particle velocity.
Particle Sizing by Dynamic Light Scattering: Noise and distortion in correlation data
Authors: Ross Douglas A. , Dimas Nicholas
Published: December 2004

Two undesirable effects occur in particle sizing by dynamic light scattering; statistical noise, and distortion of correlation data. Statistical noise in the correlation data, caused by estimating the autocorrelation of scattered laser light by a time average, leads to non‐physical artifacts in the resulting linewidth distribution. These may be removed by regularization, computer modeling, or other techniques. The regularized kernel function for inverting the Laplace transform is calculated, and used to illustrate the problem of noise. Correct choice of the regularization parameter gives the minimum overall error. It is found that excessive error occurs unless the linewidth distribution is modeled over a finite range. Analytical models for the linewidth with finite range, based on the beta distribution of probability theory, are given.

Distortion of correlation data may occur in three ways, through a focused or otherwise nonuniform laser beam in the optical system, by insufficient bit resolution in the quantized detection of scattered laser light, or by calculating a first order field autocorrelation from a second order intensity autocorrelation. Unlike noise, distortion cannot be removed by any known methods, since the exact nature of the distortion is unknown. Several examples illustrate how distortion can lead to artifacts in the linewidth distribution which could easily be misinterpreted as segments of a size distribution, not present in the physical sample.
In‐Line Particle Size Determination for Jet Agglomeration Processes
Authors: Schuchmann Harald , Schubert Helmar
Published: December 2004

In jet agglomeration plants, powders are agglomerated to obtain good instant properties. The free‐falling initial material is wetted in a spray cone by droplets or in a steam jet by condensation at the particle surface. In a subsequent region of high particle concentration, collision between particles occurs and agglomerates form, if the forces of adhesion are strong enough. A commercial measurement device, working according to the principle of Fraunhofer diffraction, was modified for in‐line application. It was used to measure particle size distributions and concentrations of solid particles and droplets in jets. A model is presented to calculate local particle sizes by means of mass balances from integral measurements over large volumes. The results of in‐line particle size and agglomerate size analyses show the practical importance of dry agglomeration during transport and lead to a better understanding of the subsequent wet agglomeration process.
Light Scattering by Anthophyllite‐Crocidolite Asbestos Fibers. Part I: The domain of convergence of the EBCM theory
Authors: Lapalme René , Patits Tom A. J.
Published: December 2004

The Extended Boundary Condition Method (EBCM), also known as the T‐matrix method, is used to compute exactly the scattered intensities from homogeneous isotropic circular cylinders characterized by relative refractive index N, diameter D and length L. The domain of convergence of the method regarding the parameters N, D, L is established. The effect of the geometry of the fiber ends on the scattered intensities is considered. The incident field is assumed to be a linearly polarized plane harmonic wave.
Cessation of Aggregate Growth
Authors: Amal Rose , Raper Judy A. , Waite T. David
Published: December 2004

Various methods are available for reducing or ceasing growth of aggregating suspensions including the addition of highly charged adsorbents (such as gelatin), reduction of ionic strength by dilution, increase in surface charge by alteration in pH and reduction in suspension temperature. The effectiveness of each of these methods in stopping the aggregation of colloidalhematite without altering the aggregate size distribution is examined in this study. Reduction in aggregate temperature is found to be a particularly effective way of stopping the aggregation of hematite while preserving size distribution information.
The Characterisation of Particles Using the Settling Rate dependent movement in two phase flows
Authors: Leschonski Kurt
Published: December 2004

The drawback of conventional sedimentation methods, mainly their extremely long sedimentation time for small particles, can be overcome in two phase flow systems. In this paper several principles which permit the rapid determination of settling rate distributions are discussed. Settling rate distributions can be determined from the accelerated particle movement in a flow of constant velocity at low and high solids concentrations. Another system uses accelerated flow at low solids concentrations. The best utilisation of settling rate applications have socalled cross flow systems as set up in a stagnation point flow, in a flow round a bend, or in the decelerated particle movement perpendicular to a flow of constant velocity.
Dense Monolayers of Monodisperse Opaque Spheres: Transmission and diffraction in the fraunhofer domain
Authors: Riebel Ulrich , Hickl Peter
Published: December 2004

The transmission and diffraction of radiation through dense monolayers of monodisperse opaque spheres were studied for the Fraunhofer domain. Theoretical considerations, numerical calculations and experiments on ultrasonic transmission and on laser light transmission and diffraction yielded corresponding results. Complementary studies included the cases of sterically non‐interacting particles (by numerical simulation) and of small particle size parameters (by ultrasonic extinction). Transmission was found to be, in general, a non‐linear function of the monolayer density. Secondary effects on the transmission can be attributed to the effect of the monolayer structure (characterized by the pair correlation function) on the angular distribution of diffracted intensity. The results were found to be in accordance with experimental results on extinction in three‐dimensional systems.
Neural Networks for Flow Regime Identification with dry particulate flow
Authors: Bidin Abdul Rahman , Green Robert G. , Shackleton Mary E. , Taylor Richard W.
Published: December 2004

This work on imaging of particulate processes using electrical charge tomography uses two basic techniques: the multi‐sensing of electrical charge in a cross‐section of the flow pipe and a neural network based flow regime identification system to aid in the image reconstruction process.

A measurement system, consisting of sixteen sensors, placed at equal distance from each other around the boundary of a circular 100 mm bore pipe, is used to determine the voltage profile of the flow for several artificially produced flow regimes: full, annular, core, half and stratified. A sand flow system is used to produce these different flow regimes, which are created artificially by using baffles of different shapes that obstruct the sand flow.

The voltage profile from the sixteen sensors gives spatial information of the flow regime. These profiles are normalised and formed into patterns that are presented to a Kohonen neural network for classification. Two regime classification between clearly distinct regimes gives an accuracy of identification of 85%. Classification of closely similar patterns show much less accuracy of 30%.
Ensemble and Single Particle Laser probe sizing results for gas atomized zinc powders
Authors: Boyko Christina M. , Le Tuyet H. , Henein Hani
Published: December 2004

On‐line characterization of powder and droplets during gas atomization of molten metals and alloys offers extensive opportunities for real‐time process monitoring and control. The capability to make on‐line measurements can significantly reduce tedious and costly powder classification, which, currently, is always carried out subsequent to the atomization process. Two laser‐based particle sizing instruments, the EPCS (ensemble instrument) and PCSV (single particle instrument), were used during gas atomization of zinc with a double Coanda nozzle configuration. The laser instruments were positioned in the duct leading from the bottom of the atomization tower to the powder collection cyclone. The effect of gas to metal ratio on particle size was studied by varying the atomization gas pressure from 0.69 MPa to 1.03 MPa. Air was used as the atomizing gas for some of the 0.69 MPa runs, while nitrogen was used for all of the higher‐pressure runs. Experimental apparatus and procedures for atomization and on‐line powder sizing with the EPCS and PCSV are described. EPCS and PCSV measurements, which were compared with standard sieve analyses, indicate that the ensemble instrument is a good candidate for on‐line process monitoring and control.
Generalized lorenz‐mie theory and applications
Authors: Gouesbet Gérard
Published: December 2004

Many optical sizing techniques rely on particle/laser interactions. The classical Lorenz‐Mie theory describing sphere/plane wave interactions is therefore misleading when designing instruments and processing data when the particle size is not small enough with respect to beam diameters. In such cases the use of the generalized Lorenz‐Mie theory is required. After summarizing essential features of the generalized Lorenz‐Mie theory for sphere/arbitray wave interactions, this paper describes applications of the theory with some emphasis on the analysis of phase‐Doppler anemometers.
Coherent Scattering by Multiple Particles in Phase Doppler Interferometry
Authors: Sankar Subramanian V. , Ibrahim Khalid M. , Bachalo William D.
Published: December 2004

A theoretical model has been developed for studying the response of the phase Doppler interferometer when multiple particles are simultaneously present within the measurement probe volume. The developed model incorporates the geometrical optics theory for describing the coherent interaction between the scattered light signals of multiple particles, eachhaving different size, velocity, trajectory, and arrival time. The resulting Doppler signal is processed by a theoretical signal processor which can simulate the performance characteristic of different signal processing schemes that are widely used in phase Doppler interferometry, namely, zero‐crossing counter, covariance, autocorrelation and DFT parocessors. The application of the developed model for studying the coherent scattering by two particles has been specifically addressed in this paper. It has been shown that a DFT processor can be used to simultaneously measure the size and velocity of the two particles in most instances. However, for more than two particles, the signal processing scheme becomes more complex because of a quadratic increase in the beat frequency components.
Particle Image Velocimetry Applied to a Spray Jet
Authors: Brandt Andreas , Merzkirch Wolfgang
Published: December 2004

Experiments are described in which particle image velocimetry (PIV) is applied to the measurement of liquid droplets in a spray jet. The two velocity components in planes formed by the light sheet originating from a double‐pulsed ruby laser are determined. The PIV records are evaluated with the method of Young's fringes. It is shown that this procedure allows the simultaneous measurement of the droplet size within a certain size range.
Design and Performance of an Ultrasonic Atomization System for experimental combustion applications
Authors: Lacas François , Versaevel Philippe , Scouflaire Philippe , Coeur‐Joly Gérard
Published: December 2004

Although common atomizing systems efficiently produce sprays, a range of droplet sizes is generally obtained and the distribution is often difficult to control in terms of liquid or gaseous flow rates. It is shown that an alternative system, based on ultrasonic surface instabilities, is well suited for experimental applications where all parameters have to be controlled. Technological aspects of ultrasonic atomization are described and the droplet spray produced by an ultrasonic atomizer is characterized experimentally.
Particle size Effects on Optical Transport through strongly scattering media
Authors: Dogariu Aristide , Uozumi Jun , Asakura Toshimitsu
Published: December 2004

Measurements of transmission and enhanced backscattering from powder beds of α‐AI 2O3 consisting of particles with different average sizes are reported. The values of the mean free path and the absorption length, as inferred from these measurements, are compared and good agreement between the two measurement is found when the internal reflections are properly taken into account. A particle size measurement method is suggested on the basis of the linear dependence found experimentally between the transport mean free path and the mean particle size.
A Light Scattering Study of Coal Combustion in a Drop Tube Furnace
Authors: Card Jacqueline B. A. , Jones Alan R.
Published: December 2004

A light scattering method has been devised to discriminates between coal and fly ash and measure particle size. Sizing was performed by the measurement of forward scattered intensity, and discrimination was displayed by the ratio of the intensities of crossed to parallel polarisations at a scattering angle of 160°. The technique has been applied to a study of coal combustion in a variable length drop tube furnace. It has been demonstrated that the development of the size distribution can be followed as a function of residence time. Further, it is indicated that there is a simple correlation between the polarisation ratio and the carbon content of the ash. This leads to the possibility of monitoring combustion efficiency in industrial furnaces.
Computerised Perimeter Mapping and the Measurement of Fractal Dimensions
Authors: Adler Jeremy
Published: December 2004

A method is described for mapping the perimeter of shapes as a sequence of connected X & Y coordinates. It operates by tracking, in tandem, along a dilated outline of the shape and the true outline, maintaining contact between both tracks. This combination permits the complete mapping of binary shapes regardless of their complexity. The resulting sequence of X & Y coordinates form an 8‐connected map of the outline, which can then be used to obtain fractal dimensions using structured walks. The method requires a digitised image that has been converted into a binary form and the ability to read the values of individual pixels from the digitised binary image. In addition a number of approaches for increasing the efficiency of the twin tracking algorithm are outlined.

Obtaining fractal dimensions from a structured walk based on a fully mapped perimeter increases the accuracy of the measured fractal dimensions, extends the range of step sizes over which measurements can be made and permits a highly detailed examination of the perimeter.
Continuous Mixing of Fine Particles
Authors: Weinekötter Ralf , Reh Lothar
Published: December 2004

The efficiency of reactors fed with particulate mixtures is often reduced by segregation of solids. Placing continuous mixers directly ahead of a reactor may be a solution to this problem. The performance of such mixers can be monitored for appropriate binary solids systems with an optical in‐line measuring system. The tracer concentration (SiC or Irgalite) in Al(OH)3 was registered with high time resolution, thus making possible an extended statistical analysis of mixing processes using the power density spectrum. Experimental mixers with a maximum ‐throughput of 300 kg/h were fed with a fluctuating tracer concentration and the variance reduction ratios were determined. A model was developed that takes into account feeding constancy, residence time distribution and the limited homogeneity of particulate mixtures. Diagrams for continuous solids mixing processes are derived therefrom. They demonstrate the importance of high‐accuracy feed‐rate control.