bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sampling Probes as Precollectors for Cascade Impactor Measurements on Aerosols in Gas Flows
Authors: Bürkholz Armin 
Published: December 2004

AbstractIn the measurement of dust particles or droplets with cascade impactors, coarser particles are lost both in the impactor and in the sampling train. In order to reduce these losses and to recover this coarse fraction, the use of a precollector is recommended. As a rule, measurements in industry must generally be made with sampling probes. It is, therefore, reasonable to combine the probe and precollector.We measured the particle losses which occur in probes as a consequence of sedimentation and inertial forces. Wall losses through turbulent deposition seem to play only a minor role. By adjusting the gas inlet to a nozzle‐impaction plate sampling system, the coarse fraction can be collected and assessed quantitatively. Particle losses in the subsequent probe and impactor can, thus, be kept very low.By using nozzles of different apertures and by varying the gas flow rate, isokinetic sampling conditions can be achieved. The collecting properties of the nozzle‐impaction plate system inlet correspond very closely to those predicted by impaction theory. A special adaptation of the nozzle can give a cut point of the precollector close to 10 microns. Cut points at greater particle sizes are not recommended because of uncontrollable particle losses in the probe.
Laser Beam Scattering by Individual Spherical Particles: Numerical results and application to optical sizing
Authors: Maheu Bruno , Gréhan Gérard , Gouesbet Gérard 
Published: December 2004

AbstractStarting from the expressions of the Generalized Lorenz Mie Theory (GLMT), this paper first presents numerical results for the specific gn coefficients involved in Gaussian beam scattering theory. These results are computed in the special case where on‐axis scatterers are considered. The localized interpretation of the gn coefficients is then developped and discussed, leading to significant simplifications of the numerical computations. Finally, this localized interpretation is used for comparisons of the Generalized Lorenz Mie Theory with other experimental and theoretical data.
Visible Infra‐red Double Extinction Measurements in Densely Laden Media, New Progress
Authors: Gouesbet Gérard , Gougeon Patrick , Le Toulouzan Jean‐Noël , Thioye Massamba , Guidt Jean‐Bernard 
Published: December 2004

AbstractThis paper describes new progress obtained with an optical technique called V.I.D.E. (Visible Infra‐red Double Extinction) which simultaneously measures mean particle size in the range of 10–120 μm and mean number density in densely laden media (up to 0.1% volume fraction). The underlying theory, taking account of multiple light scattering, is recalled. Simultaneous size and concentration measurements are obtained by simultaneously recording transmittances of the medium at two well chosen wavelengths. Experimental results for suspensions of glass particles in air, are described and discussed. The size of particles given by the technique agrees with that given by optical microscopy and Malvern diffractometry. The V.I.D.E. technique is shown to be very suitable to investigate dense media whose optical thickness is up to nine and for which other techniques fail.
The Phase‐Doppler‐Difference‐Method, a New‐Laser‐Doppler Technique for Simultaneous Size and Velocity Measurements. Part 2: Optical particle characteristics as a base for the new diagnostic technique
Authors: Bauckhage Klaus , Floegel Hans‐H. , Fritsching Udo , Hiller Rüdiger 
Published: December 2004

AbstractSimultaneous size and velocity measurements can be obtained by using photodetector positions of different off‐axis‐angles. But not for all of these positions one receives unambiguous results for the correlation between the phase difference and the particle diameter. This can be clearly demonstrated by the plots of the numerical calculations of the complete Mie's scattering equations. These plots show that for transparent particles which exceed the continuous phase in density at special off‐axis‐angles the situation of light refraction changes into a situation of additional light reflection or vice versa. On the other hand for transparent particles which are less dense compared with the continuous phase and for totally absorbing materials these plots confirm the simplified equations for reckoning the particle diameter by the laws of geometrical optics. The good agreement between these results can also be verified for the backscatter mode for measurements of metallic spheres with an imaginary refractive index.
Optimal Filtering Applied to the Inversion of the Laplace Transform
Authors: Ross Douglas A. 
Published: December 2004

AbstractInversion of the Laplace transform, used in the laser scattering measurement of colloidal particle size distributions, presents severe numerical difficulties. In the presence of noise the variance of the inversion integral is infinite, indicating maximum uncertainty in the inversion. This paper applies the method of minimum variance, or “optimal”, filtering to the eigenfunction spectrum of the Laplace transform, giving an inversion which has finite variance.Spectral decomposition using the eigenfunctions of the Laplace transform gives a representation of the noise and desired signals analogous to the Fourier spectrum used in linear system theory. It is possible to obtain a filtered estimate of the unknown linewidth distribution. The requirement that the variance of this filtered estimate is minimum leads to a Wiener‐Hopf integral equation defining the optimal filter.The results of this paper provide a basis of comparison of all methods of inversion of the Laplace transform, including the extensive literature of colloidal particle sizing by laser scattering or photon correlation.
Investigation of Bubbly Flow by Ultrasonic Tomography
Authors: Wolf Jörg 
Published: December 2004

AbstractComputerized tomography (CT) means reconstruction of pictures from projections taken at different angles. This method is well known in fields such as medical diagnostics and nondestructive testing. The application of CT to gas/liquid flow measurement results in a non‐intrusive method for measuring the spatial distribution of the gas phase in a cross‐section of the flow. In our application the projection data are obtained from measurement of the extinction along a set of ultrasonic rays in this cross‐section, using piezo‐ceramic ultrasonic transducers. The transducers are arranged in a circular sensor array which is directly integrated in the pipe wall of the flow; instead of mechanical rotation, the sensors are sequentially switched.
Prediction of the Drop Size and Velocity Distribution in a Spray, Based on the maximum entropy formalism
Authors: Sellens Richard W. 
Published: December 2004

AbstractA new basis for the prediction of the drop size and velocity distribution in a spray is developed, using the maximum entropy formalism. The prediction considers the imposition of integral conservation constraints for mass, momentum and mechanical energy on the breakup of an undulating liquid sheet. The resulting drop size distribution is similar to the widely used empirical distributions, while the velocity distribution is Gaussian, with a variance that decreases with increasing drop size. Measurements were made in a simple water spray using the Phase/Doppler technique to obtain the joint size/velocity PDF. Photographic measurements were used to obtain an estimate of the geometry of the breakup region, necessary as input to the model. Good agreement was found between the measurements and the predictions, except in the region where drag forces had strongly influenced the distribution. This discrepancy was expected, as drag effects were not included in the model.
Particle Motion in a Turbulent Two‐Phase Dilute Suspension Flow
Authors: Lee S. L. 
Published: December 2004

AbstractPresented here is new unified theory on particle motion in a turbulent dilute two‐phase suspension flow. Results of numerical calculations based on this theory have been found to agree closely with results of recent in‐situ local measurements of a two‐phase flow in a vertical pipe by the use of the non‐intrusive laser‐Doppler anemometry. In particular, a more plausible explanation is now provided for the measured peculiar migratory behaviors of particles in the region close to the pipe wall.
Lower Detection Limit of an Optical Particle Counter in the measurement of particle size distributions
Authors: Sachweh Bernd , Büttner Helmut , Ebert Fritz 
Published: December 2004

AbstractAn Optical Particle Counter with optically defined measuring volume was investigated with regard to an application in the range of fine particles (f.i. water droplets less then 1.5 μm in diameter). Because of a problematic detection behaviour in the examined size range caused by the analogue signal processor, it was necessary to explore signals generated by the measurement system. In view of the results obtained an alternative signal evaluation method was developed on basis of a digital system. The high flexibility of software systems in signal processing rendered possible on the one hand a clear definition of the lower detection limit of the instrument. On the other hand it was possible to lower the detection limit and herewith the size of particles to be resolved. A practical application for the new evaluation technique is given by the measurement of fractional efficiency curves of technical separators and classifiers, which clearly shows the advantages of the system presented. Most recent investigations are concerned with the maximum number concentration detectable with the Optical Particle Counter, which could be increased up to five times.
Comparative Study of some Probability Distributions Applied to Liquid Sprays
Authors: Bhatia Jagdish C. , Durst Franz 
Published: December 2004

AbstractA comparative study of a few probability distributions generally used in describing various spray properties based on droplet size and velocity is described. Four different size distributions and three different coupled distributions, representing jointly size and velocity, are considered. A comparison of the results calculated for eight sets of data, taken from three different sources for the size distribution, and one data set for the joint size and velocity distribution, shows that the log‐hyperbolic function presents the best choice among both one‐ and two‐dimensional distributions.Considerations on one‐ and two‐dimensional probability distributions are followed by a description of the conservation laws and their use in the prediction of the loss of momentum and energy of doplets. Finally, a proposal is made for how the sprays should be studied experimentally and analysed theoretically in order to obtain the maximum possible information. A few suggestions are then provided for further research in this direction.
Determination of Effective Surface Area for the Chemical Reaction of Fine Particulate Materials
Authors: Senna Mamoru 
Published: December 2004

AbstractA concept of effective surface area was defined as a geometrical controlling factor for a chemical reaction involving powdery materials. It is not uniquely determined for the specific material but depends on the sort of chemical reaction as well as the state of agglomeration. Case studies were given for dissolution or decomposition reaction for MgO, Mg(OH)2 and Pb(CO)3 with and without preliminary mechanical activation and granulation. The effective surface area for dissolution is mostly the external surface of the agglomerates, although the internal surface plays a role to some extent, depending on the compactness of the agglomerates.
Fractal Mathematics Applied to Flow in Porous Systems
Authors: Bayles Gary A. , Klinzing George E. , Chiang Shiao‐Hung 
Published: December 2004

AbstractThe Leitz TAS‐Plus image analysis system was programmed to automatically measure both the ‘shape’ fractal and ‘fragmentation’ fractal for various types of fine particle filter cakes. The automated nature of the analysis facilitated the collection of statistically significant volumes of ‘fractal’ data. This data was then revised, where possible, to conventional theories of flow behavior. Several new insights evolved from the study as explained in the following analysis.
Axial‐View Measurements of Particle Motion in a Turbulent Pipe Flow
Authors: Govan Alastair H. , Hewitt Geoffrey F. , Terry John W. 
Published: December 2004

AbstractThis paper describes experimental measurements and numerical predictions of the motion of particles of size 500–800 m̈m diameter in a 20 m long (i. e. 620 pipe diameters) vertical tube. The numerical simulations suggest that the particles attain a fluctuating r.m.s. velocity in a direction normal to the axis of the tube which is at least one order of magnitude less than that of the gas phase turbulence fluctuations. However, the measured values are of the same order as the gas phase turbulence fluctuations (i. e. 0.5 to 1 m/s). This discrepancy is likely to occur because of particle/wall interactions and these were investigated in separate experiments. Although the cause of the measured coefficients of restitution in the normal direction being greater than unity was not finally demonstrated, the results indicated strongly that the effects were due to non‐ideal bouncing of the particles in the presence of particle spin.
Droplet Deposition from a Mist Flow on a Parallel Vertical Wall
Authors: Issapour I. , Lee S. L. 
Published: December 2004

AbstractA primarily experimental investigation of the deposition of droplets from a turbulent two‐phase suspension flow on a parallel vertical wall has been found to be closely related to the ratio of fluctuation velocity of the droplets to that of the flow and the size of the droplets. Data are obtained for an air‐water mist flow parallel to a vertical flat plat at Re = 1.54 × 105 to 4.2 × 105 by the use of a particle‐sizing two‐dimensional reference‐mode laser‐Doppler anemometry technique. Although no rigorous theory can be formulated at present due to the complexities involved, however, an analytical attempt is made in the hope of providing an explanation to the physics of the phenomenon. It is based on an apparent turbulent viscosity of the fluid as felt by the moving particles in a turbulent two‐phase suspension flow and the most energetic eddy frequency of the flow.
Agglomeration and Solution of Particles During Sedimenation Analysis
Authors: Staudinger Gernot , Hangl Manfred 
Published: December 2004

AbstractA basic requirement of particle size analysis through sedimentation is the perfect dispersion of the particles in suspension. The dispersion must be perfect and stable. To ensure this, for a number of solids DIN 66111 specifies sedimentation liquids and suitable dispersing agents and defines an upper limit for the concentration of the solids in suspension. Some instruments require higher solids concentrations than are recommended in DIN 66111. However, there is no simple test to prove the stability of a dispersion with sedimenting particles.An effective method for testing the stability of a dispersion is to make a number of simultaneous sedimentation analyses, measuring the concentration of the particles at different distances from the surface of the liquid. If the dispersion remains perfect, identical particle concentrations have to be measured, when the measuring time is normalized to one distance from the surface (e.g. t1′ = t(h3/h1), t2′ = t(h3/h2) …). From the particle concentration, distance from the surface and time, the particle size distribution can be calculated.If the results of the lower (and hence later) measurement show a shift to the larger diameters, agglomeration has occurred. If the sensing technique is light extinction, then the effect is particularly pronounced.A photosedimentometer with three light beams at distances from the surface of 1.5, 15 and 150 mm was used to demonstrate the effect of agglomeration on particle size distribution and to optimize sedimentation liquids and dispersing agents. An attempt was made to determine the kinetics of agglomeration from the increase in transmission of a light beam through a suspension.
Mean Particle Diameters. Part I: Evaluation of definition systems
Authors: Alderliesten Maarten 
Published: December 2004

AbstractMean particle diameters are important for the science of particulate systems because they provide information on particlesize distributions in such a way that they can be related to physical or physiological processes or product properties. There are different notation systems for such mean diameters which may cause much confusion. This equally applies to their nomenclature. The present paper is concerned with comments on the “Moment‐Ratio” and German (DIN) notations. The Moment‐Ratio notation is recommended for standardization. A more extensive contribution of statistics to the science of particulate systems is recommended.
Error Estimates in the Sampling From Particle Size Distributions
Authors: Paine Anthony J. 
Published: December 2004

AbstractIt is often necessary to estimate the properties of particle size distributions from limited samples taken from large populations. When the distributions are broad, and higher order moments required, as in the case of volume based particle size distributions, the inferred parameters d3,50 (volume median diameter) and GSD (geometric standard deviation) can have high intrinsic errors not immediately obvious to the measuring scientist. We show that there is a critical number of particles, Ncrit, which must be counted or else the error may blow up catastrophically. Ncrit is very sensitive to the width of the distribution, and is approximately proportional to GSD11 We develop formulae to estimate the random sampling error inherent in measured values of the d3,50 and GSD for the log‐normal distribution; compare the predictions to a typical experimental particle size measurement; and then generalize to the median of any arbitrary moment, dr, 50.
Scattered Light Photometer for On‐Line monitoring of size distribution parameters and particle number concentration
Authors: Jerkovic Angelo , Fissan Heinz J. 
Published: December 2004

AbstractA scattered light photometer which monitors the particle number concentration of aerosols is described. The photometer measures the scattered light from illuminated submicron particle clouds with known material properties at certain scattering angles. Intensity ratios in combination with the degree of polarization are used to determine the mean particle diameter and the geometric standard deviation of an assumed log‐normal particle size distribution. The determination of the particle size distribution is based on an algorithm which compares the measured and calculated (Mie theory) relative intensity quantities described. Furthermore, the particle number concentration is monitored from a single absolute intensity measurement at one scattering angle. In order to obtain quantitative results a spherical particle shape is required.
Description of Two‐dimensional Distributions of Particle Size and Particle Velocity of a flowing discontinuous phase by means of special mathematical functions
Authors: Raasch Jürgen 
Published: December 2004

AbstractAs potential approximation functions for measured two‐dimensional distributions, the two‐dimensional normal distribution and the two‐dimensional log‐normal distribution are presented, in addition to mixed forms in which one of the two variables is linearly and the other logarithmically normally distributed. For all four distribution functions, regression curves are calculated, with x being understood as independent and y as dependent variable. The general concept is applied to the specific case of a two‐dimensional distribution of particle size x and particle velocity y. In this context, a number of particularities result from the fact that a distinction has to be made between concentration‐dependent and flux‐dependent measurement.
Image Analysis for Off‐Line Characterisation of mineral particles and prediction of processing properties
Authors: Sutherland David N. 
Published: December 2004

AbstractThe paper discusses the application of image analysis to multiphase mineral particles. The emphasis is on the development of automatic and routine methods which provide reliable data for the process engineer. Optical systems are discussed briefly, but electron beam instruments are shown to offer many advantages for the identification and discrimination of mineral species. Image capture and analysis procedures are described together with the application of the measured data to aid our understanding of the processing properties of particles of complex structure. Examples are given from studies of beach sands, silver minerals, flyashes, ore characterisation, flotation of base metals, grinding and liberation.
Calibration of the electrical aerosol analyzer at subambient pressures
Authors: Romay Francisco J. , Pui David Y. H. , Liu Benjamin Y. H. , Goles Ronald W. 
Published: December 2004

AbstractA commercial Electrical Aerosol Analyzer (EAA, TSI Inc. model 3030) was calibrated experimentally at three subambient pressures (i. e., 0.901, 0.878, and 0.853 atm). Each calibration resulted in a 19 × 11 response matrix and a size dependent sensitivity curve \documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{pA}}{{{\# \mathord{\left/ {\vphantom {\# {cm^3}}} \right. \kern-\nulldelimiterspace} {cm^3}}}}} \right) $\end{document}. The results of the calibration were incorporated into a data reduction computer program for size distribution inversion. The accuracy of the calibration was tested by measuring the size distribution of a NaCl polydisperse aerosol at the three subambient pressures. All the tests gave good agreement in the inverted mean geometric diameter and geometric standard deviation of the aerosol number size distribution.
Determination of Size, Evaporation Rate and Freezing of Water Droplets using light scattering and radiation pressure
Authors: Roth Norbert , Anders Klaus , Frohn Arnold 
Published: December 2004

AbstractTwo independent optical diagnostic techniques for studying the evaporation and freezing of optically levitated droplets are described. In the first technique the size of the droplet is determined by evaluation of the fringe spacing of the light scattered in the forward hemisphere at a scattering angle of 45°. The other technique evaluates the oscillations of optically leviated droplets caused by fluctuations in the radiation pressure. The frequency of these fluctuations is a direct measure for the change of radius with time. In both methods the signals change drastically when freezing of the droplet occurs. Hence the moment of freezing can easily be detected.
Johnson's SB distribution function as applied in the mathematical representation of particle size distributions. Part 1: Theoretical background and numerical simulation
Authors: Yu Ai‐Bing 
Published: December 2004

AbstractAn investigation was carried out of the transformation between the number, length, surface and volume size distributions expressed by Johnson's SB distribution function – the bounded log‐normal distribution function. As is well known, if any of the number, length, surface and volume distributions is log‐normal, all the others will also be log‐normal. Theoretical analysis suggests that the SB function may have a similar property. This was confirmed by a computer‐aided numerical simulation, in which emphasis was given to the transformation between successive order size distributions, i.e. ƒi(x) → ƒi + 1(x) or ƒi(x) → ƒi − 1(x). The numerical results can be applied to the particle size distribution transformation because this transformation can generally be made step by step, for example, ƒi → ƒi−1 (x) → ƒi − 2(x) → … → ƒj(x) for ƒi(x) → ƒj(x) ( i > j).