摘要:

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

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070112

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

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 atRe= 1.54 × 105to 4.2 × 105by 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 freque

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070113

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe 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 r

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070114

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractInversion of the Laplace integral equation, used in the laser scattering measurement of colloidal particle size distributions, presents sever numerical and experimental difficulties. In the presence of noise the variance of the inversion integral is infinite, indicating maximum uncertainty in the accuracy of the inversion. The regularized inversion of the Laplace intergral equation provides a convenient computational algorithm which requires no a priori knowledge of the unknown linewidth distribution. Using the eigenfunction decomposition of the Laplace kernel, the spectral properties of the regularized inversion may be seen.Regularized inversion represents a type of low pass filter which preserves the properties of the inversion spectrum at low frequencies, but provides a cutoff at a point controlled by the regularization parameter. This filtering reduces the variance of the inversion to a finite value. Regularized inversion is somewhere between optimal filtering and the abrupt truncation used in singular value decomposition and other similar methods. Two examples, a monodisperse and a bimodal linewidth distribution, are used to compare the performance of regularized inversion to that obtained through an optimal filter.

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070115

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe 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.

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070116

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractA theoretical model for the interaction of charged particles with an alternating current field is developed. This model permits the determination of the particle size distribution by a numerical nonlinear iterative method. Results of numerical simulations are presented and discussed. Restrictions on the applicability of the model as an on‐line measuring system are pointed ou

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070117

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070118

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe analysis of particles in the sub‐micron range by sedimentation field flow fractionation (SFFF) is not new, but its commercial exploitation is recent. This inevitably will lead to a rigorous evaluation of the technique by many laboratories, for many applications, as well as to rapid development.This paper describes first an evaluation of the new commercial instrument using both ideal and real materials. These experiments lead to a discussion of the software package and of the influence of experimental conditions. A particular study is described of the combination of the SFFF technique with that of quasi‐elastic light scattering. The paper concludes that SFFF now offers the technology for realistically measuring particle size distributions at high resolution in the submicron size range. The analysis time is in the order of one hour, but can be reduced at the expense of resolut

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070119

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractGiven 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 10−5and 10−1for incident light of wavelength 450 nm. The corresponding azimuth shifts (in radians) lie between about 10−2and 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 di

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070120

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractUsing computations based on Mie scattering theory, the influence of the size and shape of the receiving aperture on the signal properties of a phase/Doppler system is examined. For circular apertures exceeding a certain size limit, it is shown that the signal phase is non‐monotonic with respect to the particle diameter and exhibits abrupt changes of 180° at certain values of the diameter. This difficulty may be overcome by using rectangular apertures with appropriate aspect rati

ISSN:0934-0866    

DOI:10.1002/ppsc.19900070121

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY