ISSN:0934-0866    

DOI:10.1002/ppsc.19920090112

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of coincidence errors on the accuracy of fineparticle profile characterization of respirable dust hazard by Image Analysis procedures is discussed. Monte Carlo routines are used to characterize the level of clustering that can occur in a field of view from random chance. The effectiveness of some image processing strategies used to separate touching components of visible clusters are discussed. Monte Carlo routines are also used to explore at what level of space occupancy a monosized population of dust fineparticles being deposited at random has no significant level of stochastic clustering. These studies demonstrate that if reliable information on dust hazards is to be forthcoming from image analysis studies of the deposited dust deposition, measurement routines must change radically from those in current use. It is also pointed out that interpretive uncertainties associated with many previous studies of dust levels to which industrial workers have been exposed may invalidate experimental data reported from the workplace.

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090113

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractOf all methods of particle size analysis determination only microscopy and subsequent image analysis enables accurate, geometrically determined size parameters to be measured. For this reason image analysis is a convenient referee or umpire method against which to compare other techniques.In this study, a series of seven poly(vinyl) chloride (PVC) resins were characterized by optical microscopy and image analysis, sieves, HIAC and Coulter counter. It was not found possible to perform the image analysis measurements without operator intervention with a light pen to separate agglomerates. The PVC particles were far too irregular to enable this task to be performed by erosion and dialation techniques. The errors at 90% confidence associated with the image analysis study were: calibration ± 1.7%, counting statistics ± 1% (max) with a focus and algorithms error which ranged from ½‐3% depending upon the quantity being measured. These numbers gave a total error of ± 2% (ca. one pixel) for equivalent circular diameter (ECD) and ± 4% (ca. two pixels) for object breadth. In general the agreement between the various techniques was quite good suggesting that the object breadth (OB) as measured by sieves was nearly identical to equivalent spherical diameter (ECD) as measured by the HIAC and Coulter counter for the samples investigates.A study of the image analysis data alone confirmed that OB and ECD were nearly identical with ECD running about 6.1 m̈m above OB.Mass resin samples, which are prone to electrostatic charging effects, tended to give slightly higher results in those methods which measured the resin in the dry state (HIAC and sieves). Finally, it should be suggested that many of the classical concepts of resolution and depth of focus which are used to place limits upon the performance of the optical microscope do not necessarily apply to particle size determination by image analysis. If the chord through the particle which describes its diameter can be considered an approximation to a square wave then it is the fundamental frequency of the Fourier components of that square wave that contains the size information. This should be true for microscopic objects which are absorbing of light and non‐retarding in nature.Once this fundamental frequency can be identified then sizing accuracy is dependent chiefly on the signal to noise ratio of t

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090114

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractLight scattering by moving particles as used in laser‐Doppler anemometry (LDA) is reviewed. This first part of the review describes the situation where the scattering particles play the role of tracers of fluid flow. In this situation only general properties of the scattering process are of relevance. No special knowledge of the specific scattering mechanism is needed, provided that a detectable signal intensity is obtained. The velocity of the particle in a direction determined by the two laser beams of an LDA measuring device can be derived exclusively from the modulationfrequencyof the signal. In the second part of the review a description of specific properties of the scattering process will be given with the purpose of gaining information on the particles themselve

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090115

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe turbulence occurring in the flow of the carrier fluid exerts a substantial influence on the motion of suspended particles or droplets. This influence is obvious, e.g. if fine particles are dispersed in free flows or deposited on free surfaces, bluff obstacles or channel walls. With application in aerosol science in mind, the interaction between dispersed phase and carrier fluid is described in terms of turbulence intensities, energy spectra, turbulence time scales and eddy diffusivities. Experimental results obtained for different important flow types are reviewed and compared with theoretical predictions. With regard to the latter, the different methods of treating theoretically turbulent two‐phase flows of low concentration are discusse

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090116

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe possibilities and limitations of photon correlation spectroscopy (PCS) as a practical tool for particle sizing are reviewed. In this part the most frequently used methods of data analysis are briefly surveyed. The practical performances for the determination of particle size distributions were evaluated by a comparative study with different kinds of users (industrial and academic research groups and manufacturers). The PCS results were also compared with electron microscopy (EM) and static light scattering (SLS) results. Thereby it was confirmed that the amount of reliable information that can be obtained by PCS about particle size distributions with measuring times of the order of minutes is limited by the ill‐conditioning of the data inversion procedure, among other factors. Nevertheless, the information obtained from the PCS measurements agrees essentially with the EM and SLS result

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090117

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractSince photon correlation spectroscopy (PCS) is essentially a light scattering technique, it estimates the intensity‐weighted particle size distribution. Using the Mie theory, some consequences were demonstrated. First, argon ion lasers were shown to be superior for particle sizing of very small particles. In addition, multiple scattering was shown to be largely dependent on the scattering angle and the state of polarization of the light source. Owing to this disturbing phenomenon, sizing of supermicron particles becomes troublesome. The estimated intensity distribution of polydisperse samples could be greatly influenced by the observation angle. The use of simplified light scattering theories such as the Rayleigh and the Debye‐Gans theory was shown to be limited to small particles, especially in the case of high refractive indices. Finally, it was shown that the smoothing effect of PCS data analysis software may give rise to artificial bimodal number‐ or weight distributions, even when the Mie theory is consi

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090118

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractBeam shape coefficients,g nm, are at the core of the generalized Lorenz‐Mie theory describing the scattering of a shaped beam by spheres. A decrease in computation times is essential for systematic applications of the theory. This paper introduces a new formulation to compute beam shape coefficients,g nm, in the framework of the localized approximation and discusses symmetry relations between the coefficients. The new formulation permits computation times to be decreased by one to two orders of magn

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090119

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractExperiments on the suspension polymerization of styrene were conducted at various stabilizer concentrations, dispersed phase hold‐up fractions, impeller types and impeller speeds. The experimental final particle size distributions obtained were almost always described by the upper limit number distribution. Plots of the maximum diameter,amax, and the mean diameters,a21anda10, vs. the Sauter mean diameter,a32, gave straight lines with slopes of 1.24, 0.99 and 0.97, respectivel

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090120

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

ISSN:0934-0866    

DOI:10.1002/ppsc.19920090121

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY