摘要:

AbstractDescribing the disperse state is important for quality assurance, operational safety and the design and modelling of processes, especially in solids technology. Starting materials, intermediates and end products have to be characterized. Apart from representative sampling, preparation greatly influences the results of particle characterization. Very fine particles are normally agglomerated unless a highly dispersed state is stabilized by an additive. For a meaningful measurement, they must be preserved in this state or be definitely dispersed, depending on the type of problem.If the point of interest is the present disperse state with regard to the processing characteristics, e.g. for a filtration, the system should not be changed by the preparation method. If it is necessary to determine the property functions, i. e. the functional relationship between technological and physical properties, it is necessary in general to use a high dispersion energy or a long dispersing time in order to obtain the best achievable dispersion. The finer and more unstable a disperse phase is, the more the correct processing is important for the result. The problems of dispersion in gases and liquids are discussed with some examples.

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080102

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractRequirements for processes for air classification for the particle size ranged<5 μm are described. A classification principle and first experimental results are presented

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080103

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe dry deposition of particles from the atmosphere is not well understood for reasons of surface variabilities and mutual interactions between surface and particles. However, even relatively simple influences of physical parameters have so far resisted successful parameterization, although some progress has been achieved. There is no general way to determine the relative contributions of stochastic turbulent and Brownian diffusion and directed motions (i. e. sedimentation) to the total deposition velocity since they contribute in a nonlinear manner to the total deposition velocity. The directed motion is an unknown function of atmospheric turbulence, the particle diffusion coefficientDpand the sum of all directed particle motions by thermophoresis, diffusiophoresis, photophoresis, electrophoresis, sedimentation etc. Practically nothing is known about the action of the first three forces and even the easily accessible electrophoresis has not been considered relevant for deposition of atmospheric particles. Because it is relatively easy to change an electric field with all other parameters kept constant and measure the absolute difference in total deposition velocity the following experimental Laser‐Doppler study was intended to show the feasibility of the field‐changing‐technique and the magnitude of the effects without quantitatively determining the electrical mobility distribution as a function of particle

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080104

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractAn extended phase‐Doppler anemometry (PDA) system is described, which allows the user to measure the refractive index of spherical particles, in addition to their velocity, diameter and concentration. The extended PDA system incorporates two additional detectors on the receiving side. Each particle generates four Doppler signals. Phase shifts between two pairs of signals are recorded. The ratio between two measured values of phase shifts is a function of the particle refractive index. The phase ratio is shown to be fairly independent of particle velocity or diameter.Calculations based on Mie scattering theory demonstrated the feasibility of the concept. Measurements with monosize droplets of glycerine‐water mixture, covering the refractive index range 1.33–1.44, were used to verify the theoretical predictions. The instrument was also tested with spray flows.It is also shown how the phase‐Doppler technique may be used to distinguish between reflecting and refracting particles. This means that the extended phase‐Doppler system may be employed to recognize particle material, and also to measure locally particle velocities, sizes and concentrations, in a multiphase flow with several transparent dispersed phases and one dispersed phase consisting of reflecting

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080105

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractLaser‐induced and time‐resolved aerosol fluorescence is introduced as an analytical technique for the qualitative and quantitative determination of surface‐bound polycyclic aromatic hydrocarbons (PAHs). The analytical figures of merit are evaluated by studying the fluorescent properties (emission wavelengths and temporal behavior) of PAHs adsorbed on submicrometer NaCl particles. In addition to singly adsorbed PAHs on NaCl particles, a three‐component PAH adsorbate system is characterized. Detection limits are in the range 5 ng/m3(e. g. for anthan

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080106

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo techniques for on‐line particle size measurement are evaluated on the reproducibility of their volume distribution determinations. A forward scattering laser light devise is interfaced with a dilutor to examine the potential of this technique for high concentration streams. The forward scattering instruments are capable of outputting extremely reproducible distributions and here we show that when the dilutor is well designed, the on‐line instrument can have similar performance. We compare this with a scanning back scatter instrument which is directly inserted in highly concentrated slurries. We present the methods used to improve the robustness of the conversion of the output of the back scatter instrument to volume distributions. The output of the back scatter instrument is inherently less stable but with the proper methods one can obtain reproducibilities of the order of 2 to 6 perc

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080107

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThere are a limited number of phenomena occuring with aerosol particles that depend only on physical quantities. Examples of new developments in aerosol particle characterization in situ that make use of such phenomena are briefly reviewed. They concern electrophoretic size classification, inertial size analysis and shape characterization of agglomerates. In addition to deriving basic descriptors, measurements of composite quantities can be performed and developed into sensors. Examples of sensors responding to relevant complex aerosol quantities are explained.

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080108

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe response of optical particle counters to nonspherical particles is analyzed theoretically and on the basis of experimental results. Theoretical approximations valid for particle diametersd≪ λ andd≫ λ (where λ is the wavelength of light) are used to derive some general predictions about the influence of the particle shape on light scattering. These predictions are compared with experiments on six optical particle counters using nonspherical particles. The instruments differ in the kind of illumination (laser or incandescent light), the mean scattering angle and the receiver aperture. When the particle size is smaller than the wavelength the light‐scattering diameter of a nonspherical particle comes very close to its volume‐equivalent diameter. For irregularly shaped particles larger than the wavelength better conditions than giving a “projected area” response cannot be achieved with an optical arrangement for single‐pa

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080109

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractCrystals and crystal agglomerates exhibit a number of specific shape features which evolve in close relation to the conditions of growth and agglomeration. Hence the quantitative evaluation of these shape features by adequately defined shape parameters can serve to obtain a deeper insight into the mechanisms and kinetics of crystal agglomerate formation and to quantify more precisely the quality of crystallization products.

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080110

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractBased on physical assumptions, simple equations have been derived for the probability of breakage of particles, for the dependence of fragmentation energy on particle size and for the fragment size distributions as a function of mass‐specific energy. The particles were considered as spheres, and Hertz theory of the stress distribution at the contact between a sphere of brittle material and a flat surface was applied in combination with Weibull statistics of failure. The predicted dependence of the probability of breakage on particle size and mass‐specific energy agrees well with experimentally obtained data for single‐particle experiments, even if the particles were not spherical. The resulting fragment size distribution could be predicted by the application of fracture mechanics. The theory can also be applied to rock drilling, where the breaking material is considered as a flat surface and the drilling tool as being of spherical shape. In both comminution and drilling, the experimental results agree fairly well with the t

ISSN:0934-0866    

DOI:10.1002/ppsc.19910080111

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY