ISSN:0934-0866    

DOI:10.1002/ppsc.19960130102

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractA novel technique to determine the size of particles suspended in a stirred vessel is investigated. The method uses microphotography to obtain a still image of the particles in situ. The equivalent circular diameter of the particles is obtained from the photographs using digital image analysis. The particles used for the test were certified particle size standards of a very small tolerance in diameter deviation. The size comparison was determined as a percent error between the measured particle diameter (equivalent circular diameter) and the diameter established by the particle manufacturer. To determine the limiting ranges of particle size and concentrations, spherical particles in a size range of approximately 1 to 10.0 μm (microns) in diameter were employed in the test. Concentrations varied from 0.00005% to 0.1% (mass basis). For each particle size, an aqueous solution of the particles was prepared at the desired concentration and placed in a stirred vessel. Photographs of the solutions were made at 25.5x, 40x, 60x and 80x magnification. For all sizes of particles, the entire range of concentration was examined.The results indicate a minimum size resolution of approximately 3μm, in a corresponding concentration range of 0.0001% to 0.05%. Similar limits on concentration were found for the larger diameter particles, although a true upper limit for the largest particle sizes was not established. The functional concentration range appears to shift towards higher mass concentrations with increasing particle size. For 2.92 μm diameter particles, the error in size measurement was found to be below 10% for a concentration range of 0.0005% to 0.05%. Additionally, a relationship between turbidity and the error was seen at low particle concentration levels where decreasing levels of turbidity generated increasing levels of err

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130103

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe particle size distribution of crystalline solids has progressively become a key parameter in manufacturing processes, as important as chemical purity. Among the particle size determination and counting systems available on the market, very few offer the possibility of continuous in situ monitoring of the particle size evolution during crystallization. For this reason, much interest has been aroused by the appearance of the Par Tec 100, patented by Laser Sensor Technology [1, 2]. A study has been carried out in a stirred vessel to verify the precision and reproducibility of particle size measurement and elucidate the influence of experimental parameters on data accessible with this instrument. Optimum reproducibility has logically been achieved by fixing the highest possible cycle time and taking the mean of several cycles. Determinations with the Par Tec 100 are influenced variously, according to whether they relate to the total number of particles counted or to the mean size. Thus, the number of counts measured by a particle size probe largely depends on the operating conditions and more particularly on the hydrodynamic conditions, solvent, temperature and focal point position. Its dependence relative to the concentration of the solid in suspension is normal and linear for a solid and for a given monodisperse sample. To establish the relationship between the number of counts and the population density would therefore necessitate delicate calibration on a case‐by‐case basis. The mean size determined does not depend on suspension homogeneity, provided that the stirring speed is sufficient for a statistically significant total count. On the other hand, for a given sample, a displacement of the focal point can lead to considerable variations in the size determined. The optimal focal point position for small sizes is in fact highly sensitive. Lastly, the optimal position of the focal point is considerably dependent on the true size of the particles, which means that this counter is unsuitable for the precise analysis of a dispersed sample since each particle size class would require a different setting of the focal point. In addition, the sizes determined, irrespective of the products studied, appear to be underestimated for large particles and over estimated for small partic

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130104

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe influence of the measurement volume can be investigated by using extended geometrical optics, which is based on geometrical optics by including the amplitude and phase distribution in the laser beam. The dynamics in phase Doppler anemometry can be analysed, in addition to effects of the particle size‐dependent detection volume. Extended geometrical optics has been developed as a powerful tool to investigate these influences for each order of light scattering separately. Phase errors caused by Gaussian‐beam intensity distribution and the curvature of the wave fronts beyond the beam waist can easily be calculated. According to Part 1 (Reflective Mode Operation), the influence of the particle trajectories on measured phase and mass concentration is simulated for refractive mode operat

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130105

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractA new phase Doppler anemometry (PDA) signal processing method based on a Hilbert transform algorithm is introduced and analysed. By generating a 90° phase‐shifted burst signal in the time domain, the envelope of the Doppler burst can be determined. In addition, this envelope is approximated by a Gaussian exponential function. The difference of the maxima of these Gaussian approximations for two related PDA bursts gives an estimate of the time difference between these time shifted signals. With the introduction of this estimation method, the restriction to the [0,360°] interval resulting from conventional signal analysis may be avoided in many cases. To investigate the dependence on SNR, burst position, burst frequency and sampling rate, results of computer simulations are presented. The feasibility of the method is demonstrated briefly by experimental results. Phase differences of more than 2000° arising from the measurement of monodisperse droplets by a conventional PDA setup could be determ

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130106

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractMicrocontamination of product surfaces by deposited particles is an important problem in clean technologies. A most sensitive product to contamination by particles is a wafer during chip production. Therefore, methods for monitoring particle deposition on wafer surfaces have been developed in the last decade. A wafer with an unstructured and reflecting surface is inserted into the process equipment. After some time, depending on the process, this wafer is removed from the process equipment and is analysed with respect to the number of deposited particles using a wafer scanner. However, in situ particle detection in a process chamber is not possible with this technique. This would be possible if, instead of a monitor wafer, a transparent glass plate is mounted, e.g. in the housing of the process equipment. Then the illuminating and scattered light detection equipment can be mounted outside the process equipment. Since both the illuminating laser beam and the scattered light have to be transmitted through the glass plate, losses will occur, which will reduce the lower limit of detection with respect to particle size. In this article we estimate the detection possibilities theoretically and experimentally.A simple model based on Mie and vector scattering theory has been developed to describe the light‐scattering behavior of a single spherical particle on a glass plate with random surface irregularities. The scattered light of individual particles of four particle sizes (1.03, 1.6, 2.92 and 4.23 μm) on the same glass surface and from the uncontaminated area of the glass plate was measured for unpolarized and normally incident light. The values of the scattered light from this model were compared with the experimental results. The comparison shows a reasonable agreement of the angular distribution of the scattered light. The developed model is used to predict the lower limit of detection for particles on a transparent surface. The theoretical estimations show that it should be possible to detect particles of a diameter down to 0.2 μm with the described measurement techni

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130107

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, particles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate into large particles or are deposited on the walls. Particles larger than 4nm and molecular clusters penetrate through a wire‐screen type diffusion battery, but particles in the size range between 2 and 4nm are collected. Among the organic compounds tested (aromatics, alcohols, ketones and others), only aromatic compounds appear to yield unstable clusters which grow into detectable particles (>2nm) through Brownian coagulation. The other compounds either do not undergo the gas‐to‐particle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle form

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130108

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractElectrically active fibrous filters, that is fibrous filters whose fibres carry a permanent electric charge, are an increasingly popular alternative to conventional fibrous filters in applications where low pressure drop and high collection efficiencies are critical. The advantage of these materials is the additional collection efficiency, due to electrostatic mechanisms, that can be achieved without pressure drop increase. The efficiency of these materials can fall as they are loaded with aerosol particles, so it is necessary that proper account be taken of this process during use. A complete understanding of the mechanisms responsible for this reduction in efficiency has not yet been reached. An experimental study has been undertaken at Loughborough University of Technology investigating the loading behaviour of a mixed fibre type electrically active material. The experimental techniques used in this work and experimental findings with a range of aerosol particle sizes are reported here.

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130109

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130110

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0934-0866    

DOI:10.1002/ppsc.19960130101

出版商:WILEY‐VCH Verlag GmbH    

年代:1996

数据来源: WILEY