Particle diameter range, laser aerosol

Laser Doppler velocimetry has been combined with acoustic excitation to allow the derivation of the relaxation time for particles, from which the aerodynamic diameter can be calculated [132-136], The particle relaxation time is derived from the velocity amplitude of the aerosol particle and that of the medium while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure the velocity amplitude of the particle, and a microphone is used to measure the velocity amplitude of the medium. The aerodynamic diameter of the particle can be derived from the relaxation time and the known particle density. The method can be applied to real-time in situ measurement of the size distribution of an aerosol containing both solid and liquid droplets in the diameter range of 0.1 -10 pm. 

The particle size distribution of powders in the range 0.2-0.5 pm can be determined by automated electron probe microanalysis, as developed for particle characterization work at the University of Antwerp (see e.g. Ref. [202]). Here the exciting electron beam of a microprobe scans a deposit of the aerosol particles collected on a Nuclepore filter under computer control, and from the detection of element specific x-ray fluorescence signals, the diameters of a large number of particles are determined automatically. As shown by results for AI2O3, the particle size distributions determined by automated electron probe microanalysis agree to a first approximation with those of stray laser radiation (Fig. 62) [203], Deviations, however,... 

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