Errors in anisokinetic sampling for aerosol concentration measurements are affected by the shapes, wall thickness of the nozzles and size distribution of particles. Moreover, it is expected that the particle concentration distribution in the nozzle is not uniform. The numerical analysis were carried out to obtain the flow field around the nozzle using the finite element method in a potential fluid, and particle motion with the Runge-Kutta-Gill method. For superisokinetic sampling (V_o/V_s<1), the shape and thickness of nozzles had little affect on the sampling efficiency, whereas the effect was significant for subisokinetic sampling (V_o/V_s>1). The analytical results of the sampling efficiencies agreed fairly well with the experimental data for a Stokes number of Sk_(D)<0.5. The calculated particle concentration distribution showed a maximum at a dimensionless radial distance of around 0.7 for superisokinetic sampling, while it flctuated markedly near the nozzle axis for subisokinetic sampling.

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The alumina particles were ground with an annular type beads mill, and the effect of dispersing agent (sodium hexametaphosphate, abbre. S. H.) on the grinding process and the particle size measurement were examined. The following results were obtained: (1) Almost the same 50% particle size change with the grinding time was obtained regardless of the initial S. H, conc. in grinding when 3mol/m³ conc. at S. H. solution was used as a dispersing medium for particle size measurement: (2) Reversed grinding(that is, flocculation) apparently occurred at the lower initial S. H. conc. in grinding using pure water as the dispersing medium: (3) The existence of S. H. gave the lower specific surface area measured by the B. E. T. method: and (4) The X-ray diffraction analysis showed that other crystalloid materials were not formed with the existence of S. H. although the ground particles become partially amorphous.

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Fine particle classification by probability through apertures in a wet process was investigated. In this method, the probability of passage through an opening is a function of the ratio of a particle size to an opening. The recovery of particles was measured with variations in particle concentration, particle size, and opening. The experimental results agree well with the calculated values. Therefore, a multistage process of classification even with full pass screens with result in a narrow particle size distribution. This method is applicable for the mass production of fine particles in a wet process.

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The flow characteristics of pneumatic conveying containing unstable flow regions were studied by making use of nearly practical scale pipelines in abroad air velocity range of approximately 1-20m/s.
The variations in the pressure in the tank and pipe, and the conveying flow pattern and conveying efficiency are intimately related to each other. A conveying state is classified into three regions: the suspension, plug conveying regions and the unstable one between those regions. In the unstable region, the flow pattern of plug conveying and suspension after blowing off the plugs are mutually generated.

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