The optical method is of advantage in measuring particle size instantaneously and automatically, and the diffraction method is more sensitive to the particle configuration than the scatterring method.
A measuring apparatus using the diffraction method is constructed which has a simple structure to improve its reliability and has a circular aperture behind the sample cell to allow easy adjustment. It is easy to take in data at a high sampling rate because of the use of an electronic sampling method without mechanically moving parts, and the data aquisition is also carried out at high speed. But it is not necessary to display the size distribution, mean diameter and variance as fast as in sampling. The data are mostly processed with a microcomputer.
Using this apparatus, the measurement of particle size is carried out for spherical and aspherical samples. Furthermore, the measuring range of particle size is extended reasonably to some extent by means of simutaneously processing two independent signals of each particle which are proportional to the square of diameter.

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Fundamental experiments have been conducted to clarify the effects of air humidity on the performance of a fabric filter. Three kinds of test dusts (calcium carbonate, Kanto-loam JIS No. 8, and fly ash JIS No. 5) are used.
Particle size suspended in air by a mixer type disperser becomes coarser, as the relative humidity increasses, because of particle agglomeration. However, the humidity of air does not have much effect on the pressure loss and particle penetration. This is true especially when the agglomerated particle size distributions of the airborne dusts are controlled so as to be almost constant in spite of the humidity of air.

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The pressure drop characteristics through a solid-particles moving bed using mechanical agitators are influenced by various factors such as the physical properties of the solid particles, the agitator geometry and the operating conditions. The present paper describes the results of an experiment on the relationship beween the pressure drop and the factors in the moving bed with solid-air counter-current flow. The bed is operated at an air velocity less than minimum fluidization velocity u_mf. A double herical ribbon is employed as an impeller.
The decrease in pressure drop with increase in the void fraction due to solids moving downward and agitation has been measured by using pressure sensing sets along the column height.
A general correlating equation for the pressure drop of the solid-gas moving bed has been provided in terms of the pitch ratio of the impeller, its width ratio its spacing distance and the gas flow rate and the rotary speed of the impeller.

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Size classification of submicron particles has been carried out by use of a small cyclone, the diameter of which is about 100mm∅. JIS Kanto loam powders are successfully classified at about 0.5μm. cut sizes. However, calcium carbonate has some difficulties because of its strong cohesion force. Fine silica sand and JIS flyash, the undersizes of which are less than a few percentages at 1μm, cannot be classified because of bouncing and re-entrainment of coarse particles and of the adhesion of fine particles to coarse ones in cyclone.
Precise size measurements of submicron particles are very difficult using present instruments. It is neccessary to develop more reliable measuring methods than the present techniques in order to obtain accurate partial separation efficiencies in the submicron size range.

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Entropy is proposed as a quantity measuring the randomness of the packing structure of granular materials. The entropy of the particle size distribution is considered, which makes clear the relationship between present entropy and those in information theory, statistical mechanics and thermodynamics. It is shown that there are problems in similar types of existing theories and it is concluded that the entropy represents a “distance” between an observed distribution and a reference distribution. The entropy of the void fraction distribution is considered as an illustrative example.

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