A partition plate and/or a circular cone has been inserted into a circular hopper in order to reduce the static compressive stresses exerted by a bulk solid. The circular cross section of the hopper has been vertically divided into four, crosswise by means of a partition plate. The circular cone has been laid at the centre of the top of the partition plate. Experimental results show that the vertical stress measured when filled with a bulk solid could be conspicuously reduced by the partition plate and/or the circular cone.
A method for estimating the static stresses has been obtained from a force balance on a differential volume of the bulk solid on the assumption that the vertical stress was uniform over the cross section of the hopper.
Calculated vertical stresses are in sufficient agreement with measured values for both the hopper alone and that equipped with the partition plate. For the hopper equipped with both the partition plate and the circular cone, the cone has functioned to reduce the vertical surcharge stress at the level of the cone bottom. A coefficient for estimating the effect of the cone, the values of which were determined from comparison between the measured and calculated vertical stresses, has been shown to be dependent of the diameter of the circular cone.
A further purpose of this work is to prevent a stable arch above the hopper opening and to ensure gravity flow of the bulk solid.

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Separation performance of several small cyclones have been studied experimentally. A cyclone, the diameter of which is about 100mm, can separate submicron particles, because there are less than 10% of particles above 1μm in the downstream flow of the cyclone. A cyclone, the diameter of which is less than 100m, is not useful because there is no further improvement in the separation performance by the reduced diameter, and the clogging of the dust discharge is more liable to occur. A German type cyclone, which has an inverted cone in the dust chamber, also performs well.

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An experimental study was carried out in which an efflux tube is attached vertically to the efflux orifice of a hopper, and the flow rate of powders flowing out of the tube and the pressure in a tube are controlled. The air from a compressor is blown into the tube, and its position is fixed directly below the orifice. As samples, mixed powders, i. e., the same kinds of powders having different particle diameters (glass beads), different kinds of powders having the same particle diameters (glass beads and styrol resin) and additives of a flow-improving agent, talc to glass beads are used. A flow rate of powders and the pressure distribution in a tube are measured for various combinations with volumetric flow rates of air and mixing ratios of powders or additive rates of talc.
It was found that a flow rate decreases if the volumetric flow rate of air increases, and their relationships become nearly a straight line both in the uniform down-flow state and in the discontinuous state for all samples and when tho gradients of those straight lines are affected by the mixing ratios and the additive rate of talc. The curve shapes of the pressure distribution differ with the volumetric flow rate of air, and its minimum values exist. The positions of these minimum values shift upward if the volumetric flow rate of air increases and differ with the kinds as well as with the mixing ratios of the powders and the additive rate of talc.

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