In order to estimate the main hopper side slope in the cargo holds of self-unloading ships, a triangular, rigid, powder block was assumed at the transition of the walls of the cargo hold. When a given size of the powder block just slid off the hopper walls, the critical hopper slope was calculated from the force balance on the powder block.
The calculated critical hopper slope increased with a decrease in the size of the powder block, and a maximum value was obtained when the powder block became infinitely small. For the desigh of the cargo hold, this maximum value was taken as a lower bound of the main hopper side slope.
When assuming that the cargo hold is for carrying coal, the calculated hopper slope was 40°against an ulrta high molecular weight polyethylene plate, and was 51°against a steel plate. These calculated results were slightly large in comparison with the main hopper side slope adopted in the cargo holds of existing self-unloading ships. Consequenty, a low hopper slope required both a low frictional coefficient and a low adhesive force between the powder and the wall material of the hopper.

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The characteristics of a cascade impactor have been studied for specific conditions. It is clearly shown that the standard deviation of measured particle size distribution becomes larger than the true value when nearly mono-dispersed particles are measured. It is found that the experimental maximun flow rate is a few percent lower than the theoretical value because of the boundary layer in the nozzle region. The effects of temperature and pressure upon the cut size of an impactor are also studied, showing that the cut size becomes greater as the temperature increases and smaller as the temperature and pressure decrease.

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