The authors did research on the effect of the Reynolds number on the permeability coefficient of a porous media, and the effect of flow velocity was especially examined.
In the case of a low Reynolds number, limited Reynolds numbers exist and they were changed by particle diameter and apparent density.
In the case of a high Reyonlds number, the permeability coefficient rapidly decreases with increasing flow velocity.

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Single particle crushing of glass beads, under impact loading, classified into five ranges of grain size was carried out with a drop weight-type impact loading apparatus. The fragment size distributions of the fractured product and the fatigue fracture were investigated using size analysis with standard sieves. The experimental results are summarized as follows: 1) The relationship between the fracture probability (p_f) and impact energy of drop weight (E) is expressed by the following equation; P_f=1-exp{-(E/E₀)^1.5}, where E₀ is a referential impact energy; 2) The amount of increase in the specific surface area of the fractured product (ΔS_f) is proportional to 0.7 power of the impact energy of drop weight, regardless of the size of particle, mass and kind of drop weight; 3) The residual probability of particle (1-P_f) decreases exponentially with the number of the repeating impact load (N) as in the following equation; (1-P_f)=exp(-cN), where c is a function of the impact energy of the drop weight per unit mass of particle; 4) Particles easily fractured under small impact energy produce finer fragments compared with particles of high fracture strength.

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An experimental study on the production of fine powders was carried out by an agitating mill devised to produce ultra-fine powders by the mutual friction of sample powders of gypsum. The following results were obtained:
(1) Powders of micron order could definitely be produced by this method and there was only a few percent of submicron powders produced, but it was proved that the production of ultra-fine powders was possible by this method.
(2) The size distribution curves of the produced powders shifted toward smaller particle size with grinding time and the rotating velocity.
(3) The relationship between the specific surface area produced and grinding energy conformed to the final finness limit theory proposed by T. Tanaka.
(4) The specific surface area produced increased with the rotating velocity of the impeller and finally approached a constant value.
(5) When the rotating velocity of the impeller was under 3620 1/min, the specific surface area produced was scarcely affected by the mass of fed sample powders, but at over 4800 1/min it increased as the mass increased.
(6) The specific surface area produced increased with the ratio of the fed sample volume to the agitating vessel volume and finally approached a constant value.
(7) The relationship between the specific surface area produced and various factors was obtained by dimensional analysis.

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Slurries composed of water, binders and roseki, which is a kind of clayey particles having a particle size less than 10μm, have been atomized and dried in a spray dryer with pneumatic atomizers to examine the influence of operating variables and the properties of slurries on the mass median diameter and size distribution of spray-dried particles. The strength of single spray-dried particles obtained under various experimental conditions has also been studied experimentally and theoretically.
The conclusions obtained are summarized as follows. The mass median diameter of spray-dried particles was found to be estimated by both Kim-Marshall's equation and a mass balance on the solids in a slurry droplet and a dry particle. However the apparent viscosity of slurries at the shear rate of 300s^-1 was used in calculating the Kim-Marshall's equation. The size distribution of the dry particles approximated to the logarithmic normal distribution and the geometric standard deviation, one of the parameters in the distribution, could be expressed by using the mass and number median diameters, respectively.
A theoretical equation was moreover derived on the crushing strength of single spray-dried particles and was found to show a good correlation with observed values. The crushing strength of the single dry particles was also observed to be nearly equal to the constant, 1/b, in Kawakita's equation, which was obtained from packing or compression experiments on dry particles.

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A general mathematical model for predicting the drug release from various shapes of matrix-type drug delivery systems was solved using a method-of-lines procedure. The effects of the device shape, the diffusion boundary layer and the internal structure (porosity) on the rate of drug release were analyzed numerically. The present study is of practical significance for establishing an optimum design method for matrix-type drug delivery systems.

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