A relationship between the fluid flow velocity u[m/s] and the hydraulic gradient Δh/L [-] in a granular bed was proposed by Izbash as follows; u=M(Δh/L)ⁿ, where M and n are the constants to be determined by the flow and medium properties. According to Soni, Izbash's equation is completely empirical and has not yet been given any theoretical basis by any investigator.
In this paper, an attempt to explain the theoretical basis of Izbash's equation, based on the drag model of particles, is given. The value of n is given as a function of the particle Reynolds number over a wide range of flow regimes by use of the correlation between the drag cofficient and the particle Reynolds number. Also a dimensionless equation is developed without regard to n. The calculated velues obtained from the drag model taking the suitable correlations of the drag coefficient and voidage function into account are in good agreement with the experimental correlations proposed by Kozeny-Carman, Burke-Plummer, Ergun, Chilton-Colburn, and Rose. These facts show the validity of the drag model.

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A method is desbribed for evaluating the flowability of cohesive powders on the basis of their yield loci. The measured yield loci are represented by the Warren Sqring equation that is defined by the three parameters K (the ratio of cohesion to tension), n (the shear index) and δ' (the slope of the straight line joining the end point of the yield locus to the origin). One of important properties of a cohesive powder is the unconfined yield stress f which is defined by the two parameters K and n. The unconfined yield stress varies with the major consolidating stress σ₁ defined by the three parameters K, n and. δ′ The ratio σ₁/f called the “failure function” by Jenike, however is not commonly a fixed value for the cohesive powder.
In this work the flowability of the cohesive powder is expressed by the ratio of the unconfined yield stress f to the corresponding bulk density γ. This flowability means the maximum height that the powder layer having an unit cross-sectional area is able to stand vertically under the force of gravity only. The value of f/γ varies with the major consolidating stress σ₁, and an empirical equation of f/γ=aσ₁^b is confirmed for 13 kinds of cohesive powders used over the range of σ₁ less than 100kP_a. The two coefficients a and b are characteristics representing the index of flowability for the cohesive powder.

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Recently, the development of dust collecting equipment which is suitable for high temperature, corrosive and combustible gases has been anticipated. For this purpose, it is said that a packed granular bed is one of the most suitable pieces of equipment. In this report, the fundamental properties of a fixed bed dust collector were experimentally mirstigated and a few theoretical formulas to extend the applicability of the system were presented.
The following results were obtained:
1) The dust collecting mechanism in this type equipment is divided into two parts, dust filtration at the surface of the bed and filtration inside the packed bed itself (so called “depth filtration”). In our experiment, the latter action is much more effective than the former. A micro-silica particle was used for the dust, and oil coke granules (2-5mm∅) were used as the dust collecting (packing) medium.
2) For the depth filtration effect described above, the existence of the optimal gas velocity was found This velocity is almost indifferent to the size of the medium in the range of this experiment.

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Using ethyl p-hydroxybenzoate (Et-POB), methyl p-hydroxybenzoate (Me-POB) and lactose, the effect of temperature on the tensile strength as well as the surface area was examined.
For Et-POB and Me-POB, it was found that the tensile strength (σ) increased and surface area (S_w) decreased with an increase in heating time. These results can be explained in terms of the sintering mechanism.
The tensile strength for both powders showed maxima between a homologous temperature of 0.9 and 0.95. This observation suggests that the packing structure of a powder bed alters at temperatures closer to their melting point; that is, agglomerates may be formed by a marked increase in the adhesive force between particles.
There is an approximately linear relationship between the reduction in surface area (ΔS_w) and the tensile strength (σ). This may be attributed to the fact that the increase in tensile strength is due to the increase in contact area between particles which is proportional to ΔS_w.
For lactose, the results were complicated by the evolution of water of crystallization at above about 120°C, although the results in the lower temperature region are almost identical to those of Et-POB or Me-POB.

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Using a “Coke-Tester” which is a sophisticated split-cell type tensile strength tester, a new method for measuring the yield locus of a low stress region of a loosly packed cohesive powder is proposed.
The movable cell is pulled horizontally while in the vertical direction a compressive stress is applied by weights placed on the surface of the sample powder. Failure of the powder bed commences when the state of stress in the bed reaches the plastic equilibrium. If the vertical compressive stress coincides with the major principal stress σ₁, the measured tensile strength indicates the minor principal stress σ₃, and therefore a Mohr failure circle is obtained for each measurement. By drawing an envelop around Mohr's failure circles obtained for several values of σ₁, PYL is determined corresponding to the specified porosity of the bed. This method is also useful for evaluating the unconfined yield strength of the powder bed.

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The correlation between initial bulk density and flow-patterns were investigated using a model bin. A two-dimensional rectangular bin (10cm×5cm×40cm) was filled with Toyourasand, having a particle size of 105-297μ.
The following results were found from the experiments:
(1) The bulk density leads to the Mass-Flow type when loosely packed, and the funnel-flow type when closely packed
(2) When the Mass-Flow type is transformed into the Funnel-Flow type, there is a linear relationship between the initial void ratio of a model bin and the rate of the flow region, which means the ratio of the width of the main (sub)-flowing region and the width of a model bin.
(3) When the Mass-Flow type is transformed into the Funnel-Flow type, the differnce between the maximum and the minimum bulk density in the vertical direction of the same model has a maximum value.

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