Hideo Nakakura

Dependency of tortuosity on capillary suction potentials of compressible and incompressible particulate beds

Measurements of capillary suction potential in drainage processes have developed a capillary bundle model, which makes it reasonably possible to deduce a dimensionless capillary suction potential by considering the dependency of tortuosity. The capillary suction potential has been found to depend strongly on the tortuosity, especially for the compressible filtered cakes. The tortuosity determined empirically using the capillary model provides the dimensionless capillary suction potential which can correlate to the reduced saturation for both incompressible particulate beds and compressible filtered cakes. The final average residual saturation can be accurately estimated from calculation of a newly defined capillary number, which takes into account the final equilibrium saturation profile. The calculated results agree well with experiments observed for incompressible particulate beds drained under gravity.

Centrifugal Permeation Process of Fluid Through Solid Particle Deposit.

Centrifugal permeation process of fluid through solid particle deposit was analysed theoretically. In accordance with this analysis, it was shown that the centrifugal permeation process was able to be predicted by the aid of the compression permeability data. The predicted centrifugal permeation processes were favourably consistent with the experimental processes for limestone-, coal- and yeast-water slurries.The specific flow resistance of particle deposit depends in general on hydraulic pressure, but that of the centrifugal process is able to take different value even under the same hydraulic pressure due to its thickness. For predicting the specific resistance of the centrifugal permeation, it is accordingly essential to take into account both of the hydraulic pressure and the solid compressive pressure distribution in the deposit differed with each thickness. When the specific resistance of filtration or permeation process under pressure or vacuum has to be examined and utilized cocurrently with that of centrifugal to design and scale-up the process, it was shown that the average compressive pressure defined in this paper was effective as the pressure variable.

Deashing of coal by selective flocculation using heavy oil.

高濃度脱灰炭-水スラリ-製造を目的に, 凝集剤として重油を用いた場合の微粉炭の選択凝集性について実験的に検討した.この方法において, 石炭-水スラリーは分散剤としてのトリポリ燐酸ソーダ添加下で調整された.次いで炭質分は選択凝集された後, 高速撹拌下で生成した微細気泡とともに浮上された.凝集浮上物はフロック中に混入した灰分を除去するために水で洗浄された.脱灰特性に影響する操作因子, すなわち撹拌時間と回転数, 分散剤添加量, 油の添加量, 洗浄条件および石炭粒子径等の影響について調べた.その結果, 最終灰分量を大幅に減少させるためには, 撹拌による灰分の洗い出しが不可欠であることが分かった.最適操作条件下で, 三種の瀝青炭について石炭を95wt%通過約30μm以下に粉砕すれば, 炭質分回収率98%以上で灰分量15%以下の脱灰炭が得られた.

Effects of film flow on gravitational drainage of highly viscous fluids.

A method is presented for calculating the drained liquid volume in gravitational drainage by applying an empirical correction, which takes into account the effects of liquid viscosity on film flow, to the authors prior equations for the dewatering of granular beds. It was shown that the dehydration rate of highly viscous Newtonian liquid is strongly affected by the existence of filmwise liquid flow when the modified capillary number is larger than 2.5.The predicted results agreed well with the experimental results for packed beds of glass beads and calcium carbonate particles of diameter 1641875 μm, under conditions where the liquid viscosity ranges from 0.001 to 0.76 Pa · s.

Assessment of dispersibility of coal particles by the sedimentation method using hydrometer.

The dispersion effect consequent upon the addition of surfactants to coal particles in water was examined by means of the sedimentation method using a hydrometer to obtain fundamental information on preparation of a highly loaded coal-water mixture. This method was found to be useful for assessing the settling characteristics of coal particles in a dilute suspension.