The effect of surface modification on powder flowability was experimentally investigated in the present study. The powder sample was granulated lactose with 147 ‍μm mass median diameter, which is used as an excipient for direct compression. The surface of the granulated lactose was modified by mechanical dry coating with silicon compound glidants, namely magnesium aluminometasilicate, aluminum silicate, magnesium silicate, and silicon dioxide, which were 3 to 13 ‍μm in mass median diameter. Powder flowability was evaluated by a vibrating tube method, which can characterize both the static and dynamic friction properties, and by conventional methods, i.e., measuring the angle of repose and compressibility. Finally, effective surface modification agents that improve powder flowability were selected from the tested silicon compounds.

A new method for evaluating powder flowability is developed using a constant volume shear tester; this tester measures the upper and lower normal stresses and the shear stress acting on a powder bed. A single shear test provides a series of characteristics, such as powder yield locus (PYL), consolidation yield locus (CYL), critical state line (CSL), shear cohesion, stress relaxation ratio, stress transmission ratio, and void fraction. The values of the shear stress as a function of the normal stress and the void fraction are visualized in three-dimensional diagrams. Furthermore, powder flowability is evaluated using a flow function obtained from the PYL.

Four pairs of binary mixtures of glass beads and iron powder were fluidized at various air velocities. The size of iron powder was constant at 180–212 ‍μm, while that of glass beads was varied to be 250–300 ‍μm, 300–355 ‍μm, 425–500 ‍μm and 610–700 ‍μm. It was found, in the four pairs, that glass beads (lighter particles, flotsam) move up and iron powder (heavier particles, jetsam) move down at middle ranged air velocities; density segregation appears regardless of the glass beads size. However, if the lower iron-powder-rich layers were investigated carefully for the pairs of 250–300 ‍μm and 300–355 ‍μm glass beads, the volume fraction of iron powder decreases with lowering the bed height, that is, the glass beads are captured in the lowest layer. On the other hand, the capturing of the glass beads does not occur in the pairs of 425–500 and 610–700 ‍μm glass beads. The origin of the glass beads capturing, and the reason of the presence or absence at different glass beads sizes were discussed considering the particles mobility at the interface between upper and lower layers, the particles packing structure of the lower layers, and the local air velocity at the lower layers.

Grinding is one of the most basic and important operations of powder processing. Grinding has been carried out all over the world for a long time. However, the grinding mechanism has not been elucidated scientifically. Computer simulation have a possibility to be a useful tool to clarify the grinding mechanism. In this review, new simulation methods for particle breakage were introduced, and the advantage of each method was discussed. Prediction of grinding results based on the impact energy has an advantage of calculation load, however, it is difficult to analyze the grinding process. On the other hand, direct simulation of particle breakage can analyze the grinding process. It is necessary to choose an appropriate method according to the purpose.

A method for analyzing quantitatively the effects of particle shape and size distribution on the size segregation of particles using DEM simulation, which employ spherical particles with an equivalent friction coefficient to efficiently incorporate the effect of particle shape was proposed. In order to quantitatively evaluate the particle size segregation occurring during gravity filling of a container, two metrics were used: a segregation index and the percolation index.

Moreover it was indicated that a combined CFD/DEM approach was required to apply this method to a design of a high–speed suction filling process of fine powder.

In a number of applications of dense gas-solid flows such as fluidized bed and pneumatic conveyer, the size of solid particles is not uniform and a large size difference exists. Because it is strongly related to the system efficiency, the understanding of mixing and dispersion characteristics of the particles in detail is important while it is not trivial due to inherent complexities of phenomena and measurement difficulties in experiments. In this review paper, fundamentals and results of several validation studies of Fictitious particle method (FPM) that is a model extended from Discrete element method-computational fluid dynamics (DEM-CFD) targeting systems with large particle size difference are presented.

Numerical simulation techniques concerning pulverized coal combustion and gasification have been continuously developed and applied to a wide range of reactor scales. Very recently, unsteady large-scale simulations become to be paid attention to with the computer hardware development. This paper describes the recent development of the unsteady large-scale simulations of pulverized coal combustion and gasification on the demonstration-scale reactors by means of large-eddy simulation (LES). In addition, recent sub model developments for coal combustion and gasification are also reviewed and assessed in terms of the model accuracy.