Abstract
In order to propose a formula of hindered settling velocity, the effect of concentration and size distribution of particles on the settling velocity of a particle in suspension was investigated by the experiment and computer simulation. In the experiment, the sedimentation behavior of particles which distributed uniformly in a rectangle container was observed using a high-speed camera at low particle concentration, and the settling velocity of a particle in suspension was obtained by analyzing the pictures. At high concentration, settling velocity of each particle cannot be observed visually with the high-speed camera. Then, particles were distributed uniformly in a cylindrical container and sedimentation velocity of interface between particles layer and fluid was observed. In the result, it was confirmed that as the particle concentration increased, the velocity of a particle decreased, the variation of each particle velocity became large, and the effect of the particle size distribution increased. The simulation was carried out to obtain the detailed data which cannot be obtained experimentally and is useful to propose an equation of settling velocity. On such a purpose, a direct numerical simulation (DNS) was used to calculate the fluid flow of the surface of a particle closely so that the effect of fluid flow on a particle behavior can be investigated, and a particle behavior was calculated by the discrete element method (DEM). Furthermore, we tried to develop the large-scale simulation using the earth simulator (ES) in order to represent more realistic simulation system because very many particles are needed to reproduce the particles with particle size distribution.
