Distinct element method (DEM) requires enormous computation time because it needs small time increments that are sufficient to follow high frequency fluctuations in contact dynamic model. In general, the equations of motion of particles are solved by the second order Adams-Bashforth method, which estimates the contact force for the next time step by linear extrapolation, or by multistep methods such as predictor-corrector method. In order to overcome the deficit of conventional methods, we propose a Contact Force Prediction Method that allows us to use larger time increments. The method incorporates the contact force at every contact point obtained as the exact solutions or numerical solutions of differential equations that describe two particle contacts. It is confirmed that the proposed method gives the simulation results for packing and discharge of particles which are consistent with the experimental data, while accelerating DEM computation by 3 to 8 times.

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Segregation and dynamic behavior of air bubbles and binary particles in 2-D gas-solid fluidized beds were investigated by recording video movies of fluidization, rising air bubbles and the movement of a plastic disk immersed in the fluidized beds. Four types of binary particles of different sized glass beads were employed. Segregation occurred in all four cases; flotsam and jetsam almost completely separated into upper and lower layers. When binary particles with large particle size diffrences were employed, the boundary surface between the flotsam and jetsam layers swelled near the side-walls and air bubbles generated frequently at the swell. In the upper layer of flotsam, particles rose up at the center of the column and fell down near the side-walls. However, at the lower layer of the flotsam, particles rose up near the side-walls and fell at the center. These results indicate that complicated particle flow can occur in fluidized bed of binary particles, which is dependent on the shape of boundary surface between the flotsam and jetsam layers.

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