Reverse to Forward Density Segregation Depending on Gas Inflow Velocity in Vibrated Fluidized Beds

Zhaohua Jiang, Takuya Tsuji, Jun Oshitani, Kimiaki Washino, Toshitsugu Tanaka

Particle density segregations in vibrated fluidized beds depending on gas inflow velocity under the same vertical vibration condition are
studied. Coarse-graining discrete element method and computational fluid dynamics numerical simulations are employed to capture the
behaviors of reverse segregation in which heavy particles are located above light particles at zero gas inflow velocity or at velocities considerably
lower than the minimum fluidization velocity of light particles. Furthermore, upon increasing the gas inflow velocity slightly, the forward
segregation occurs, such that heavy particles are located below light particles. The mechanisms are also elucidated using the simulation
results. Because of the relative motions between the particles and bed caused by vertical vibration, negative gauge pressure is observed to be
dependent on the vibration phase. In the reverse segregation case, the accumulative effect of the downward gas pressure gradient force
induced by vibration overcomes the upward force of the forced air flow. The wall friction transports both the heavy and light particles in the
vicinity of the sidewall to the bed bottom, where the local void fraction is comparatively high and reverse segregation mainly occurs. Reverse
segregation results from the combined effects of the downward gas pressure gradient force, particle transport, and local formation of the high
void region. The increase in gas inflow velocity enhances the upward pressure gradient force, resulting in forward segregation.

Physics of Fluids

35

3

033313