The drops of void fraction with increasing gas inflow velocity in reverse density segregation within a vibrated fluidized bed

Zhaohua Jiang, Keyu Yue, Hanqiao Che, Jun Oshitani, Takuya Tsuji

This study investigates the void fraction behaviors of binary particles with the same diameter but different
densities in a vibrated fluidized bed under the same vertical vibration condition with varying gas inflow velocities.
Using coarse-graining non-inertial CFD-DEM simulations, the study explores the occurrence of reverse
segregation and its effects on void fraction drops. Reverse segregation is observed when the gas inflow velocity is
below the minimum fluidization velocity (umf) of the light particles, leading to the accumulation of heavier
particles above the lighter ones. As the gas inflow velocity increases, the void fraction of the bed decreases for
both particle types, with the reduction being more pronounced for the heavier particles. The underlying
mechanism involves the interaction between the upward gas flow and the movement of the particles: for heavy
particles, the gas inflow retards their downward motion, leading to a denser bed and a significant void fraction
drop. For light particles, the gas inflow tends to fluidize them, but the presence of the heavier particles above
them prevents further dispersion, resulting in a slight void fraction decrease. These findings provide insight into
the complex dynamics of binary particle segregation in vibrated fluidized beds, highlighting the differential
effects of gas inflow velocity on void fraction behavior for particles of different densities.

Applied Thermal Engineering

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