Intruder trajectory tracking in a three-dimensional vibration-driven granular system:Unveiling the mechanism of the Brazil nut effect

We employ a Hall-effect magnetic sensor array to accurately track the trajectory of a single magnetic sphere,referred to as the“intruder,”within a three-dimensional vibro-fluidized granular bed to unravel the underlying physical mechanism governing the motion of the intruder.Within the acceleration range of 3.5 g≥Γ≥1.5 g,we find that,regardless of the intruder's initial position,it consistently reaches the same equilibrium depth when the vibration acceleration(Γ)and frequency(ω)are fixed.ForΓ≤2.5 g,the equilibrium position lies on the surface of the granular bed,while forΓ>2.5 g,it shifts below the surface.Additionally,intruders with different densities exhibit varying equilibrium depths,with higher density resulting in a deeper equilibrium position.To understand the mechanism behind the intruder's upward or downward motion,we measure its rising or sinking velocities under different vibration parameters.Our findings demonstrate that the rising velocity of the intruder,under varying vibration accelerations(Γ)and frequencies(ω),can be collapsed using the ratioΓ/ω,while the sinking velocity remains unaffected by the vibration strength.This confirms that the upward motion of the larger sphere,associated with the Brazil nut effect,primarily arises from the void-filling mechanism of the bed particles.Furthermore,our experiments reveal that the presence of convection within the bed particles has minimal impact on the motion of the intruder.

BUBBLE CHARACTERISTICS IN A TWO-DIMENSIONAL VERTICALLY VIBRO-FLUIDIZED BED

Measurement of bubble size and local average bubble rise velocity was carried out in a vertically sinusoidal vibre-fluidized bed. Glass beads of Geldart group B particles were fluidized at different gas velocities, while the bed was vibrated at different frequencies and amplitudes to study their effects on the bubble behavior. This is compared with the case of no vibration in a two-dimensional bed and it is concluded that with vibration the local average bubble size dbav, decreases significantly, especially at minimum bubbling velocity. The average bubble size increases slightly with increasing vibration frequency and amplitude. The local average bubble rise velocity is higher than that with no vibration, though with increasing vibration frequency and amplitude, it does not change significantly.

Fluidization of nano and sub-micron powders using mechanical vibration

The fluidization behavior of nano and sub-micron powders belonging to group C of Geldart＇s classification was studied in a mechanically vibrated fluidized bed （vibro-fluidized bed） at room temperature. Pretreated air was used as the fluidizing gas whereas SiO2. Al2O3, TiO2, ZrSi, BaSO4 were solid particles. Mechanical vibration amplitudes were 0.1, 0.25, 0.35, 0.45mm, while the frequencies were 5, 20, 30, 40 Hz to investigate the effects of frequency and amplitude of mechanical vibration on minimum fluidization velocity, bed pressure drop, bed expansion, and the agglomerate size and size distribution, A novel technique was employed to determine the apparent minimum fluidization velocity from pressure drop signals. Richardson-Zaki equation was employed as nano-particles showed fluid like behavior when fluidized. The average size of agglomerates formed on top of the bed was smaller than those at the bottom, Size distribution of agglomerates on top was also more uniform compared to those near the distributor. Larger agglomerates at the bottom of the bed formed a small fraction of the bed particles. Average size of submicron agglomerates decreased with increasing the frequency of vibration, however nano particles were less sensitive to change in vibration frequency. Mechanical vibration enhanced the quality of fluidization by reducing channeling and rat-holing phenomena caused by interparticle cohesive forces.