Effects of Air on the Segregation of Particles in a Shaken Granular Bed

摘要

Effects of interstitial air on the motions of a large intruder in a shaken granular bed are studied experimentally as a function of ambient air pressure, particle size of the bed and the density of the intruder. It is found that the intruder always rises from the granular bed in the absent of air. However the intruder can acquire both positive and negative buoyancy in the presence of air. Negative buoyancy can only be observed when both the density of the intruder and the particle size of the bed are small enough. This negative buoyancy can be explained by the unusual air pressure distribution found in the bed.