Qualitative Observations of Dense Particle Motion in a Vibration-Excited Granular Bed

The Brazil nut effect is a classic phenomenon in which larger objects typically migrate to the top of a bed of smaller granular media when exposed to vibration. An example of this phenomenon is finding Brazil nuts on the top of a can of mixed nuts. In this study, the Brazil nut problem is simulated by submerging a large particle in a bed of granular media and then subjecting the system to vibration. Stereoscopic X-ray imaging is used to visualize the large particle motion. These images are then compiled into movies where the particle motion may be tracked. Observations of the large particle motion are made under varying conditions of large particle material, vibration frequency, and bed height. Particle percolation, where smaller particles fill small voids beneath the large particles, is the dominate mechanism at higher vibration frequencies. However, as the frequency decreases, or as the disparity between the densities of the large and small particles decrease, the effects of convection become more pronounced.Copyright © 2007 by ASME