Vibration-induced granular segregation in a pseudo-2D column: The (reverse) Brazil nut effect

The segregation of nine different disk-shaped intruders in a pseudo-2D granular bed consisting of 0.85 mm polystyrene beads under the influence of vertical vibrations was studied. The intruders used were all fabricated of brass and were much denser than the polystyrene particles. Depending on the vibration amplitude and frequency, intruders were able to segregate to the top or bottom of the granular bed as long as the vibration intensity Γ was greater than 1. At a fixed vibration amplitude, upward segregation, also known as the Brazil nut effect, occurred at a much higher frequency than downward segregation, which is also known as the reverse Brazil nut effect. Segregation to the top was always much quicker than segregation to the bottom irrespective of size and mass of the intruder used. By the use of high-speed video movies, it was found that the disk-shaped intruders rose along the bed height by a void filling mechanism.