SIZE SEGREGATION IN VIBRATED GRANULAR SYSTEMS - A REVERSIBLE PROCESS

The interior of a vibrated bed of mixed-size particles is examined exp erimentally, revealing segregation patterns that are considerably diff erent than the ''layered cake'' structures published in previous liter ature. The frequency of vibration has a strong effect on such patterns , which are destroyed when the vibration frequency is increased past a pproximate to 20 Hz. The segregation process is reversible; the granul ar system can be driven back and forth between segregated and homogene ous states by decreasing or increasing the vibration frequency.