(707f) Segregation and Mixing of Granular Mixtures in Heap Formation

Segregation and mixing of granular mixtures during heap formation have important consequences in industrial and agricultural engineering. In this study, binary mixtures of large and small spheres are poured into quasi-two-dimensional silos; the latter allow straightforward visualization of the segregation dynamics.  This work investigates a larger number and wider range of control parameters than previous studies, including particle size ratio, flow rate, flowing layer length, silo thickness, absolute particle size, and heap rise velocity.  Depending on these parameters, three different final configurations are observed: stratification, segregation and mixing.  The boundary between stratified and non-stratified states is primarily controlled by the two-dimensional flow rate, and the critical flow rate for this transition depends weakly on particle size ratio and flowing layer length.  In contrast, the transition from segregation to mixing is controlled by the rise velocity of the heap, and this critical rise velocity depends strongly on the particle size ratio.