Conversion air velocity at which reverse density segregation converts to normal density segregation in a vibrated fluidized bed of binary particulate mixtures

It is well known, when binary mixtures of different-density particles of the same size are vertically vibrated or fluidized by airflow through the bottom, the particles segregate by density. Reverse density segregation occurs in the vibrated bed; heavier particles move upward and lighter ones move downward, and normal density segregation occurs in the fluidized bed; lighter particles move upward and the heavier ones move downward. In this study, we investigated the particles’ behavior in a vertically vibrated fluidized bed at various air velocity using two types of particulate mixtures of glass beads (GB) and stainless steel powder (SP) or iron powder (IP) of same size. We found that reverse segregation converts to normal segregation at a certain air velocity; here we call it “conversion air velocity”. Then, we investigated the likely origin of the conversion air velocity considering the minimum fluidization air velocity u_mf determined for the three monocomponent particles (GB, SP and IP) with and without vibration. We found that the conversion air velocity is close to the u_mf of the lower density particles (GB) with vibration, indicating that the conversion from reverse segregation to normal segregation occurs around u_mf of lighter particles with vibration.