Fluctuations, stratification and stability in a liquid fluidized bed at low Reynoldsnumber

Abstract

The sedimentation dynamics of extremely low polydispersity, non-colloidal, particles arestudied in a liquid fluidized bed at low Reynolds number, . When fluidized, the system reaches a steady state, defined where the local averagevolume fraction does not vary in time. In the steady state, the velocity fluctuations and theparticle concentrations are found to strongly depend on height in the particle column.Using our results, we test a recently developed stability model (Segrè 2002 Phys. Rev. Lett. 89254503) for steady state sedimentation. The model describes the data well, andshows that in the steady state there is a balancing of particle fluxes due to thefluctuations and the concentration gradient. Some results are also presented for thedependence of the concentration gradient in fluidized beds on particle size; thegradients become smaller as the particles become larger and fewer in number.