Segregation patterns in gas-fluidized systems

Abstract

The formation of segregation patterns in initially homogeneous, fluidized, binary mixtures of particles has been studied. The adjustment of the bed depends on the proportions of fine and coarse particles in the mixture and the gas flow rate relative to the minimum fluidization velocities of the two components. The particles are immobile until the gas flow rate is sufficiently large to fluidize the mixture of particles. When the gas flow rate exceeds this critical value, alternating vertical bands of coarse and fine particles form. At a second critical gas velocity this pattern breaks down and the more familiar pattern of a mixed horizontal band on top of a layer of coarse particles forms. A phase diagram, constructed from experimental observations, shows the conditions for which each of these regimes exists. Its structure is explained in terms of the fluidization and consequent mobility of the mixture components. When horizontal bands are present, the thickness of the lower layer of coarse particles decreases with increasing gas flow rate depending on the proportion of fine particles in the bed. This, and its development, can be understood by analogy with the sedimentation of particles through a turbulent fluid. The experiments imply that the efficiency of mixing by the bubbles in the fluidized bed is very much less than that expected from gas bubbles in a liquid.

LiDAR derived morphology of the 1993 Lascar pyroclastic flow deposits, and implication for flow dynamics and rheology

“…Fluidisation of granular flows can also enhance segregation of large particles to flow perimeters (e.g. Gilbertson and Eames, 2001), thus increasing permeability in the flow borders and making it possible to develop similar instabilities which owe their formation to the dry frictional perimeter that surrounds a partly fluidised interior.…”

Oil Polymerisation and Fluid Expulsion From Low Temperature, Low Maturity, Overpressured Sediments

“…6. Gilbertson and Eames (2001) suggested that the particles are immobile until K h exceeds K f . At this point fluidisation occurs and alternating vertical bands of coarse and fine particles form.…”

Development of a multi-fluid model for poly-disperse dense gas–solid fluidised beds, Part II: Segregation in binary particle mixtures

“…The rate of segregation was very often measured by the bed freeze and dissection method, where the particles are taken from the fluidised bed layer by layer and sieved separately to measure the concentrations of the different species (Wu and Baeyens, 1998;Marzocchella et al, 2000;Formisani et al, 2001;Gilbertson and Eames, 2001). A disadvantage of this method is that it is very laborious and the results suffer from significant inaccuracies.…”