Segregation Fluidization

Eq. (15) and 1.1 10- 7 m2/s according to Eq. (14). This significant difference may be explained by the fact, the Kang et al. used particles of uniform size whereas van der Meer et al. measured dispersion between two fractions of different particle size in a segregated fluidized bed. As adsorption in a frontal mode is performed using classified or otherwise stabilized fluidized beds, the lower Daxp resulting from van der Meer s correlation may be a better description of the solid phase dispersion in a fluidized bed for protein adsorption. 

The flow required to maintain a complete homogeneous bed of sohds in which coarse or heavy particles will not segregate from the fluidized... 

Nienow and Chiba, Fluidization, 2d ed., Wiley, 1985, pp. 357-382, for a discussion of segregation or mixing mechanism as well as the means of predicting this flow also see Baeyens and Geldart, Gas Fluidization... 

Figure 2.3 Segregation pattern in a flotsam-rich system. Reprinted from Davidson, J.F., Clift, R. and Harrison, D., Fluidization, ed.. Academic Press, 1985, with permission from Elsevier.

In equation 2.28 Up is the lower of the two minimum fluidizing velocities of the two types of particle in the mixture and Ufo is the velocity at which mixing takes over or begins to dominate segregation. Thus, as the superficial gas velocity in the bed is increased, the mixing index increases from M = 0 at the lower minimum fluidizing velocity (m = Mp), where the bed is quiescent with no particle movement because of the absence of bubbles, to M = 0.5 when, by definition, the velocity is equal to Uto- The mixing index approaches a value of unity as the velocity increases still further (Nienow and Chiba, 1985). 

Segregation of the mix This mix can occur when larger doses of the admixture are added to offset the lack of initial fluidizing of the concrete or to reinstate workability. The segregation phenomenon is always related to a superplasticizer overdose, beyond the saturation point. In some instances the surface of the hardened concrete is covered with a white layer composed... 

Three-phase (solid/liquid/gas) fluidized systems are also of some practical importance. There is again a strong analogy between the rise of gas bubbles in normal liquids and in liquid fluidized beds (Dl, R3), although there is evidence of solid/liquid segregation in wakes (R3, S6) which has no parallel for two-phase systems. 

Figure 5 Fluidization segregation can take place when a bed of aerated material settles, driving fines to the top of the bin.

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