Patterns of particle segregation

Perfect mixing therefore is represented by M = 1. Incidentally this definition of mixing index should not be confused with those mixing 

Nienow et al. (1978) showed fhaf the relationship between mixing index and gas velocity could be written as 

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). 

The quantity Ujo has been correlated with the minimum fluidizing velocity, particle size, sphericity and density of the two kinds of 

For the case of equal density but differently sized particles fluidized in a bed with a nozzle-type distributor, Geldart (1992) recommends operating the bed at a gas velocity of 1.5 Ucf, where m / is the minimum velocity for complete fluidization, which may be well above the minimum fluidizing velocity found by the usual experimental method. 

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