Size segregation entrainment

Nienow and Chiba (1981), and finally well summarized by the latter authors (1985). Misek (1971) described the hydrodynamics, entrainment, and partial flooding of fluidized systems consisting of nonuniform particles. Kennedy and Bretton (1966) studied the axial dispersion of nonuniform spheres fluidized with liquids, followed by investigations on size segregation carried out by Al-Dibouni and Garside (1979). 

In direct-compression formulation, there is a wide particle size distribution. Usually, the active drug is at the fine end of the range. Such a wide particle size range can easily result in significant segregation. Five primary mechanisms are responsible for most particle segregation problems [13]. Of these, only three typically occur with pharmaceutical powders sifting, entrainment of air, and entrainment of particles in an air stream. 

This approach is usually not practical for drops less than 100 pm, since for most situations large cross-sectional areas are needed to reduce the bulk velocity below the terminal settling velocities of such drops. An air stream with a 10 ft/s vertical velocity will entrain water drops less than about 700 pm, while a bulk velocity of 1.0 ft/s will entrain drops of about 100 pm or less. Gravity techniques can be used to remove large quantities of die latger-size dispersed-phase materia prior to some other segregation technique. 

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