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CFD simulations of the airfl ow in cases of different
equipment designs: (a) pre-distributor; (b) ceramic ball
packing; and (c) bottom plenum air inlet (reprinted
from Depypere et al., 2004; with permission from
Elsevier)
Figure 7.13
non-homogeneous airfl ow towards the distributor, and possible
confi guration changes that might improve airfl ow conditions were
investigated. It was found that inclusion of a pre-distributor or ceramic
ball packing layer, or the relocation of the air inlet from the side to the
bottom of the chamber, could be potential solutions for achieving
homogeneous airfl ow conditions (Figure 7.13).
The Wurster processor is a type of bottom-spray fl uid bed processor
with characteristic design, making it suitable for tablet and pellet coating,
or it can be used for production of fi ne agglomerates (Figure 7.14). It is a
kind of spouted bed system with a characteristic draft tube in a lower
central part of the processing chamber. An air distributor plate has a
larger area of the openings in the central region, below the draft tube,
leading to characteristic movement of particles within the chamber. The
particles fl uidized in the annular part, between the draft tube and the
chamber, are conveyed pneumatically in a vertical direction. The particles
are sprayed within the draft tube, and then particle velocity is reduced in
the upper expansion chamber, leading to the return of particles towards
the annular part, that is, towards the bottom of the fl uidizing chamber
(Fukumori and Ichikawa, 2006; Dixit and Puthli, 2009).
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