9 Impact Comminution in Jet Mills
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Fig. 19 a–c Three consecutive images extracted from high-speed videos [time difference of 3 ms
from (a–c)]. Movement of a particle cluster away from the outer edge of a classifier blade (100 g
initial holdup, 12,000 rpm classifier speed). d Cluster formation frequency as a function of the
classifier speed (400 g initial holdup). Adapted from Köninger et al. [31], with kind permission of
Elsevier
its accumulated particles—rotates in a certain distance to the classifier wheel for
some time. Figure 20b–c show three consecutive images of this cluster type. The
formed clusters will thus interfere with the solid transport towards the classifier and
the following classification process, i.e. they can be seen as scavengers for the fine
particles.
Besides the detained fine particles, the clusters mostly consist of intermediate
particles, which are too big to pass the classifier, yet are too small to settle and reenter the grinding zone. The overall amount of clusters increases with increasing
holdups [32].