9 Impact Comminution in Jet Mills
327
Fig. 10 Number-weighted contact number (a) and relative impact velocity distributions (b) for
different process times in a fluidized bed jet mill (one nozzle). c Stress numbers SN % and SN stress
for the respective distributions. d SEM image of one probe particle after 40 min. 200 m s −1 gas
velocity at the nozzle threat. Adapted from Strobel et al. [33], with kind permission of Elsevier
Nozzle Arrangement
The next set of experiments targeted the change in the stressing behavior for two
opposing nozzles. Additionally to the increase in number, the distance of the nozzle
was systematically varied. Figure 11 again shows the cumulative number-weighted
sum distributions for the contacts (a) and the relative velocity (b) for normalized
nozzle distances (z · d
−1
0 ) of 10 and 21, respectively. As a reference, the corresponding
distributions for the single nozzle setup from the previous section are given.
The opposing jet setup shows higher contact numbers (a) and higher relative
impact velocities (b) after a processing time of 10 min. The configuration with the