9 Impact Comminution in Jet Mills
309
Fig. 1 Scheme of the lab-scale mill AFG 100. (1) Laval nozzles, (2) classifier wheel, (3) online laser
diffraction setup, (4) ring nozzle, (5) needle shaped capacitance probes inserted into the custommade adapter fitted into the original feed chute (6). Adapted from Köninger et al. [29], with kind
permission of Elsevier
the mill, the grinding process was interrupted, and the PSD was determined by
offline laser diffraction (Mastersizer 2000, Malvern Panalytical, UK). The holdup
was determined by weighing.
To measure the solid volume fraction (1 − ε) in the zone between the upper
Laval nozzles and the classifier, capacitance probes (5) were inserted into the
milling chamber through a customized measurement adapter which was fitted into
the original feed chute (6) (75 mm below the classifier). The capacitance probes
are sensitive to changes in the surrounding electromagnetic field caused by the
solids: These changes in the capacitance, which are converted to a voltage signal
and are further processed by a two-channel amplifier, can be related to the solids
concentration surrounding the probes. A calibration procedure is applied [30] to
convert the measurement signal to the corresponding solid volume fraction (1 − ε).
The local solid volume fraction (1 − ε) r was measured at six different radial positions
r, and the data was converted to an overall solid volume fraction as shown by Eq. 1.
309
Fig. 1 Scheme of the lab-scale mill AFG 100. (1) Laval nozzles, (2) classifier wheel, (3) online laser
diffraction setup, (4) ring nozzle, (5) needle shaped capacitance probes inserted into the custommade adapter fitted into the original feed chute (6). Adapted from Köninger et al. [29], with kind
permission of Elsevier
the mill, the grinding process was interrupted, and the PSD was determined by
offline laser diffraction (Mastersizer 2000, Malvern Panalytical, UK). The holdup
was determined by weighing.
To measure the solid volume fraction (1 − ε) in the zone between the upper
Laval nozzles and the classifier, capacitance probes (5) were inserted into the
milling chamber through a customized measurement adapter which was fitted into
the original feed chute (6) (75 mm below the classifier). The capacitance probes
are sensitive to changes in the surrounding electromagnetic field caused by the
solids: These changes in the capacitance, which are converted to a voltage signal
and are further processed by a two-channel amplifier, can be related to the solids
concentration surrounding the probes. A calibration procedure is applied [30] to
convert the measurement signal to the corresponding solid volume fraction (1 − ε).
The local solid volume fraction (1 − ε) r was measured at six different radial positions
r, and the data was converted to an overall solid volume fraction as shown by Eq. 1.