480
R. Ahrens et al.
Fig. 1 Schematic of the
benchmark experiment in the
helically coiled flow
tube (HCT) crystallizer
the crystal projections, which were recorded at the tube outlet by the flow-through
microscope. Further, the crystal shape and a size descriptor were estimated from the
projections. Crystal velocities were calculated from the measured residence times
and known geometry of the HCT and are depicted in Fig. 2. They were measured
in an HCT crystallizer made of glass (length of 35 m, upward flow). Mean crystal
velocities were calculated for several size classes. It was observed that large crystals
of about 200 μm size are faster than smaller crystals of a size of about 100 μm. This
observation holds for crystals of a density which deviates from the fluid density at
laminar flow rates in HCTs [66, 67]. In the PBS, the residence time can be empirically described in dependence on the crystal size by a polynomial function or by
interpolation from measurements. To apply the model in a size range that exceeds
50 100 150 200 250
x in µm
0
0.2
0.4
u in m/s
u f
u p
50 100 150 200 250
x in µm
0
0.2
0.4
u in m/s
u f
u p
Fig. 2 Crystal-size dependent crystal velocities at two different laminar average fluid velocities
(blue, dashed) for the uni-variate potash alum. Measured in experiments (black, solid) and extrapolated (black, dotted)
R. Ahrens et al.
Fig. 1 Schematic of the
benchmark experiment in the
helically coiled flow
tube (HCT) crystallizer
the crystal projections, which were recorded at the tube outlet by the flow-through
microscope. Further, the crystal shape and a size descriptor were estimated from the
projections. Crystal velocities were calculated from the measured residence times
and known geometry of the HCT and are depicted in Fig. 2. They were measured
in an HCT crystallizer made of glass (length of 35 m, upward flow). Mean crystal
velocities were calculated for several size classes. It was observed that large crystals
of about 200 μm size are faster than smaller crystals of a size of about 100 μm. This
observation holds for crystals of a density which deviates from the fluid density at
laminar flow rates in HCTs [66, 67]. In the PBS, the residence time can be empirically described in dependence on the crystal size by a polynomial function or by
interpolation from measurements. To apply the model in a size range that exceeds
50 100 150 200 250
x in µm
0
0.2
0.4
u in m/s
u f
u p
50 100 150 200 250
x in µm
0
0.2
0.4
u in m/s
u f
u p
Fig. 2 Crystal-size dependent crystal velocities at two different laminar average fluid velocities
(blue, dashed) for the uni-variate potash alum. Measured in experiments (black, solid) and extrapolated (black, dotted)