In the first part of this thesis the means are described by which an
industrial disc stack centrifuge may be scaled-down to process in a
meaningful fashion small volumes of particle suspensions. The centrifuge
separation characteristics so measured were suitable for direct scale-up
predictions of centrifuge performance. Experiments with a dye tracer and a
reduced number of discs indicated that the flow through the disc
centrifuge is influenced by the position of the separating discs within the
disc stack.
This influence was also reflected in the separation performance of a
particulate suspension. The results were shown to be in the range obtained
using a full-scale industrial disc centrifuge. Experiments also showed a
distinct trend that the flow rate and in particular the single passage
throughput influenced the separation performance. Using a non-linear
curve-fitting algorithm it was shown that the grade efficiency curve of a
disc centrifuge may be approximated by a two-parameter model equation.
In the second part of this thesis the means are described by which various
feed zones designs may be examined in respect to particle breakup using
small volumes of a diluted protein precipitate suspension. It has been
shown that in the high shear fields which are present in the feed zones to
centrifuges the precipitate particles are readily disrupted into smaller
fragments, the fragment size depending on the strength of the shear field.
Examination of three different feed zone types revealed that particle
breakup increased in the following order:
full-hermetic < hydro-hermetic < semi-hermetic
It has also been demonstrated that the bowl speed and in particular the
rotational velocity of the distributor ribs has a significant influence on
the level of particle breakup in the hydro-hermetic feed zone, while the
effects were less pronounced in the full-hermetic feed zone.
Based on the results obtained during the above studies the major mechanism
of particle breakup is thought to be due to a combination of turbulence
and collision of the particle suspension with the rotating distributor ribs.
It has been shown that the level of particle breakup is directly related to
the circumferential velocity of the distributor ribs