In the last decade a major progress has been achieved in the synthesis and functionalization of nanoscale particles, but the handling of such material systems like separation or classification has ...been neglected. With tubular centrifuges, even nanoscale particles can be separated from a suspension at reasonable throughputs due to very high g values. This is a great advantage compared to membrane techniques (low throughput) and filtering, disc stack and decanter centrifuges (lower g values). An analysis of the discharged solids in dependence on time and verification of sediment build‐up with a magnetic resonance spectrometer (MRI) provide a comprehensive understanding of the sedimentation process in a tubular bowl centrifuge. MRI allows a noninvasive, direct view into the filled centrifuge rotor; this data is compared with theoretical results.
The separation of colloidal particles from dilute suspensions is a difficult but crucial task. Since the application of nanoscale particles becomes significantly more important. The focus of this work is to link the mechanisms of sediment build‐up with the sedimentation performance of tubular bowl centrifuges.
This work contributes to the field of solid‐liquid separation in focusing on the screening of colloidal particles in a semicontinuous process. The aim of the study is to provide the basics for a ...continuous classification process in industry. After a short introduction to the field of particle screening, a review of the possibilities of classification in the gas or liquid phase is presented, including analytical methods, devices for the fractionation on the laboratory scale as well as apparatus for screening on the pilot and industrial scale. The results show the dispersion, stabilization and classification of fine kaolin and polystyrene particles. Kaolin was used to demonstrate the possibility of removing the fraction of fine particles, polystyrene particles were used to investigate the removal of the coarse fraction. The diameter of the particles used in this study ranges from 250 nm to 3 μm.
The introductory part of the paper reviews the techniques available for the classification of particles in the gas and liquid phase. Furthermore, the limitation of screening by sedimentation due to diffusion is exemplified. The main part deals with the screening of colloidal polystyrene and fine kaolin with a semicontinuous centrifuge.
The classification of dispersed particles below 1 μm is a difficult task due to the high surface area‐to‐volume ratio. Tubular‐bowl centrifuges offer high centrifugal numbers, which enable the ...separation and classification of fine particles, biological cells and cell debris. This work presents the classification of two fine products with a mean particle size below 1 μm. Polydisperse silica and polystyrene were split successfully into a fine and a coarse fraction by a semi‐continuous tubular‐bowl centrifuge. The fine fractions exhibited narrow particle size distributions. An optimization of the process could be achieved by a comprehensive understanding of the flow patterns, which are accessible with computational fluid dynamics. The axial and tangential velocity profiles were calculated for rotational speeds up to 40,000 rpm and throughputs ranging from 0.1 to 2 L/min.
This work demonstrates the classification of fine particles in suspension with a semi‐continuous tubular‐bowl centrifuge. Furthermore, the flow patterns in the rotor of the centrifuge are calculated by computational fluid dynamics for rotational speeds up to 40,000 rpm and throughputs ranging from 0.1 to 2 L/min.
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