Centrifugal classification of ultrafine particles: Influence of suspension properties and operating parameters on classification sharpness

• Intense circulations close to the inlet turn into a developed flow profile downstream.
• Distribution of an injected tracer was visualized using CFD simulations.
• Sharpness of classification strongly depends on the chosen operating parameters.
• Constant sharpness is obtained by adequate pretreatment at higher concentrations.

The key principle underlying classification in centrifuges is the superposition of an axial-flow velocity and a radial, particle size-dependent settling velocity. These velocities are influenced by adjustable parameters, whereby a certain particle size is defined as cut size. Therefore, this separation process is determined by residence time. Our study addresses the question as to how the classification quality depends on the various setting options of the process. Experimental measurements of the residence time distribution and CFD simulations provide a comprehensive picture of the flow conditions. Besides the velocity profile determination, the latter method is used to visualize the distribution of the product fed in the rotor.Additionally, a characterization of the sedimentation behavior of a selected product is made based on a one-dimensional convective particle-transport equation. Solids concentration and state of stabilization are taken into account. The findings of both flow field and sedimentation analysis are compared with the corresponding results from classification experiments.