This paper presents a new model of the separation of fine particles in the cylindical part of decanter centrifuges. It assumes, that particle sedimentation in this continuously operating centrifuge does not reach the equilibrium with particle-particle contact, but that a layer of still settling particles exists. This layer is located between the clear suspension fluid and the settled solids near the bottom of the bowl, which are able to be convered by the screw due to sufficient sludge consistency. Compared with the suspension fluid, this layer is of higher density and viscosity. Simultaneously it is not very stable against shear stress of the fast flowing clear suspension flued, Therefore this layer is responsible for the sudden worsened separation if one increases the troughput over a certain critical value.
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