Basic Research of a New Classification System using an Almost Rigidly Rotating Flow

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We have studied a new wet-type centrifugal classification using an almost rigidly rotating through-flow within a rotating doubled-walled container consisting of a housing and a core. Consequently, we have obtained the following main results.1.Theoretical consideration on the classification performance in an Ekman layr(1) We obtained an approximate soluiton of particle trajectories in the Ekman layr.(2) When the feed particles of all sizes are unifomly fed near the core wall, the cut size depends on the Ekman and Rossby numbers of flow (rotation and through-flow rates), the wall gradients and curvatures, and the true relative density and shape of particles, but the sharpness index is independent of these parameters.2.Experimental consideration of sub-micron classification using silica particles(1) When the Rossby number epsilon_E is 8.1*10^<-3>, the sharpness index depends on the Ekman number E,and a high sharpness index value of 1.47 is obtained for E=6.7*10^<-5>.(2) The cut size is propotional to E^<1.70>, and the sub-micron classification is realized for E*6.0*10^<-6>.3.Theoretical and experimental considerations on the withdrawal of coarse particles for application to a continuous classification(1) When the withdrawal rate is below a threshold value K_<CE> obtained by the theoretical analysis of an Ekman transport, the sharpness index is almost as good as in a no-withdrawal case.(2) On the otherhand, when the withdrawal rate is above K_<CE>, the sharpness index is also good below a critical withdrawal rate K_<CS> depending on Ekman and Rossby numbers, but it becomes extremely bad above K_<CS>.