Separation of fine particles using rotating tube with alternate flow

Abstract

A new method for selective separation of fine particles was developed by using a rotating tube with alternate flow (RAF). The separation is performed in the condition of negligible small of the centrifugal force of a particle compared to gravity. In the horizontal tube with stable flow, each particle moves along the flow drawing a helical path. The locus of each particle depends on a parameter Aω/V0, where A is a radius of the tube, ω is its angular velocity, and V0 is the sedimentation velocity in a liquid at fixed temperature. The velocity along the flow is determined by the locus and the distribution of the flow speed in the tube. The ratio V/Umax (where V is the particle velocity and Umax is the flow speed at the tube center) was obtained theoretically and experimentally. The value took the maximum at Aω/V0≂2 and decreased near exponentially within the range of Aω/V0≳2.5 and precipitously decreased within Aω/V0≲2. By using an alternate flow method with suitable rotation for each directional flow, large particles were taken out successively in descending order of the size from one end and small ones in ascending order from the other end.