The Rotational Phase Separator (RPS) is a device to separate liquid or solid particles from a lighter or heavier fluid by centrifugation in a bundle of channels which rotate around a common axis. Originally, the RPS was designed in such a way that the flow through the channels is laminar in order to avoid eddies in which the particles become entrained and do not reach the walls. However, in some applications the required volume flow of fluid is so large, that the Reynolds number exceeds the value for which laminar Poiseuille flow is linearly stable. Depending on the Reynolds numbers the flow can then be turbulent, or a laminar time-dependent flow results. In both cases a counter-rotating vortex is present, which might deteriorate the separation efficiency of the RPS. This is studied by means of direct numerical simulation of flow in a rotating pipe and particle tracking in this flow. The results show that the collection efficiency for larger particles decreases due to the combined action of the vortex and turbulent velocity fluctuations, while it is unchanged for smaller particles.
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