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Particle-Laden Flows in Rotating Drums: The Silent Secrets

An overview of our experimental programme investigating particle-laden rimming flows is presented. Rimming flow is the flow established in a partially fluid-filled cylinder when it rotates about a horizontal axis. Rimming flow of homogeneous liquids has been studied since the late 1930s - originally due to its relevance to the pulp and paper industry. We started investigating how the dynamics of rimming flow are affected when the liquid becomes contaminated by successively increasing amounts of small, solid particles. In this context we discovered a new particle-segregation phenomenon that is accompanied by the formation of various spatial and spatiotemporal patterns. Long-term observations of the system, lasting up to about 5 weeks, have revealed the existence of very complex, but often highly symmetric, spatiotemporal pattern dynamics. In order to begin to understand the pattern formation processes and their associated dynamics we have very recently begun to investigate the flow by means of the Positron Emission Particle Tracking (PEPT). This technique enables probing the motion of a single radioactively tagged particle among thousands of other dynamically similar particles.