Experimental measurements and simulations of a granular flow system have been compared in detail. Positron emission particle tracking (PEPT) was used to study the motion of glass beads in a vertical axis mixer with slowly rotating flat blades. Unlike conventional techniques which are restricted to measuring the flow at the surface or a transparent wall, PEPT revealed the motion of material throughout the entire bed. The flow produced was three dimentional with vortices, and is more complicated than other granular flows that have been described previously. Discrete element method (DEM) was employed to simulate the same system using various sets of parameters for the bed material. As there are extensive three-dimentional flow data from both the experiment and the simulations, it has been possible to make comprehensive quantitative comparisons. This enabled the accuracy of the sets of assumptions for the DEM simulations to be examined. The simulations predicted the overall motion of the bed well. However no one set of assumptions was best, but that different sets predicted the detailed motion more accurately in different parts of the bed. None the less, it is evident that DEM models can now be used with some confidence to explore mixer design and performance.
- Granular materials