In the production and processing of granular matter, mixing of solids plays an important role. Granular materials such as sand, polymeric particles and fertilizers are processed in different apparatus such as fluidized beds, rotary kilns and spouted beds. In the operation of these apparatus proper mixing is essential, as it helps to prevent formation of hot-spots, off-spec products and undesired agglomerates. DEM can be used to simulate these granular systems in detail and provide insight in mixing phenomena. Several methods to analyse and characterize mixing on basis of DEM data have been proposed in the past, but there is no general consensus on what method to use. In this paper we discuss various methods that are available to give quantitative information on the solids mixing state in granular systems based on DEM and TFM simulations. We apply the different methods to full 3D DEM simulations of a fluidized bed and to tracer particles in full 2D TFM simulations. It is found that some of these methods are grid dependent, are not reproducible, are sensitive to macroscopic flow patters and/or are only able to calculate overall mixing indices, rather than indices for each direction. We compare some methods described in literature and in addition propose two new methods, which do not suffer from the disadvantages mentioned above. Simulations are performed for seven different operating pressures. It is found that mixing improves with operating pressure caused by increased porosity and increased granular temperature of the particulate phase.
|Title of host publication||Proceedings of the 7th International Conference on Computational Fluid Dynamics in the Minerals and Process Industries (CFD 2009), 9-11 December 2009, Melbourne, Australia|
|Place of Publication||Melbourne|
|Publication status||Published - 2010|