Analysis of fluidization and shear conditions in rotary-fluidized beds under dry and wet conditions

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In this project, the particle dynamics in dense sheared granular flows should be described by taking the example of a rotor granulator. For this aim the gas-particle flow will be characterized by means of the Discrete Element Method (DEM) coupled with the Computational Fluid Dynamics (CFD), whereby the Magnetic Particle Tracking (MPT) will be used for the validation of the simulations. The application of DEM based simulations will provide a detailed insight in the particle dynamics, interactions and mechanical stresses (e.g. particle rotation, collision velocities, forces and frequencies). Mathematical models describing the influence of process and material parameters on the dynamics of single particles in the granulation and coating should be developed and implemented in the DEM. The central element of this project is the characterization of the influence of the presence of a liquid on the particle dynamics by experimentally validated simulations. A liquid bridge model, which contains the capillary and viscous forces acting between wetted particles during normal and oblique impacts, should be developed and implemented. The MPT method, used for the capturing of the three-dimensional movement of the particles, is a highly innovative method for characterization and monitoring of dense granular flows (for spherical and non-spherical particles). So far, the particle movement in dense granular flows could be well characterized with very expensive experimental setups, such as Positron Emission Particle Tracking (PEPT). With the MPT method, used in this project, for the first time not only particle velocities and accelerations, but also the particle rotation can be measured, which cannot be captured or sufficiently resolved with other available methods. The measuring range of the MPT has to be extended to smaller particle sizes. This will be achieved by redesign of the measurement set-up and improved shielding against external magnetic fields, including the earth's magnetic field. Marker particles with properties tailored to physical properties of bed particles should be manufactured by means of fluidized bed coating and used in the measurements. On the basis of spray granulation and coating experiments the results from the simulations and experimental studies will be evaluated with respect to the granule growth rate and the coating quality.