Blade-Granule Bed Stress in a Cylindrical High-Shear Granulator: Variability Studies

The behavior of dry, steady‐state granule beds in each identified flow regime, i.e., frictional, toroidal, and fluidized, in a vertical‐axis cylindrical high‐shear granulator is studied. The granule bed behavior is discussed in terms of the blade‐granule bed interactions and bed surface behavior. The blade‐granule bed stress was measured with a custom‐built telemetric impeller pressure sensor system and simulated with the discrete element method, while the bed surface velocity and height were studied by high‐speed imaging and particle imaging velocimetry. The simulations reasonably predicted the average blade‐granule bed stresses. The variability, i.e., fluctuation amplitude and periodicity, and trends of the average values differed in each flow regime. Frequencies of the periodic bed surface velocity and height fluctuations changed from single blade pass frequency to two blade passes frequency and finally a loss in periodicity across the flow regimes. Periodic fluctuations of the blade‐bed stress were only observed in the fluidized regime until a certain impeller speed or Froude number was reached. These frequencies were slightly higher than one impeller rotation (three blade passes). The variability of the impeller blade‐granule bed stress, granule bed surface velocity, and bed height in a high‐shear granulator under frictional, toroidal, and fluidized flow regimes was studied and proved to be related to the flow regimes of the dry granule beds at different impeller speeds, granule sieve sizes, and granule bed loads. The blade‐bed stress was evaluated by discrete element method simulations.