Torque Measurements in Aerated Powders Using a Mechanically Stirred Fluidized Bed Rheometer (msFBR)

This paper reports on a study of the flow properties of two aerated/fluidized granular materials by means of torque measurements using a mechanically stirred fluidized bed rheometer (msFBR). The paper presents the experimental procedures developed to test two different materials below the minimum fluidization condition and when the powders are just fluidized. The dependency of the torque measurements upon impeller speed and stirring time was analysed. The effect of changing rate of aeration and impeller depth in the bed was also systematically investigated. Results reported here were obtained on an alumina powder and on ballotini belonging to Geldart group A and B respectively. Below minimum fluidization, the torque profiles obtained for both powders were independent of impeller speed. With increasing impeller depth the torque profiles resembled the normal stress profiles in silos. At minimum fluidization condition, the torque was found to be dependent on the impeller speed and found to increase linearly with increasing impeller depth.