The measurement of powder flow properties with a mechanically stirred aerated bed

This paper re-examines a set of experimental data published by Bruni et al. (2007a, 2007b) [Bruni, G., Barletta, D., Poletto, M., Lettieri, P., 2007a. A rheological model for the flowability of aerated fine powders. Chem. Eng. Sci. 62, 397–407; Bruni, G., Lettieri, P., Newton, D., Barletta, D., 2007b. An investigation of the effect of the interparticle forces on the fluidization behaviour of fine powders linked with rheological studies. Chem. Eng. Sci. 62, 387–396] carried out on a mechanically stirred fluid-bed rheometer (msFBR), which was developed to study the rheology of aerated and fluidized powders. The use of aeration below fluidization allowed to carry out experiments with powders at very low consolidation levels. Two mathematical models, based on the Janssen approach to evaluate stresses in powder containers, were developed in order to relate the torque measurements in the Fluidized Bed Rheometer to the flow properties of the powders measured with standard powder flow testers. Results indicate that the models were able to satisfactorily predict the torque measured by the msFBR. The larger complexity of the Walker (1966) [Walker, D.M., 1966. An approximate theory for pressures and arching in hoppers, Chem. Eng. Sci. 21, 975–997] and Walters (1973) [Walters, J.K., 1973. A theoretical analysis of stresses in silos with vertical walls, Chem. Eng. Sci. 28, 13–21] stress analysis adopted in one of the two models did not introduce significant improvements in the evaluation of the stress distribution to justify its use. A procedure for the inverse application of the model was developed and applied to estimate the powder flow properties starting from msFBR data. The application of this procedure provided good results in terms of effective angle of internal friction and is promising for the ability of the system to explore powder flow at very low consolidation states.