(408g) Powder Flow Characterization at Low Consolidation: 1. Modeling and Experimental Values of Torque Estimation

The flow properties of fine powders at very low consolidation levels are relevant to small scale industrial application of powder flow, such as in small process hoppers and mixers of pharmaceutical powders. In addition, many process applications of powder technology involve gas-solids systems. The knowledge of flow properties of aerated powders is necessary for proper handling.

Characterization of powders and granular materials can be made with a variety of commercially available shear testing devices. However, in fact, sensitivity of these shear testers has been decreased greatly at low levels stress. Furthermore, materials which these testers find to be cohesion-less may have practical differences in flow behavior, especially in regions of low consolidation stress.

New testing devices, which use non-traditional methods (such as centrifugal force) to estimate cohesive forces at low levels of consolidation stress, are not well-established and their correlation to either traditional shear testers or practical problems is incomplete. The equipment used in this research project was the state of the art powder cell purposely developed by Anton Paar to fit on an Anton Paar rheometer and carry out torque measurements on both aerated and fluidized powders. In this instrument, the state of consolidation of the powder can be adjusted by changing the impeller depth and the aeration rate. Four free flowing powders, according to the Geldart classification, Sand, Glass beads, Alumina, and Calcium lactate powders were used in this research project. The theory developed by Bruni et al. 2007 and applied by Tomasetta et al. 2011 is used to evaluate powder flow properties of the powders. Two different models considering the state of stress, active and passive state of stress, during torque measurement were considered. The results indicated that the instrument allows to successfully exploring low consolidation ranges and well correlates with the expected powder flow properties.

REFERENCES

[1] Bruni, G., Barletta, D., Poletto, M., & Lettieri, P. 2007. A rheological model for the flowability of aerated fine powders. Chemical engineering science, 62(1), 397-407.

[2] Tomasetta, I., Barletta, D., Lettieri, P., & Poletto, M. 2012. The measurement of powder flow properties with a mechanically stirred aerated bed. Chemical Engineering Science, 69 (1), 373-381.