Effect of Microscopic Properties on Flow Behavior of Industrial Cohesive Powder

Abstract

The characteristics of powders on a bulk scale are heavily influenced by both the material properties and the size of their primary particles. Throughout the stages of storage and transportation in the powder processing industry, various forms of deformation and stress, such as pressure and shear, impact these materials. Recognizing the point at which a powder undergoes yielding becomes particularly significant in numerous applications. There are also times when the level of stress needed to maintain it must be understood. The measurement of powder yield and flow properties remains a challenge and is addressed in this study. As part of the European collaborative project, a number of shear experiments were performed using two shearing devices: the Schulze ring shearing device and the Anton Paar Powder Cell (APCC). These experiments have three purposes: (i) test reproducibility/consistency between two shear devices and test protocols; (ii) relate bulk behavior to microscopic particle properties, focusing on bulk density and thus the effect of cohesion between particles; and (iii) investigate the influence of the temperature of heated powders on the powder’s flow properties, which is important for industrial reactors. Interestingly, for samples with small particle sizes, bulk cohesion increases slightly, but bulk friction increases significantly because of particle interaction effects. The experimental data not only provide useful insight into the role of microscopically attractive van der Waals gravitational and/or compressive forces on the macroscopic flow behavior of bulk powders but also have industrial relevance. We also provide robust data of cohesive and attritional fine powder for silo design used for calibration and validation of silos, models, and computer simulations.