Despite the industrial importance of powders and other granular materials, particulate processes remain exceedingly difficult to model, design, and control. This is due to the fact that powders often exhibit complex and diverse bulk-scale behaviors which lack fundamental understanding. While bulk-scale behavior originates from interactions among individual particles and their interaction with a medium, constitutive relationships relating particle properties, particle interactions, and bulk-scale behavior are generally unattainable.
In order to address these scientific deficiencies, powder flowability is investigated in the current study in an attempt to relate particle properties to bulk powder behavior. Powder flowability is a particularly important bulk scale property and can affect unit operations such as feeding/transfer, mixing, coating, and fluidization among others which directly influence product quality and ease of processing across a variety of industries.
This study finds that the granular Bond number, a parameter which quantifies inter-particle cohesion as the ratio of the cohesive van der Waals force to particle weight, correlates well with the flow function coefficient, a metric commonly used to assess powder flowability. As a major novelty, a granular Bond number for multi-component mixtures (i.e. powder blends) is formulated and successfully used to predict the flowability of binary and ternary powder mixtures. Since the multi-component granular Bond number takes into account particle properties and particle interactions of all components in the powder blend, this novel approach shows good predictability for the flowability of powder mixtures. This modeling effort was found to be most applicable to fine cohesive powders which are dominated by the van der Waals force. This typically includes particles with diameters ~100 μm and smaller and more generally for materials with Bond numbers greater than one.
Accordingly, the flowability model put forth in this study can be used to determine the effect of particle properties on powder flow behavior of individual materials or to predict the flow behavior of powder blends. More generally, it is anticipated that the effort to correlate particle properties, particle interactions, and bulk powder behavior as accomplished in this study will generate greater understanding of the complex behavior of powders and other granular materials.