Toward general regime maps for cohesive-particle flows: Force versus energy-based descriptions and relevant dimensionless groups

Much confusion exists on whether force- or energy-based descriptions of cohesive-particle interactions are more appropriate. We hypothesize a force-based description is appropriate when enduring-contacts dominate and an energy-based description when contacts are brief in nature. Specifically, momentum is transferred through force-chains when enduring-contacts dominate and particles need to overcome a cohesive force to induce relative motion, whereas particles experiencing brief contacts transfer momentum through collisions and must overcome cohesion-enhanced energy losses to avoid agglomeration. This hypothesis is tested via an attempt to collapse the dimensionless, dependent variable characterizing a given system against two dimensionless numbers: A generalized bond number, Bo(G)-ratio of maximum cohesive force to the force driving flow, and a new Agglomerate number, Ag-ratio of critical cohesive energy to the granular energy. A gamut of experimental and simulation systems (fluidized bed, hopper, etc.), and cohesion sources (van der Waals, humidity, etc.), are considered. For enduring-contact systems, collapse occurs with Bo(G) but not Ag, and vice versa for brief-contact systems, thereby providing support for the hypothesis. An apparent discrepancy with past work is resolved, and new insight into Geldart's classification is gleaned.

Automated summary

The study suggests that a force-based description is more suitable for enduring-contact systems, while an energy-based description is more suitable for brief-contact systems in cohesive-particle interactions. By collapsing dimensionless variables against two dimensionless numbers, the hypothesis is supported by experimental and simulation systems, providing new insights into Geldart's classification.