Surface morphology and shear effect on lubricated granular system

Abstract

Improving the particle surface frictional behavior is of considerable importance in several industries so as to manipulate the powder flowability and handling. In this work, we have studied the lubrication phenomena in an assembly of flowing bulk powder particles in presence of a fine powder lubricant. Experiments were conducted in two different shear environments, for two different levels of confinement and using three different bulk powder particles having distinct surface morphology. The added lubricant particles tend to adhere to the surface of bulk particles thereby altering their surface morphology. This results in altered inter-particle friction, which typically reduces for small addition of lubricant, but increases on its excess addition, thereby altering the particle flowability. While this behavior is generally understood through previous studies, the current work explores how the effect of confinement, shear environment and particle surface characteristics combine in a unique manner to provide modified flow behavior for different lubricant concentrations. Extended shear duration seems to extend the range of lubricant concentrations for improved flowability. On the other hand flow confinement seems to limit the extent of lubrication for these range of concentrations. Both these opposing effects also exhibit a unique dependence on the particle surface morphology and its seeming affinity with the lubricant particle. The parameter types and ranges explored comprise most conditions encountered in industrial systems, the outcome thereby providing a basis for designing of applications handling lubricant-particle mixtures.