Growth of a wet agglomerate rolling down an inclined granular bed

Drum granulation is a size-enlargement process in which liquid binder is sprayed on to granular material for the nucleation of wet agglomerates bound by the capillary and viscous force of the liquid. The rotation of the drum causes the relative motion of the agglomerates with respect to the surrounding granular material leading to their densification as well as their growth, and/or breakage. The granular flow in a rotating drum is characterized by a solid like bulk region which undergoes rigid body rotation and a small fluid-like flowing layer near the free surface with sufficient shear during the flow. To gain a deeper understanding of the behaviour of the wet agglomerates within the flowing free surface layer region, we investigate the growth of a single wet agglomerate placed in a granular bed in an inclined periodic chute. In order to investigate the role of the process parameters and the material properties, we study the effect of the initial granule size, liquid content, binder surface tension and binder viscosity on the granule growth. We find that the granule growth increases with the initial granule size and binder surface tension. The effect of liquid content on growth rate suggests a liquid limit beyond which increasing liquid content does not increase the growth rate. Increasing the viscosity of the liquid binder leads to a distinct granule growth behavior characterized by alternating slow and rapid growth periods.