The effects of cohesion on freely falling granular jets

Cohesive granular systems are hard to pour, which may be familiar from trouble controlling the pouring of powders such as flour while baking. Flow is often broken up into chunks ranging from the particle diameter to many times the particle size, causing both irregular flow and clogs near apertures. In this study, we describe the behavior of granular jets released from a circular aperture at the bottom of an axisymmetric silo. We perform experiments controlling the cohesive strength, the diameter of the grains, and the size of the aperture to construct a phase diagram describing the different flowing states observed. Cohesion arising from capillary bridges of water or mineral oil is compared with interparticle cohesion induced by a polymer coating. The profiles of the freely falling jets are described. The presence of interparticle cohesion causes the granular jet to break up into agglomerates. By controlling the added cohesion, the agglomeration can be controlled, evidencing a Rayleigh-Plateau like instability for a cohesive granular filament.