Break-up of granular jets due to cohesion

Cohesive granular materials are hard to pour, which may be familiar from trouble in the pouring of powders such as flour while baking. Flow is often broken up into agglomerates of a wide variety of sizes that can be much larger than the particle, also resulting in more frequent clogs near apertures. In this study, we describe the behavior of cohesive and of cohesionless granular jets released from a circular aperture at the bottom of an axisymmetric silo. We perform experiments varying the kind of cohesion, and the size of the grains and the apertures to construct a phase diagram describing the different flowing states observed. Our experiments show that the mass flux of cohesive grains is always smaller than the cohesionless case. The average volume fraction is also smaller for cohesive grains released in the jet, which further affects its geometry. The presence of interparticle cohesion causes the granular jet to break up into agglomerates. By controlling the cohesion introduced, the agglomeration can be controlled, evidencing a Rayleigh-Plateau-like instability.