2024 AIChE Annual Meeting

(341a) Mixed Soft-Rigid Granular Flows: Role of Soft Particles in Inducing Metastable Arches

Authors

Hashmi, S. - Presenter, Northeastern University
Alborzi, S., Northeastern University
Mixing soft and rigid in the flow of granular particles in a 2D hopper reveals interesting, counter-intuitive features about the role of each particle type in flow and clogging; in stable arches that cause permanent clogs, the arch composition i.e. the probability of soft or rigid particles composing a stable arch is equal to the composition of the original mixture [1]. Also, arch shapes vary more in rigid particles than the soft, giving higher chances to the rigid to form a clog [2]. However, not all arches are stable when introducing soft particles to the ensemble. Metastable arches occur when a set of particles meet near the exit and collapse spontaneously with some delay. We characterize this phenomenon in the discharge of mixed cm-sized soft and rigid particles in a top-down symmetrical 2D hopper.

We find that perfectly rigid ensembles flow faster but clog more, while soft particles drain more slowly and intermittently with less clogging: a well-known notion in granular flows saying “Faster is slower!”. The distribution of time intervals t between the exiting particles exhibits a power-law behavior regardless of the mixture composition. Although soft particles are less stable in permanent arches, we show that they are equally stable as rigid particles in metastable arches, rather the lowest angle between the arch particles determines which particle is stable the least.

[1] Alborzi, S., Clark, B.G. and Hashmi, S.M., 2022. Soft particles facilitate flow of rigid particles in a 2D hopper. Soft Matter, 18(21), pp.4127-4135.

[2] Alborzi, S., Abrahamyan, D. and Hashmi, S.M., 2023. Mixing particle softness in a two-dimensional hopper: Particle rigidity and friction enable variable arch geometry to cause clogging. Physical Review E, 107(2), p.024901.