(22a) Analysis of Dynamic Flow of Cohesive Particles

Particulate flow of granular materials is usually such that cohesion is not negligible. Inter-particle forces, including van der Waals forces, capillary (liquid bridge) forces, sintering, electrostatic forces, and frictional forces contribute towards the properties of particles and aggregates in hoppers, risers, packed and fluidized beds and in pneumatic conveying.

In shear flow of uniformly sized particles, inter-particle forces and hydrodynamic forces dominate. The properties of the system depend on two dimensionless numbers. The first one is related to the shear state imposed to the material. The second one characterizes the intensity of the cohesion. the macroscopic angle of friction at the peak state can be split into three distinct terms of collisional, frictional and dilational origins.

In a square well cohesive model, different regimes are present depending on the magnitude of cohesive forces and solid fraction. Agglomeration from inelastic collisions (elastic-plastic) is simulated by decrease in number of particles but increase in size of the particles affecting frequency of inter-particle collisions.

Shear stresses and normal stresses are compared against experiments in a shear cell (Freeman tester) using particles of different diameters, cohesive strength and dynamic friction.