(109a) The Vagaries of Granular and Particle Laden Flow

In the 80s, the development of the kinetic-collisional theory for granular flow (KTGF)represented a major breakthrough in the modelling of the hydrodynamics of particulate flow: based on the analogy between solid particles and gas molecules, a kinetic theory was proposed which produced constitutive equations for rapid granular flow when binary, instantaneous and inelastic particle collisions occur. In practical situations, however, the flow of particles presents complexities that escape successful description based on the KTGF alone. Many complicated phenomena happen at the meso-scale, the scale between “small” and “large”: as an example, clusters and agglomerates are formed at a length scale between particle size and equipment size. In addition, particle-particle interactions, other than inelastic and instantaneous collisions, might occur, and more complex theories are needed to capture the observed behaviour.

The talk will describe the journey from the first rigorous effort to model granular and particle laden flow to recent theories and models to explain the vagaries observed in practical situations. Open problems, in need of a solution, will be presented and the search for a “unifying” theory will be discussed.