Local Rheology Relation with Variable Yield Stress Ratio across Dry, Wet, Dense, and Dilute Granular Flows.

Dry, wet, dense, and dilute granular flows have been previously considered fundamentally different and thus described by distinct, and in many cases incompatible, rheologies. We carry out extensive simulations of granular flows, including wet and dry conditions, various geometries and driving mechanisms (boundary driven, fluid driven, and gravity driven), many of which are not captured by standard rheology models. For all simulated conditions, except for fluid-driven and gravity-driven flows close to the flow threshold, we find that the Mohr-Coulomb friction coefficient µ scales with the square root of the local Péclet number Pe provided that the particle diameter exceeds the particle mean free path. With decreasing Pe and granular temperature gradient M, this general scaling breaks down, leading to a yield condition with a variable yield stress ratio characterized by M.

A PEPT algorithm for predefined positions of radioisotopes relative to the tracer particle.

PEPT has been used to study the flow of material in a wide range of industrial systems. Usually, by invoking the ergodic assumption for the behaviour of the flow field, a single tracer, tracked over a sufficiently long period, can be used to characterize the velocity field of a steady state system. Starting with a known distribution of positron-emitting-radioisotope within the tracer particle, an optimised Positron Emission Particle Tracking (PEPT) algorithm for determining the centroid of the tracer is presented. A simple geometric constraint is iteratively employed to isolate only those lines of response passing through the tracer. The algorithmic approach for isolating the valid lines of response is presented within the context of PEPT experiments using stationary and moving tracers.