Experimental Techniques

Designing minimally segregating granular mixtures for gravity‐driven surface flows

“…Previous studies show that the tendency of spherical particles to sink or rise in a bidisperse mixture can be characterized by the ratios of large to small particle diameter, R d = d l / d s (subscript l for large particles and s for small particles), and density, R ρ = ρ l / ρ s , along with the mixture volume concentration c l (or equivalently c s , as c l + c s = 1, assuming the solid volume fraction ϕ is constant) 40–44 . Unlike size or density segregation alone, where which species rises or sinks depends only on R d or R ρ but does not depend on mixture concentration, the segregation direction in an SD‐system can be concentration dependent, and a mixed equilibrium state can exist where the effects of particle size and density differences balance 26,45,46 …”

“…[40][41][42][43][44] Unlike size or density segregation alone, where which species rises or sinks depends only on R d or R ρ but does not depend on mixture concentration, the segregation direction in an SD-system can be concentration dependent, and a mixed equilibrium state can exist where the effects of particle size and density differences balance. 26,45,46 Although granular systems are challenging to study analytically compared with fluid flows because governing equations analogous to the Navier-Stokes equations for fluids are not yet fully established (although progress is being made in this direction [47][48][49][50][51][52] ), granular materials can offer a conceptual advantage compared with fluids. In many systems of practical interest-particularly tumbling and heap formation-the granular flow occurs only in thin regions of rapid flow, 53 even in large-scale industrial processes.…”