The Global Property of the Dilute-to-Dense Transition of Granular Flows in a 2D Channel

Summary The dilute-to-dense transition of granular flow of particle size d 0 is studied experimentally in a two dimensional channel (width D) with confined exit (width d). It is found that there exists a maximum inflow rate Q c, above which the outflow changes from dilute to dense and the outflow rate Q(t) drops abruptly from Q c to a dense flow rate Q d. The re-scaled critical rate $$ D/d_0 $$ is found to be a function of a scaling variable λ only, i.e. q c ∼ F(λ), and $$ \lambda \equiv \frac{d} {{d_0 }}\frac{d} {{D - d}} $$ . This form of λ suggests that the dilute-to-dense transition is a global property of the flow; unlike the jamming transition, which depends only on $$ \frac{d} {{d_0 }} $$ . The transition is found to occur when the area fraction of particles near the exit reaches a critical value 0.65±0.03.