Helical inner-wall texture prevents jamming in granular pipe flows.

Granular pipe flows are characterized by intermittent behavior and large, potentially destructive solid fraction variations in the transport direction. By means of particle-based numerical simulations of gravity-driven flows in vertical pipes, we show that it is possible to obtain steady material transport by adding a helical texture to the inner-wall of the pipe. The helical texture leads to a more homogeneous mass flux along the pipe, prevents the emergence of large density waves and substantially reduces the probability of plug formation thus avoiding jamming of the particulate flow. We show that the granular mass flux Q through a pipe of diameter D with a helical texture of wavelength λ follows the equation Q = Q0·{1 - B sin[arctan(2πD/λ)]}, where Q0 is the flow without helix, predicted from the well-known Beverloo equation. Our new expression yields, thus, a modification of the Beverloo equation with only one additional fit parameter, B, and describes the particle mass flux with the helical texture with excellent quantitative agreement with simulation results. Future application of the method proposed here has the potential to improve granular pipe flows in a broad range of processes without the need for energy input from any external source.