Experimental study of a granular flow in a vertical pipe: A spatiotemporal analysis

The spatiotemporal characteristics of the flow of 125 μm glass beads have been studied experimentally in a 2.9 mm diameter vertical glass pipe by means of a digital linear charge coupled device camera. The dynamics and propagation of granular density fluctuations have been analyzed in various flow regimes for different values of the granular mass-flow rate and of the degree of humidity H. At low flow rates, the granular flow has a high compactness and periodic intermittency effects occur at high H values: a pulsating bubble appears at the top of the flow channel and its time dependence is studied. At higher granular flow rates, a wave regime is observed with alternate low and high compactness regions: at low H values, the wave velocity is constant with time and can be measured precisely from the spatiotemporal diagrams. At higher humidity contents, periodic oscillations of the wave system are observed: at high amplitudes, transient blockages of the flow and a stick-slip displacement mode have been identified.