Electrical capacitance tomography measurements of gravity-driven granular flows

An electrical capacitance tomography (ECT) system is used in this study to investigate the density waves generated in the gravity-driven granular flow through a vertical pipe. The experiments are conducted in two stages. First, the time-averaged quantities of particle concentration and velocity are measured and correlated with the mass flow rate of particles. Second, the power spectra of particle concentration fluctuations are examined to determine the condition for the formation of density waves. The present work finds that the time-averaged particle concentration is higher toward the centerline of the pipe and the particle velocity is relatively uniform over the cross section of the pipe. The conducted load cell and fiber optic probe measurements are in reasonable agreement with the ECT measurements. The density wave formation has a close correlation with the local particle concentration. The experimental results also indicate that the dominant frequency might vary while the particles pass through the vertical pipe.