In this study, experimental results of an air-water trickle bed are obtained using Electrical Capacitance Volume Tomography (ECVT) system. Particularly, polished glass beads and porous clay beads are used as the solid phase respectively. The images of phase distribution in trickling and pulsating regimes are captured by ECVT. The non-uniform liquid distribution in the trickling regime is investigated.  The trickling-to-pulsating transition boundary is captured. In the pulsating regime, detailed 3-D pulse structure, pulse travelling velocity, average liquid holdup and holdup inside gas-rich and liquid-rich regions, respectively, are measured and compared. Based on a simplified mass-balance model, the linear liquid velocities inside the gas-rich and liquid-rich regions are estimated.  The physical nature of the pulsating follow is discussed.

ECVT is a novel process tomography technology recently developed based on Electrical Capacitance Tomography (ECT) which can provide direct 3-D imaging. By designing capacitance plates with inherit 3-D features, real-time inter-electrode capacitances can be directly related to the phase distribution inside the column. Its non-invasive nature makes it a suitable tool for multiphase flow research. In the present study, an air-water trickle bed packed with glass and clay beads respectively is investigated using ECVT. The non-uniform liquid distribution in the trickling regime is investigated first. Then the trickling-to-pulsating transition boundaries are obtained for both types of beads. In the pulsating regime, a 3-D body-tail pulse structure is observed, which is composed by a relatively sharp and flat leading edge, a relatively uniform body and a non-uniform tail. The quantitative results confirm that the pulse travelling velocity depends almost entirely on the gas flow rate. The average liquid holdup is influenced by both the gas and liquid flow rates, but inside a single pulse unit with one gas-rich region and one liquid-rich region, the liquid holdups in these two regions are independent of the inlet liquid flow rate when the gas flow rate is constant. This result indicates that the inlet liquid flow rate only affects the length ratio of the gas-rich and liquid-rich regions in the pulsating regime. Based on a simplified model, the linear velocities inside the gas-rich and liquid-rich regions are estimated. The physical nature of the pulsating flow is also discussed.