Velocimetry in fluidized beds by ultrafast X-ray CT

Ultrafast X-ray electron beam computed tomography (CT) is an imaging technique, which has been developed for measuring phase distributions in multiphase flows. For example, two- and multiphase flow experiments in vertical pipes, conventional and slurry bubble columns, fluidized beds, monolithic structures and bundle geometries could be evaluated by this technique. With extending the measurement system towards dual-plane imaging, the option of velocity measurement has been created and applied for instance in two-phase vertical pipe flow.
In this study, we focus on measuring velocities in particulate systems. Some methods for velocity evaluation can be adapted from gas-liquid flows, such as the cross-correlation technique for determining the velocity of gas bubbles. Now, we present a technique, which allows velocity evaluation of the solid particles. This is achieved by adding marker particles with higher X-ray absorption to the particle phase and determining their velocities representatively.
In this paper, two different velocity evaluation techniques are described and selected results achieved by conducting experiments on a spout fluidized bed are presented. This combination of spouting and fluidized bed is a rather new type of particulate system, which combines the advantages of both, but whose dynamics is yet not fully understood. The capability of ultrafast X-ray CT to recover phase distributions as well as velocity information from particulate systems in order to better understand the dynamics of particulate systems is demonstrated with this exemplary experiment.