Velocity measurement for two-phase flows based on ultrafast X-ray tomography

The ultrafast electron beam X-ray tomography scanner ROFEX is used for the investigation of multiphase flows. Its functional principle allows us to obtain sequences of cross-sectional flow images, which shows local attenuation properties of the flow. Hence, the X-ray CT images mainly reveal the shape and interfaces of flow constituents, such as gas, liquid and solids via their X-ray contrast. It is, however, more difficult to obtain velocity information from multiphase flows. In this article we discuss different methods to extract information on the velocities of particles or interfaces as well as for continuous phase. For disperse phase velocity measurement, e.g. in gas-liquid or gas-solids flows, we employ cross-correlation based techniques using two imaging planes. Apart from the standard cross-correlation technique we developed a method and algorithm, which is capable to identify identical bubbles in the two planes giving us a unique Lagrangian particle-related velocity information. Eventually we give an example of velocity measurement in the continuous liquid phase using an X-ray contrast agent.