Methods for extraction of velocity information from ultrafast X-ray tomography

The ultrafast electron beam X-ray tomography scanner “ROFEX” is widely used for investigations on multiphase flows, such as two-phase pipe flow, bubble columns, flows in structured packings, in monolith ceramics, in foams, in rod bundle geometries and others. The use of X-rays allows to discriminate phases, i.e. to distinguish between gas and liquid, gas and solid, liquid and solid and so on. It is, however, more difficult, to obtain velocity information from two-phase flows. Measuring velocities in the continuouse phase is only possible, if there is density contrast in it. In case of disperse flows the disperse phase self may act as a tracer. This gives rise to application of velocity measurement methods, which are based on correlation techniques. Adding liquid contrast agents to the continuous liquid phase is another choice. The paper introduces three methods of velocity measurements along with the associated data processing and gives some demonstration examples to discuss capabilities and limits of the methods.