Dr. Frank Barthel
Experimental Thermal Fluid Dynamics
Phone: +49 351 260 - 2348, 3704
Fax: +49 351 260 - 12348

Ultrafast electron beam X-ray tomography system "ROFEX"

In many technical facilities from energy production and chemical industry the knowledge about the structure of the inherent multiphase flows is of great interest. The ultrafast X-ray tomograph “ROFEX” (Rossendorf Fast Electron beam X-ray tomograph), which has been developed at the Helmholtz-Zentrum Dresden-Rossendorf, is a powerful, noninvasive imaging tool for this purpose. The device has been especially designed for measurements at the vertical test section DN50 of the experimental facility TOPFLOW. Due to its versatility the system is further applicable to a variety of other objects from fluid dynamics and chemical engineering up to a diameter of 120 mm. So far, frame rates of up to 7000 cross-sectional images per second at a spatial resolution of about 1 mm have been reached.


Measurement principle

For the acquisition of projections from different viewing angles, which is essential for computed tomography, this technique does not employ rotating objects or source-detector compounds. Instead, an electron beam is focused on a circular tungsten target and at the same time periodically deflected with high frequency in order to generate a moving focal spot on the target and thus an X-ray source rotating around the object. This source irradiates the object from different viewing angles. A static detector ring surrounding the object measures the radiation passing the object at a high frequency and synchronized with the beam deflection. From the projection data set of one revolution of the electron beam a non-superimposed cross-sectional image of the density distribution within the object can be reconstructed. The images can then be used to extract, for example, phase boundaries or gas fractions.

MN ROFEX_principle

TOPFLOW experiments

The ultrafast X-ray tomograph ROFEX was primarily developed for non-intrusive measurements of phase distributions within water-air and water-steam two-phase flows in the test section DN50 of the experimental facility TOPFLOW. For this purpose, an elevator system has been installed at the test section, which allows vertical positioning of the tomograph within a range of four meters. Thus, the complete evolution of the flow within the pipe can be studied by measuring in different heights. A specially designed variable gas injection unit can be mounted either at the upper or at the lower end of the test section to study both upward and downward directed flows.


Ultrafast X-ray tomograph ROFEX at
the vertical test section DN50 of the
TOPFLOW facility


ROFEX with radiation
protection housing in the upper
measurement position


variable Gaseinspeisung

Variable gas injection unit
for the test section DN50




Interesting details from time sequences (axial cuts) of visualized two-phase flows:

a) bubble cluster in the wake of a large bubble

b) liquid lamellae separating large bubbles

c) single gas bubble in water hose between two bubbles

d) water drops in a large gas bubble

Further applications

The ultrafast X-ray tomograph ROFEX is applicable to a variety of dynamic processes, whose inner structure should be visualized non-intrusively with high temporal resolution. Beside multiphase flows in industrial plants, reaction processes in chemical engineering as well as online quality inspection are among the main fields of application.


Tomography of falling  walnuts
(dynamic quality inspection)


Tomography of falling peperoni hull
(dynamic quality inspection)






Tomography of a fluidized bed
(Column diameter 100 mm)

Liquid distribution at the flooding point
in a Mellapak® structured packing

Two-plane tomography

At the moment, the ultrafast X-ray tomograph ROFEX is extended by a second tomography plane consisting of target and detector ring. In this way, not only phase distributions within the flow but also velocities can be measured. This is an important gain in information, because bubble sizes can be determined more accurately with known gas phase velocity and thus prove to be valuable for the validation of CFD models.



Dr. Frank Barthel
Experimental Thermal Fluid Dynamics
Phone: +49 351 260 - 2348, 3704
Fax: +49 351 260 - 12348