Tomographic imaging for multiphase flows

Multiphase flows are a common phenomenon in many processes and systems in the chemical and mineral oil industry. Those flows occur in many different forms such as disperse gas-liquid flows in bubble column reactors, gas-solid flows in fluidized-beds or bubble-, splash- and film flows in distillation systems. Due to their nature, they are difficult to record by means of standard measurement techniques, challenging to characterize theoretically and complex to model numerically. In order to monitor and characterize those flows in industrial systems as well as in research facilities it is necessary to apply methods with the ability to measure the phase distribution, phase interface density, turbulence- and velocity parameters in continuum phases and also the thermal-, material- and impulse transports between the different phases with high spatial and temporal resolution. Because in many cases multiphase flows are opaque, the application of common optical measurement principles is limited. In addition, industrial processes run at high pressure and temperature in vessels with thick metal walls. This limits the means of instrumentation and demands for robust measurement equipment.
In the recent past, the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has undertaken great efforts in the development of tomographic imaging principles that allow the understanding of multiphase flows with high spatial and temporal resolution. Some results of these developments, like the wire-mesh-sensors, the gamma ray computed tomography and the ultrafast X-ray computed tomography will be presented in the talk. With the wire mesh sensor, it was possible to analyze transient gas liquid flows with frame rates up to 10,000 pictures per seconds and a spatial resolution of 2 mm for the first time. The gamma ray computed tomography allows the investigation on high-pressure instruments and facilities with a spatial resolution of 2 mm. Finally, the Ultrafast X-ray computed tomography combines various positive features, such as contactless measurement with high spatial (~ 1 mm) and temporal (~ 10,000 frames per second) resolution as well as the visualization of opaque and solids-bearing flows. The talk introduces the described measurement technologies regarding their physical and technological principle and provides an insight into potential applications and methods for image data analysis.