Ultrafast tomography for multiphase flow measurement in process applications


Ultrafast tomography for multiphase flow measurement in process applications

Hampel, U.; Fischer, F.; Bieberle, M.; Schubert, M.

The study of multiphase flows in process engineering requires sufficiently fast observation tools. Studies of hydrodynamics in bubble columns, fluidized beds, or mixing drums for instance, would enormously profit form cross-sectional or even volume imaging with at least 1000 frames per second speed. Unfortunately, optical techniques, such as high speed cameras and PIV, which are widely used to study transparent single phase flows, fail in multiphase flows due to their opaqueness. In the past electrical imaging techniques, such as electrical impedance tomography and wire mesh sensors, were frequently used for multiphase flow studies. But these techniques have some severe drawbacks. Thus electrical tomography has a very low spatial resolution. Wire mesh sensors are intrusive and cannot be used for particulate systems. Recently our group has introduced ultrafast electron beam X-ray tomography for multiphase flow studies. We developed the ROFEX scanner which is able to visualise different types of multiphase flows, such as gas-liquid or gas-particle systems, with scan rates up to 7000 frames per second, one millimetre spatial resolution and for cross-sections up to 120 mm diameter. The scanner utilizes electron beam technology. An electron beam of up to 150 keV energy is produced by an electron gun, focussed onto a semicircular X-ray production target and swept rapidly across the target by means of an electromagnetic deflection system. This way X-rays are generated from a fast moving focal spot. A fast detector inside the scanner head records the X-ray projection data which is subsequently reconstructed to cross-sectional images of the density distribution of the object of interest.
In an overview presentation we will discuss the applicability of this new imaging technology to different multiphase processes which are to be found in chemical and mechanical process engineering. The repertory includes hydrodynamics in pipes, bubble columns, stirred tanks, powder mixing drums, monoliths, foams, fixed beds, fluidized beds, and corrugated sheets of destillation packings. The presentation will address measuring accuracy with respect to disperse and separated flows, limits of the methods and implications for process optimization and CFD code development.

Keywords: Electron beam tomography; X-ray tomography; flow measurement; two-phase flow

  • Lecture (Conference)
    10th Conference on Gas-Liquid and Gas-Liquid-Solid Reactor Engineering, 26.-30.06.2011, Braga, Portugal

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Publ.-Id: 17599