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High-Resolution X-ray Tomography
for Nuclear Applications and Research
 
High-Resolution Cone Beam Tomography for Two-Phase Flow Diagnostics

With the acquired knowledge of the geometrical and density accuracy, the cone beam prototype tomograph was used to determine the gas distribution in actual bubbly flow. The main goal of these measurements was to analyze a few known patterns in comparison with previous X-ray tomography studies [e.g. Cherdron 1998].

Here we present a typical example of upward bubbly flow. For the upward flow example the main interest was to generate a wallpeaked gas distribution and to determine its characteristics with the improved geometrical resolution of the present instrument.

Thus, for a symmetrical injection with one central nozzle of a volumetric gas fraction b=3.25% and a superficial liquid velocity j1= 1.8 m/s, one notices an unexpectedly sharp wallpeaked distribution.

Gas distribution in upward bubbly flow: symmetrical injection through one central nozzle
b=3.25%, j1=1.8 m/s, Height = 40D
This figure shows several slices through
the 3D gas distribution for the flow analyzed above
Ultra fast X-Ray Computed Tomography for Transient Phenomena
Two-phase flow measurements

The measuring plane was set at 0.72 m from the air-water mixer exit. Bubbly flow was attained by injecting air through a sintered mesh plate with 100 microns pores, while air was introduced through four 5 mm diameter nozzles.
As the air flow rate increases the inner flow pattern becomes invisible. However, we detected a concentration of bubbles inside the bubble swarm as the air flow rate increases.

Using image processing techniques, area and perimeter of each bubble can be counted. The area ratio of air and water in the cross section represents the void fraction, while the perimeter does the interface length. The perimeter determined here is normalized by the inner perimeter of the pipe. This parameter is an indicator of how much the bubble surface is deformed. The deformation of the slug bubble interface, especially in the wake region was significant under the present flow conditions and contributed to an increase in the interface area.

(1.0sec., jg=0.30m/s) (1.0sec., jg=0.30m/s)
Instantaneous bubble interface visualized by ultra fast X-ray CT for different flow patterns corresponding to four combinations of liquid and gas superficial velocities.
Time-resolved void fraction and normalized interface length for a slug flow pattern.
jg=0.385m/s, j1=0.621m/s  
Fluidized bed measurements  
Fast X-ray CT is suitable for visualization of voids in the alumina powder since the effective density is lower than that of water. To obtain the interface area quantitatively, we used a fast-scanning X-ray CT that scans a crosssection of a flow channel in less than 4 ms and visualizes the instantaneous, two-dimensional phase distribution in a vertical upward slug flow.
jg=0.04m/s jg=0.07m/s
Pseudo-3D representation of gas flow in alumina powder
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