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Hensel, F.; Prasser, H.-M.;
Positron Emission Tomography was used in a series of experiments in the field of two-phase flow systems. The main goal was to observe mixing and flow phenomena in efficient spatial and time resolution .
Liquid positron emitting tracers were used for monitoring the mixing of a tracer distribution in a bubbly flow. At the beginning of the experiment an aqueous solution of Sodium Fluorine (NaF), labelled with 18F is injected into the two-phase mixture at a certain local position. This tracer starts to disperse caused by turbulence. The radiation originating from the annihilation of the positrons is detected by two opposite detector arrays, a double head spherical PET-scanner . From the recorded event rates, a spatial intensity distribution of the annihilation events is calculated, which corresponds to the local concentration of the tracer.
For the experiments two setups were used. The fist consists of a flat rectangular water tank. Here the bubbly flow was generated by air injection near the tank bottom and by catalytic H2O2 decomposition, respectively. In the other setup, a vertical pipe was used. The bubbles were generated along a rod centred in the pipe, using catalytic H2O2 decomposition. In another experiment, the liquid drainage in a cellular foam was monitored.
The quantity of the active nuclide was restricted to several MBq, due to radiation protection requirements. Despite of this limitation, a good imaging is possible if the evaluation of event data can be restricted to two dimensions. For that case, a simple and time sparing midplane backprojection of the annihilation events can be applied. For the tracer, 18F was used in solution.
Using this technique, time sequences of images of the tracer concentration distribution with a time resolution of 0.5s were obtained and will be presented in the paper. This time base provides an appropriate statistical accuracy for the determination of the dispersion coefficients, too, which were determined for the bubbly flow and in the foam zone of the vertical pipe.
Transport processes in bubbly flows and foams seem to be interesting topics for investigation using a PET technique. The main advantage of PET tracers is the fact that many organic substances can be labelled with positron emitting isotopes which is important for the component sensitive investigation of many industrial processes, an objective of the further work.
Frontiers in industrial Process Tomography, Delft, April 9-12, 1997
Contribution to proceedings
Proceedings of the Conference Frontiers in Industrial Process Tomography II Delft, The Nederlands, April 9 - 12, 1997, pp. 47 - 51
Publ.-Id: 811 - Permalink