Three-dimensional flow pattern visualization and bubble size distributions in stationary and transient upward flashing flow

• Published in: International journal of multiphase flow 2006-08, Vol.32 (8), p.996-1016
• Main Authors: Manera, A., Prasser, H.-M., Lucas, D., van der Hagen, T.H.J.J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Bubble size; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Flashing; Installations for energy generation and conversion: thermal and electrical energy; Three-dimensional visualization; Two-phase flow
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/j.ijmultiphaseflow.2006.03.005

For the first time, an experimental three-dimensional reconstruction and visualization of stationary and transient flashing flow in a vertical pipe (47 mm diameter) is presented. The measurements have been performed by means of wire-mesh sensors. This type of sensor delivers two-dimensional void-fraction distributions in the pipe cross-section where it is mounted with a maximum sampling rate of 10,000 frames per second. A sampling rate of 1200 frames per second has been used in this work. Steam bubbles have been identified from the wire-mesh data and their complete three-dimensional reconstruction has been performed by taking into account the steam bubble velocity. For the estimation of the bubble velocity, two wire-mesh sensors positioned at a small axial distance from each other have been used. The velocity has been determined by cross-correlation of the two wire-mesh signals, by direct identification of the traveling time of the steam bubbles between the two sensors and by means of a drift-flux model. A comparison between the three methods of bubbles velocity measurement is reported. Stationary and time-dependent bubble size distributions have been derived. The stationary radial void-fraction profiles have been decomposed according to bubble size classes and compared with the results obtained with an equilibrium model.