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Comparison of countercurrent flow limitation experiments performed in two different models of the hot leg of a PWR with rectangular cross-section

Vallée, C.; Seidel, T.; Lucas, D.; Tomiyama, A.; Murase, M.

In order to investigate the two-phase flow behaviour during counter-current flow limitation in the hot leg of a pressurised water reactor, two test models of were built: one at the Kobe University and the other at the TOPFLOW test facility of Forschungszentrum Dresden-Rossendorf (FZD). Both test facilities are devoted to optical measurement techniques, therefore, a flat hot leg test section design was chosen. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux condenser cooling mode appearing in some accident scenarios. The fluids used were air and water, both at room temperature. The pressure conditions were varied from atmospheric in Kobe to 3.0 bar absolute at TOPFLOW. According to the presented review of the literature, very few data is available on flooding in channels with rectangular cross-section, and no experiments were performed in the past in such rectangular models of a hot leg. Usually, the macroscopic effects of CCFL are represented in a flooding diagram, where the gas flow rate is plotted versus the discharge water flow rate. Commonly, the non-dimensional superficial velocity (also known as Wallis parameter) is used to plot the flooding diagram. However, the classical definition of the Wallis parameter contains the pipe diameter as characteristic length, which was originally defined by Wallis (1961) for counter-current flow limitation in vertical pipes and not in near horizontal channels with rectangular cross-section. In order to be able to perform comparisons with pipe experiments and to extrapolate to the power plant scale, the appropriated characteristic length should be determined.

Because the experimental projects on this subject at the Kobe University and at FZD were launched independently, a detailed comparison of both test facilities is presented. With respect to the CCFL behaviour, it is shown that the essential parts of the two hot leg test sections are very similar. This geometrical analogy allows to perform meaningful comparisons. However, clear differences concerning the dimensions of the cross-section (H x W = 150 x 10 mm² in Kobe, 250 x 50 mm² at FZD) allow to point out the right characteristic length for hot leg models with rectangular cross-sections. The hydraulic diameter, the channel height and the Laplace critical wavelength (leading to the Kutateladze number) were tested. The experimental results obtained on both test facilities show clearly that the channel height is the suited characteristic length. Finally, the experimental results are compared with similar experiments and empirical correlations for pipes available in the literature. In spite of the scatter of the data and of the different correlations, the overall agreement is good.

Keywords: two-phase flow; flooding; counter-current flow limitation; hot leg; pressurised water reactor; Wallis parameter; rectangular channel

  • Contribution to proceedings
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China, Paper ICONE18-30089
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering (ICONE18), 17.-21.05.2010, Xi'an, China
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 133(2011)5, 052917
    DOI: 10.1115/1.4002884
    Cited 16 times in Scopus

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