The Effect of Bubble Size on the Radial Distribution of Void Fraction in Two-Phase Flow in a Circular Tube

Abstract

SIMMER-IV, a three-dimensional version of SIMMER-III, has been developed at JNC to study the safety of fast reactors mechanistically. SIMMER-IV was applied to the experimental analysis of bubbly flow to verify the models. The results of an experiment performed by Valukina et al. showed that the radial distribution of void fraction changes suddenly as the bubble size changes. In the present work, the analysis focuses on reproducing the change of the radial void distribution. The diffusion term, “lateral lift force,” and “wall force” were introduced in sequence into its momentum conservation equation. Naturally, the diffusion term improved the radial distribution of vertical velocity but did not explain the change of the radial void distribution in the experiment. Subsequent introduction of the lateral lift force increased the void fraction along the wall, but it did not change the radial void distribution as the bubble size changed. Finally, the wall force was introduced and, in accordance with the experimental results, the dependence of radial void distribution on the bubble size was proved. The behavior of a molten pool that is bubbly with steel steam plays an important role in the evaluation of LMFR severe accidents. This study is expected to improve the evaluation.