Identification and classification of the flow pattern of hydrogen-air-steam mixture gas under steam condensation.

Under the severe accident of the nuclear reactor, the strong coupling phenomenon exists between the transport and condensation of the steam-air-hydrogen multi-component gas in the containment atmosphere. Under this coupling effect, the flow patterns of mixture gas induced by condensation are critical to hydrogen accumulation risk assessment. The general flow characteristics of typical flow patterns were qualitatively predicted and confirmed in our previous work. However, the transient mass transfer process of multicomponent gases is complex, and flow pattern transitions are difficult to be captured. To further clarify these contents, experiments and corresponding numerical simulations are combined in the present work. The formation mechanism of the typical flow patterns is further revealed. The flow pattern transition boundaries of the mixture are quantified based on more data in confirmatory experiments. Experiments are performed under wider wall sub-cooling (Δ T = 60–110 °C) and wider range of steam concentration (X steam) from 16% to 90%, the volume concentration of helium in non-condensable gases (X He / X Non) ranges from 10% to 70%. Results show that the homogeneous downward flow is generally formed when X He / X Non < 40%. Under medium helium concentration (X He / X Non : 42%–55%), when X steam > 30%, the flow pattern of the mixture gas is the separation flow. Under high helium concentration (X He / X Non > 55%), the flow pattern of the mixture gas is the homogeneous upward flow when X steam > 20%. Furthermore, the empirical component correlations to classify the three flow patterns are proposed for the first time. Correlations and numerical simulation have good consistency in the prediction of flow patterns under most component conditions. • Transient mass transfer of multicomponent gases induced by condensation is discussed. • The formation mechanism of the typical flow patterns is further revealed. • Flow pattern transition boundaries of the mixture gas are quantified based on test. • Empirical component correlations to classify the typical flow patterns are proposed. • Correlations and numerical simulation results have good consistency. [ABSTRACT FROM AUTHOR]