Countercurrent flow limitation in a pressurizer surge line

In order to clarify the characteristics of countercurrent flow limitation (CCFL) in a pressurizer surge line, CCFL in a vertical pipe with a large diameter was evaluated using previous experimental data and a one-region model with an existing correlation of interfacial shear stress. The CCFL is defined by the relationship between the gas and liquid volumetric fluxes under a quasi-steady state after onset of flooding. A correlation for CCFL at the sharp-edged upper end of vertical pipes was constructed and it was compared to CCFL in the slightly inclined pipe. The comparison indicated that the liquid volumetric flux at the sharp-edged upper end was lower than that in a slightly inclined pipe when they have a large diameter such for an actual-scale pressurizer surge line. However, it was found that the liquid volumetric flux in integral experiments (including a slightly inclined pipe, a vertical elbow, and a vertical pipe) was lower than that in slightly inclined pipes and vertical pipes. Considering system characteristics from experimental data for the pressurizer surge line, it was concluded that the Kutateladze parameter should be applied with the slope of m = 0.94 and the constant of CK = 1.24 ± 0.1 for the Wallis type CCFL correlation.