An optimized delayed equilibrium model for predicting the pressure profile of the critical flow in a slit

Abstract

The mass flux and pressure profile of the critical flow in a slit are connected to the original diameter and concentration of radioactive aerosols in leak-before-break monitoring in nuclear power plants. The Delayed Equilibrium Model (DEM), although accurate for mass flux and pressure prediction of critical flow in a circular tube, suffers from underprediction of the pressure drop for critical flow in the slit. In this study, an optimized DEM considering the shape effect of flash boiling is proposed by changing the saturated phase mass flow rate fraction gradient and two-phase friction coefficient multiplier in the DEM. Two novel equations for the new coefficients, C4 and C5, are introduced in the optimization. The relative error of the critical flow pressure in the slit can be reduced using the optimized DEM. In addition, a sensitivity analysis of the original critical flow model is conducted and the mass flux and critical pressure of the critical flow model are found to be most sensitive to the inlet temperature. The effectiveness of the optimization proves that the shape effect of the velocity of achieving thermal equilibrium in flash boiling is critical for the critical flow in a slit.