A hyperbolic phase-transition model coupled to tabulated EoS for two-phase flows in fast depressurizations

This article deals with a single-velocity six-equation two-phase flow model and its use for the simulation of metastable liquid–vapor flows of industrial interest like fast depressurizations in which phases are in thermo-chemical disequilibrium. The purpose of this work is to develop a numerical method of industrial grade with enhanced adherence to physics by employing advanced modeling techniques based on hyperbolic multiphase flow models proposed in the last two decades. The model here developed is able to accurately take into account disequilibrium between phases thanks to splitted relaxation processes for pressure, temperature and Gibbs free enthalpy disequilibria. At the same time, numerical calculations rely on fast and accurate Equations of State (EoS). To obtain such a tool, in this paper, we merge the single-velocity six-equation two-phase flow model with novel relaxation procedures and steam-water tables calculation methods. The outcome is an accurate and time-efficient hyperbolic model for simulating metastable two-phase flows. The merging builds up on previous work of the authors that was dedicated on the one hand to EoS-independent relaxation procedures for the six-equation model, and on the other hand on steam-water look-up table techniques coupled to simpler two-phase flow models. Since the single-velocity six-equation model is capable of accounting for vapor metastable states, the steam-water tables and the look-up table technique that we developed in previous work are extended here to the vapor metastable domain up to the vapor spinodal line. Then, the complete six-equation model is coupled to the new steam-water tables for the simulation of metastable two-phase flows occurring in the event of a fast depressurization. These simulations are validated against experimental data available in the literature. The final model is implemented in the EUROPLEXUS code for its use in nuclear reactor safety.