Homogeneous two-phase flow models and accurate steam-water table look-up method for fast transient simulations

The accurate simulation of fast steam-water transients requires precise algorithms for calculating fluid properties. The system of the governing flow equations must be closed with an Equation of State (EoS) to calculate the pressure as a function of the system conservative variables. For water, accurate analytical EoS for this purpose are not available yet. The aim of this paper is to show an efficient and very accurate algorithm to calculate water properties when the independent variables of the EoS are the density and the specific internal energy. Our algorithm uses a new table look-up method with bicubic interpolation based on the IAPWS-IF97 EoS formulation, and it is able to account for metastable states. The liquid metastability domain is extended until the spinodal curve, here determined and compared with other formulations. The EoS algorithm is coupled to two classical homogeneous two-phase flow models, namely the Homogeneous Equilibrium Model (HEM) and the Homogeneous Relaxation Model (HRM). HEM and HRM are used to simulate fast depressurization, waterhammer and steam explosion problems. Comparison of the numerical results with available experimental data shows the good performance of the proposed algorithms.