Development of a nonequilibrium ECC mixing model for use in RELAP4/MOD7

The nonequilibrium mixing model, which interfaces with the existing homogeneous equilibrium calculational scheme used in RELAP4, is described in detail. Preliminary comparisons between code calculations using the mixing model and experimental data are presented for Westinghouse Electric cold leg ECC injection tests, Battelle Columbus Laboratories and Creare ECC bypass tests, and LOFT and Semiscale tests. These code--data comparisons indicate the need for consideration of nonequilibrium effects in code simulations of the ECC bypass refill phase of postulated LOCA transients. In addition, these results point out the need for continued development of constitutive relations for use in modeling steam water mixing phenomena

Modeling of CO2 Decompression across the Triple Point

The formation of significant quantities of solid CO2 as a result of surpassing its triple point during rapid decompression of CO2 pipelines employed as part of the carbon capture and sequestration (CCS) chain can present serious operational and safety challenges. In this paper, the development, testing and validation of a rigorous computational fluid dynamics (CFD) flow model for predicting solid CO2 formation during decompression is presented. Multiphase flow is modeled by assuming homogeneous equilibrium, and the pertinent thermodynamic data are computed using real-fluid equations of state. The flow model is validated against pressure and temperature data recorded during the decompression of an extensively instrumented 144 m long, 150 mm i.d. CO2 pipe initially at 5.25 °C and 153.3 bar. For the conditions tested, the simulated results indicate CO2 solid mass fractions as high as 35% at the rupture plane, whose magnitude gradually decreases with distance toward the pipe’s intact end

Validation of hyperbolic model for two-phase flow in conservative form

A mathematical formulation is proposed for the solution of equations governing isentropic gas-liquid flow. The model considered here is a two-fluid model type where the relative velocity between the two phases is implemented by a kinetic constitutive equation. Starting from the conservation of mass and momentum laws, a system of three differential equations is derived in a conservative form for the three principal variables, which are mixture density, mixture velocity and the relative velocity. The governing equations for the mixture offer the novel hyperbolic conservation laws for the description of two-phase flows without any conventional source terms in the momentum or relative velocity equations. The discretisation of the governing equations is based on splitting approach, which is specially designed to allow a straightforward extension to various numerical methods such as Godunov methods of centred-type. To verify the validity of the model, numerical results are presented and discussed. It is demonstrated that the proposed numerical methods have superior overall numerical accuracy among existing methods and models in the literature. The model correctly describes the formation of shocks and rarefactions for the solution of discontinuities in two-phase fluid flow problems, thus verifying the proposed mathematical and numerical investigations