Two-Phase Flow of CO2 with Phase Transfer

A model for two-phase pipeline flow of CO2 with phase transfer is presented. Two different relaxation models for phase transfer are developed. The system of equations is solved by splitting it into a hyperbolic conservation law and a relaxation ODE, solved by a multi-stage (MUSTA) finite volume scheme and the backward Euler method, respectively. The stiffened-gas equation of state is used for calculating thermodynamic properties. Simulation results from a depressurisation case of a CO2 pipe, causing phase change and cooling, are presented, showing that statistical rate theory predicts solutions close to those of an equilibrium model with instant phase transfer.