A new temperature evolution equation that enforces thermodynamic vapour-liquid equilibrium in multiphase flows -- application to CO2 modeling

TL;DR

This paper introduces a simplified and efficient numerical framework for simulating CO2 depressurization, featuring a novel single-equation vapor-liquid equilibrium model and an integrated ODE for thermodynamic consistency.

Contribution

It proposes a new single-equation VLE model and an ODE derived from the UV-Flash equation, enhancing computational efficiency in multiphase CO2 flow simulations.

Findings

Reduced computational cost compared to traditional methods

Efficient solution of coupled flow and thermodynamics equations

Validated approach for depressurization scenarios

Abstract

This work presents a novel framework for numerically simulating the depressurization of tanks and pipelines containing carbon dioxide (CO2). The framework focuses on efficient solution strategies for the coupled system of fluid flow equations and thermodynamic constraints. A key contribution lies in proposing a new set of equations for phase equilibrium calculations which simplifies the traditional vapor-liquid equilibrium (VLE) calculations for two-phase CO2 mixtures. The first major novelty resides in the reduction of the conventional four-equation VLE system to a single equation, enabling efficient solution using a non-linear solver. This significantly reduces computational cost compared to traditional methods. Furthermore, a second novelty is introduced by deriving an ordinary differential equation (ODE) directly from the UV-Flash equation. This ODE can be integrated alongside the governing fluid flow equations, offering a computationally efficient approach for simulating depressurization processes.