# A Non-equilibrium Approach to Model Flash Dynamics with Interface Transport

## TL;DR

This paper develops a non-equilibrium thermodynamics-based modeling framework for liquid-vapor systems, capturing interface transport and stability properties through differential-algebraic equations.

## Contribution

It introduces a novel DAE-based model for non-equilibrium flash dynamics incorporating interface transport and stability analysis.

## Key findings

- The model is proven to be of index one.
- Equilibrium is unstable in non-isobaric regimes.
- Isobaric regimes are numerically shown to be stable.

## Abstract

This article presents a modeling framework for a class of multiphase chemical systems based on non-equilibrium thermodynamics. Compartmental modeling is used to establish the dynamic properties of liquid-vapor systems operating far from thermodynamic equilibrium. In addition to the bulk-phase molar/energetic dynamics, interface transport processes yield to algebraic constraints in the model description. The irreversible system is thus written as a system of Differential-Algebraic Equations (DAEs). The non-equilibrium liquid-vapor DAE system is proven to be of index one. A local stability analysis for the model shows that the equilibrium state is unstable for non-isobaric operation regimes, whereas numerical evidence shows that isobaric operation regimes are stable. To extend the stability analysis, internal entropy production for the irreversible flash-drum is presented as a Lyapunov function candidate.