Transient Behavior near Liquid-Gas Interface at Supercritical Pressure

TL;DR

This study investigates the transient heat and mass transfer near a liquid-gas interface at supercritical pressures, revealing rapid establishment of phase equilibrium, formation of diffusion layers, and pressure-dependent mass flux reversal.

Contribution

It provides new insights into the transient behavior and phase dynamics at supercritical conditions, highlighting the pressure effects on vaporization and condensation processes.

Findings

Phase equilibrium is quickly established before hydrodynamic instabilities grow.

Diffusion layers form within microseconds, with thicknesses depending on pressure.

Mass flux across the interface reverses from vaporization to condensation as pressure increases.

Abstract

Numerical heat and mass transfer analysis of a configuration where a cool liquid hydrocarbon is suddenly introduced to a hotter gas at supercritical pressure shows that a well-defined phase equilibrium can be established before substantial growth of typical hydrodynamic instabilities. The equilibrium values at the interface quickly reach near-steady values. Sufficiently thick diffusion layers form quickly around the liquid-gas interface (e.g., 3-10 microns for the liquid phase and 10-30 microns for the gas phase in 10-100 microseconds), where density variations become increasingly important with pressure as mixing of species is enhanced. While the hydrocarbon vaporizes and the gas condenses for all analyzed pressures, the net mass flux across the interface reverses as pressure is increased, showing that a clear vaporization-driven problem at low pressures may present condensation at higher pressures. This is achieved while heat still conducts from gas to liquid. Analysis of fundamental thermodynamic laws on a fixed-mass element containing the diffusion layers proves the thermodynamic viability of the obtained results.