Two-phase developing laminar mixing layer at supercritical pressures

TL;DR

This study numerically investigates a laminar shear layer at supercritical pressures, revealing phase equilibrium, property variations, and the transition from vaporization to condensation around 50 bar, with implications for continuum modeling.

Contribution

It provides detailed numerical analysis of phase behavior and property variations in supercritical shear layers, demonstrating the validity of boundary layer assumptions at high Reynolds numbers.

Findings

Phase equilibrium is established in supercritical shear layers.

Net vaporization occurs below 50 bar, condensation above.

Profiles collapse to similar solutions across different conditions.

Abstract

Numerical analysis of a shear layer between a cool liquid n-decane hydrocarbon and a hot oxygen gas at supercritical pressures shows that a well-defined phase equilibrium can be established. Variable properties are considered with the product of density and viscosity in the gas phase showing a nearly constant result within the laminar flow region with no instabilities. Sufficiently thick diffusion layers form around the liquid-gas interface to support the case of continuum theory and phase equilibrium. While molecules are exchanged for both species at all pressures, net mass flux across the interface shifts as pressure is increased. Net vaporization occurs for low pressures while net condensation occurs at higher pressures. For a mixture of n-decane and oxygen, the transition occurs around 50 bar. The equilibrium values at the interface quickly reach their downstream asymptotes. For all cases, profiles of diffusing-advecting quantities collapse to a similar solution (i.e., function of one independent variable). Validity of the boundary layer approximation and similarity are shown in both phases for Reynolds numbers greater than 239 at 150 bar. Results for other pressures are also taken at high Reynolds numbers. Thereby, the validity of the boundary layer approximation and similarity are expected. However, at very high pressures, the similar one-dimensional profiles vary for different problem constraints.