Transient behavior near liquid-gas interface at supercritical pressure

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 µm for the liquid phase and 10-30 µm for the gas phase in 10-100 µs), 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.

Volume of Fluid method for low-Mach-number compressible supercritical liquid jet

“…Higher pressures enhance the dissolution of oxygen in the liquid phase and cause stronger variations in fluid properties across the mixing region. The direction of the interface displacement also matches the displacement predicted in [2]. At 10 bar, vaporization reduces the liquid volume (i.e., the interface recedes).…”

“…A one-dimensional configuration where an unperturbed liquid pool is sitting on a wall is analyzed. The qualitative behavior is in good agreement with [2], yet here the thermodynamic model has been improved, the interface is allowed to move and the momentum equation is solved. As the sharp initial condition relaxes, mass and heat diffuse in both phases.…”

“…This behavior has often been described as a very fast transition of the liquid phase to a supercritical gas-like state. But evidence of a two-phase behavior exists, whereby the liquidgas interface must be in local thermodynamic equilibrium (LTE) [2,3,4]. The failure to properly identify the two-phase problem in experimental setups is consistent with a fast atomization caused by the extreme thermodynamic environment.…”

Temporal atomization of a transcritical liquid n-decane jet into oxygen

“…Both fluids present similar properties near the liquid-gas interface, which is immersed in a variable-density layer and rapidly affected by turbulence [1][2][3][4][5][6][7]. Despite in the past being often described as a sudden transition from a liquid to a gas-like supercritical state [8,9], the requirement that liquid and gas be in local thermodynamic equilibrium (LTE) at the interface provides evidence that a two-phase behavior exists within a certain region of the mixture thermodynamic space [10][11][12][13][14][15]. For pressures above the fuel critical pressure, LTE enhances the dissolution of lighter gas species into the liquid fuel, which causes a local change in mixture critical properties.…”

“…For pressures above the fuel critical pressure, LTE enhances the dissolution of lighter gas species into the liquid fuel, which causes a local change in mixture critical properties. Moreover, mixing layers with large variations in the fluid properties develop in each phase [15].…”