  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.
