UC Irvine

This thesis presents a numerical study of the heat and mass transfer occurring when a cool liquid is suddenly introduced to a hotter gas at supercritical pressures. Different binary mixtures of heavy hydrocarbons and light gases are considered and fluid properties are obtained using a real-gas equation of state and various high-pressure models. Liquid-gas interface dynamics and mass and thermal diffusion for different pressures are analyzed. Then, a comparison with expected growth rates of the Kelvin-Helmholtz (KH) instability is provided to learn whether a phase equilibrium is well established before hydrodynamic instabilities can become important.

Two phases may still appear at supercritical pressures because mixture critical properties differ considerably from pure species critical properties. The diffusion time scales in both phases are comparable to the KH instability transient (i.e., 20-100 microseconds). That is, diffusion layers of 10 microns thickness in the liquid and 30 microns in the gas are observed for the oxygen/n-decane mixture, suggesting that variations of fluid properties around the liquid-gas interface may affect breakup mechanisms. Furthermore, condensation by increasing pressure can be observed, even at supercritical pressures, while the First and Second Law of thermodynamics are obeyed.