Thermophysical flow simulations of rapid expansion of supercritical solutions (RESS)

Thermophysical flows of rapid expansion of supercritical solutions (RESS) were numerically simulated from the nozzle inlet to the outlet of the expansion chamber. In these studies, supercritical carbon dioxide (SCO₂) was used as the solvent, and naphthalene was used as the solute. Our approach seamlessly simulated SCO₂ entering the nozzle, SCO₂ crossing the critical pressure in the nozzle, CO₂ gas expanding into the expansion chamber, and CO₂ condensation in the chamber. The simulation is based on a preconditioning method developed by Yamamoto, together with mathematical models for thermophysical properties of substances in a program package for thermophysical properties of fluids (PROPATH). A primary issue was the extent to which changing the nozzle inlet and outlet pressures impacted the solubility of the solute. We also studied the effects of changing the nozzle throat diameter and throat length. In addition, we used a simple particle-formation model to predict nucleation, condensation, and coagulation of naphthalene particles. Our results indicate that the location at which the pressure crosses the critical pressure is sensitive to the pressure at the nozzle inlet, and nucleation of naphthalene starts near that location.