| Numerical and experimental analyses of the structure of supersonic free-jet expansions of supercritical CO2 into the atmosphere and impacting on a flat plate are presented. Such expansions are important to technology used by chemical engineers in materials processing, known as the rapid expansion of supercritical solutions (RESS).; Numerical calculations for the axisymmetric, two-dimensional expansion are based on a time-dependent finite difference method known as the two-step predictor-corrector Lax-Wendroff technique, incorporating the Redlich-Kwong or Peng-Robinson equations of state to model supercritical CO2. A quasi-one-dimensional convergent-divergent nozzle approximation is also studied to test our numerical methods for the axisymmetric free-jet, to study the vibrational relaxation of CO2, and to study the clustering and condensation during the expansion.; Experimental mass flow rates for the free-jet expansion from two different types of sources (orifice and capillary) are studied and compared to one-dimensional numerical results. Optical shadowgraph measurements of the axisymmetric free-jet and associated shock wave structure are compared to the axisymmetric numerical results. Impact pressure and temperature along the flat plate are measured and compared to numerical results, as is a temperature probe of the free-jet expansion.; We find that the numerical methods are able to reproduce the flow rate and free-jet structure very well. The temperature and pressure profiles agree reasonably well, except for temperature along the impacted plate. The disagreement with temperature at the plate is due to neglect of heat transfer at the plate and, at higher pressures, to condensation in the expansion. Our results suggest that approximations based on ideal gases and quasi-one-dimensional flow analysis, often used by RESS researchers, may be useful for these supercritical fluid flows. The preliminary calculations and experiments indicate that condensation is important in these flows at high pressures, but it will require considerable further study to understand and predict the associated effects. |
