NUMERICAL-SIMULATION OF RAPID EXPANSION OF SUPERCRITICAL-FLUID

The expansion of a supercritical fluid solution through a nozzle is th e key to one approach for producing microscale particles. It is based on the hyper-compressibility and the change of the solution capacity o f the fluid from supercritical fluid conditions (high pressure) in exp ansion to a lower pressure environment. Simulation of the flow needs a good approximation of the Riemann problem to this type of fluid, and an accurate representation of the supercritical state by a suitable Eq uation of State (EOS), the integration of the equations of the motion is performed with the implicit TVD scheme of Harten and Yee and solved with the Alternating Direction (ADI) method. Comparison with several test problems is given. It shows the reliability of the scheme for cap turing shock waves and rarefaction waves, for representing the gradien ts of different variables in the nozzle and the jet, compression and e xpansion phenomena in the jet, and behaviour of the flow near the crit ical region.