Paramètres géométriques de contrôle de la détente d'un fluide supercritique

Pursuing the work initiated by Ksibi et al. [European J. Mech. B/Fluids 15 (1996) 569], where the simulation of the RESS of CO2 through the nozzle with small diameter was considered, we present here a numerical contribution to investigate the influence of the geometrical characteristics of the nozzle on the jet hydrodynamics of the CO2, initially at a supercritical state. As the nucleation and the growth of the micro-scale particles depend on the flow behavior inside and downstream of the nozzle, the main issue of this work is to draw some conclusions on what design of the nozzle is the most favorable for the RESS process. The numerical procedure is based on the resolution of the Navier-Stokes equations coupled with the Altunin and Gadetskii equation of state. Following the temporal evolution of the velocity field, we can evaluate the transient time needed to reach the permanent regime. The numerical results show the existence of a Mach stem and successive sharp recompressions within the core of the jet. We show that the Mach stem location and the flow structure depend on both the nozzle inlet and outlet thermodynamic conditions and the nozzle geometry. Computing the jet flow through several capillaries shows that the pressure distribution during the expansion of the supercritical fluid is a function of the nozzle length and diameter.