Hydrodynamics modeling and analysis of rapid expansion systems of supercritical solutions (RESS)

Abstract

In this paper, we study the hydrodynamics aspects of the RESS (e.g. rapid expansion of supercritical solutions) process to produce fine particles for heat-sensitive organic compounds. The Computational Fluid Dynamic (CFD) modeling and analysis of the supercritical solutions passing through a capillary nozzle were studied. The CFD simulation is focused on the pre-expansion chamber of the RESS process consisting of three successive steps that are at the stagnation chamber (i.e. the reservoir), nozzle inlet and along the nozzle itself to the outlet. The solute considered is benzoic acid and the supercritical solvents are CO2 and CHF3 respectively. The aim of this study is to examinethe effect and sensitivity of the design parameters (i.e. temperature, pressure and density) on the formation of particulates in the chamber. The study reveals that at lower preexpansion temperature with constant pre-expansion pressure the solute nucleation seems to start inside the nozzle. Moreover, it is also found that pre-expansion pressure has insignificant effect on the nucleation process, i.e. the nucleation rate slightly increases when the pressure is set higher. Furthermore, the study also reveals that high preexpansion pressures and low pre-expansion temperature favors small particles. The results demonstrate that the variation of thee parameters in the ranges studied may lead to the increased super-saturation and simultaneously increase in nucleation rate.