Acoustically Augmented Flow and Transport in Supercritical Fluids

Abstract

Acoustically augmented flow and transport in supercritical fluid (CO2) generated by standing wave in a cylindrical enclosure is simulated. The oscillatory flow field in the enclosure is created by the vibration of one of the end walls of the enclosure. A novel application of the acoustically augmented flow in membrane contactors used in supercritical fluid extraction process is demonstrated numerically. The predicted results from the present study can be utilized to enhance the transport mechanisms in these fluids. The geometric parameters and the frequency of the vibrating wall are chosen such that the lowest acoustic mode propagates along the enclosure. A real-fluid model for representing the thermo-physical and transport properties of the supercritical fluid is considered. The fully compressible form of the Navier–Stokes equations is used to model the flow fields and an implicit time-marching scheme is used to solve the equations. The formation of the acoustic field in the enclosure is computed and fully described and the acoustic boundary layer development is predicted. The interaction of the wave field with viscous effects and the formation of streaming structures are revealed by time-averaging the solutions over a given period. Due to diverging thermo-physical properties of supercritical fluid near the critical point, large scale oscillations are generated even for small sound field intensity. The effects of near-critical property variations and system pressure on the formation process of the streaming structures are also investigated.