Flow regimes of free jets and falling films at high ambient pressure

Abstract

At atmospheric pressure the following flow regimes have already been reported for liquid free jets and falling films, that are “draining”, “dripping”, “Rayleigh disintegration”, “wavy disintegration” and “spray” for jet disintegration as well as “smooth film”, “waves”, “troughs” and “crests” for falling films, respectively. In a high-ambient-pressure environment there exists an additional falling film flow regime, i.e. “breakup into droplets”. At elevated pressures the viscosity of the liquid phase and the interfacial tension of the substances which are used decrease significantly due to dissolved carbon dioxide. In addition, the influence of the ambient gas-phase increases, so that the respective regimes occur at considerably lower liquid flow rates. In this work the conditions of the flow regimes have been studied and new own correlations have been developed. The results may be used for process development and reactor design in order to reduce the size of the apparatus or to generate surface area for mass transfer not by means of special contacting devices but by using atomization devices. Also, the formation of undesired aerosols can be avoided, which are almost impossible to remove and might be responsible for backmixing. As a sign for the strong interdependence of mass transfer and fluid dynamics it has been discovered that the flow patterns of saturated liquid free jets and falling films are clearly different from those of the corresponding undersaturated flows. This fact is especially important for scale-up of high-pressure reactors: exactly the same flow conditions have to be set in pilot and production column, e.g. to provide the required separation efficiency.