On The Existence, Formation and Stabilisation Of Lyne Vortices In Helically Coiled Reactors At Moderate Reynolds Numbers

Abstract

The occurrence of Dean and Lyne vortices in curved and coiled tubes is widely known. This paper is on the tracks of vortex structures in more resent helically coiled reactors, namely the Coiled-Flow-Reverser (CFR) and the Coiled-Flow-Inverter (CFI) (see top of figure 1). Time-resolved laser induced fluorescence (LIF) and time-resolved particle image velocimetry (TR-PIV) are used to characterize the existence of Lyne vortices in a range of Reynolds numbers from 500 to 2400 for single phase liquid-liquid mixing flows (see centre of figure 1). In this study parameters like the Reynolds number, the inlet angle and the geometry of the helically coiled reactor are varied and their influence on the vortex occurrence and the mixing coefficient is shown. The results are then compared to two-phase flow structures in helical pipes from Müller et al. (2021), in which secondary and tertiary vortices inside the liquid plugs exist as well. Two transition points for the formation of Lyne vortices in the CFI could be characterised. While Lyne instabilities occur in straight horizontal helix geometries at Reynolds numbers above 1000, in the CFI the first Lyne vortices formed at a Reynolds number of 560. From a Reynolds number of 1600 onwards, these begin to break off, whereby the Lyne vortices continue to occur continuously but no longer steadily. Pseudo-3D reconstructions of the flow in the CF and the CFI are used to show the flow behaviour and the occurrence of Lyne instabilities for different conditions.