Residence time distribution in twisted pipe flows: helically coiled system and chaotic system

 This study compares residence time distributions in a helically coiled tube and a spatially chaotic system. The chaotic system consists of an array of bends, the plane of curvature of each one makes a 90° angle with that of its neighbors. Chaotic trajectories are obtained by the switch in the symmetry plane of the Dean vortices which appear in the bends. Mixing in the two configurations is compared by modeling the residence time distributions, experimentally determined by means of a two-measurement-point technique, using the axial dispersion plug-flow model. For Reynolds numbers greater than 2500, axial dispersion in the chaotic system is more than 20% less than in a helically coiled tube having the same number of bends. The decrease in axial dispersion is due to the generation of chaotic trajectories, which also contribute to an increase in transverse dispersion. Thus, the chaotic curved pipes system appears very promising in producing good mixing, especially in a laminar flow regime. Received: 4 June 1996 / Accepted: 23 October 1996