Swirl driven solute mixing in narrow cylindrical channel

Abstract

We investigate the mixing of constituent components transported through a narrow fluidic cylindrical channel in a swirling flow environment. We solve for the flow field analytically using the separation of variables method under the framework of fully developed axial velocity and no-slip condition at fluid–solid interface and validate the same with numerical solution. The swirl velocity profile, which is a function of Reynolds number (Re), exhibits exponential decay along the length of the fluidic channel. We numerically solve the species transport equation for the Peclet number in the range of 102 to 104 coupled with the swirl velocity obtained for 0.1≤Re≤100, by using our in-house developed code essentially for the concentration distribution in the field. As seen, an increase in the Reynolds number results in complete rotation of fluids in the pathway, which, in turn, forms an engulfment flow (onset of chaotic convection) and enhances the underlying mixing efficiency substantially. The results show that inlet swirl promotes advection dominated mixing, while the dominance of advection increases substantially for the higher Reynolds number. We show that adding a small magnitude of swirl velocity at the inlet significantly reduces the channel length required for complete mixing even after the swirl velocity has decayed completely.