Abstract
Mixing behaviors in a conical Taylor–Couette flow system were investigated at low Reynolds numbers using flow-visualization and salt-solution tracer techniques. Owing to sensitivity during the start-up procedure, the acceleration rate of the inner conical cylinder was precisely controlled by computer. Two different flow modes were observed in the laminar flow regime. When the inner conical cylinder was accelerated at a low rate (0.05 rad/s2), the whole fluid column was filled with helical vortices. In the case of a high acceleration rate (0.5 rad/s2), an upward traveling motion of the Taylor vortices was observed. The vortices started to display a global upward motion due to the strong meridional circulation. These two flow modes showed quite different mixing behaviors even at nearly equal Reynolds numbers. In the case of the upward traveling motion, the tracer substance was convected with the traveling vortices in the main flow cross-section and with the meridional flow at the outer-edge cell boundaries. In the helical motion, on the other hand, the tracer was transported by diffusion-like motion along the helical vortex filament and by convection along the secondary flow streamlines at outer-edge cell boundaries.
