EXPERIMENTAL STUDIES ON THE TAYLOR-COUETTE FLOW OF SHEAR-THINNING FLUIDS
Two concentric cylinders with the inner cylinder rotating cause circumferential flow with a Taylor vortex under a certain range of Reynolds numbers. This is called Taylor–Couette flow. It has been the focus of extensive study in terms of Newtonian fluids but not non-Newtonian fluids. Despite various industrial applications, the flow transition mechanism of the flow remains unclear. Therefore, many kinds of apparatuses using Taylor–Couette flow in the redesign and scale-up are still under investigation. The objective of the present study is first to determine the transition points of Taylor-vortex flow and the wavy vortex flow regime with a non-Newtonian working fluid. To understand the effect of the working fluid, two kinds of shear-thinning liquids with different structural viscosity indices were compared. Particle image velocimetry (PIV) was used as the flow visualization technique for a wide range of Reynolds numbers. A water solution of guar gum resulted in a stable six-cell mode in the Taylor-vortex flow and wavy-vortex flow regimes. The other working fluid, with xanthan gum, resulted in a vertically enlarged oval vortex that appeared under the same Reynolds number range. Both results were significantly different from the flow with Newtonian working fluid. In conclusion, we confirm that the shear-thinning characteristics of the working fluid affect the aspect ratio of the edge vortex as well as the drifting of the vortex center along the axis of the cylinder.