Numerical Study of the Effect of a Power-law Fluid Flow Structures on Levels of Mixing in a Taylor Couette Configuration

Abstract

This work is a numerical study on the effects of the flow structures of the power-law fluid between two concentric cylinders with an upward laminar axial flow on levels of mixing and mean residence time through the Taylor Couette system. The cylindrical annular duct presents a radius ratio of 0.5 and an aspect ratio of 8. The inner cylinder is rotating while the outer one is kept at rest. The residence time distributions (R.T.D.) method and the mean residence time (Tm) are used to determine the number of tanks in series and the dispersion coefficient to evaluate levels of mixing. To this end, a pulsed input injection of a tracer is computing at the outlet of the annulus. As a main objective of this study, is to analyze the effect of the flow structure of a power-law fluid between two concentric cylinders on the mixing level and mean residence time in a Taylor Couette system. The novelty of our work is the use of power-law fluids as particles-carrying fluids. Several parameters, such as the axial Reynolds number (Re), the Taylor number (Ta), and the power-law index behavior (n), are used to show their impact on levels of mixing. It is shown that when n increases, the number of stirred tanks in series N increases for pseudoplastic fluids (n<1), indicating low levels of mixing while the parameter (N) decreases for dilatants fluids (n>1), revealing high levels of mixing. The increase of the power-law index in the range of 0.6<n<1 decreases the dispersion coefficient, indicating the non-ideal mixing in the duct. In addition, for further increase of the power-law index in the range of n>1 increases the dispersion coefficient points to the well-mixing.