Wall shear rate in the Taylor-Couette-Poiseuille flow at low axial Reynolds number

An experimental investigation was done by the use of visual observations and the electrochemical technique in order to study the appearance of hydrodynamic instabilities at low Re-axg in the gap between two coaxial cylinders, with radius ratio R-r/R-s = 0.615 and aspect ratio L/e = 24. A motor drove the inner cylinder and the outer cylinder was fixed. A Newtonian fluid (Emkarox HV45) and two non-Newtonian fluids (aqueous solutions of guar and CMC) have been used. The analysis of the evolution of the size of the Taylor vortices is carried out for Re-axg < 4.0. For Re-axg < 2 we showed that the vortices underwent a contraction phase up to Ta-g approximate to 80, and a stretching phase for Ta-g > 80. For higher Re-axg, the contraction phase vanished and the vortices progressively stretched with increasing Ta-g. A dimensionless representation was also proposed for wall friction generalized to non-Newtonian fluids following the Ostwald law. (C) 2002 Elsevier Science Ltd. All rights reserved.