Flow Analysis for Wormlike Micellar Solutions in an Axisymmetric Capillary Channel

Flows of wormlike micellar solutions in an axisymmetric capillary channel were studied both numerically and experimentally. In the experimental study, velocity distribution measurements with a particle tracking velocimetry (PTV) were carried out using an aqueous solution of 0.03 mol/1 CTAB and 0.06 mol/1 NaSal as a test fluid. The velocity profile showed a plug-like shape and had inflection points where the velocity gradient rapidly changed. High shear rate regions near the channel walls spread with increasing the average velocity. In the numerical analysis, startup flows of the CTAB/NaSal solution were computed using a modified Bautista-Manero model as a constitutive equation. Startup flows at a constant average velocity U or at a constant average pressure gradient -L were numerically simulated. The numerical predictions of velocity profile at steady state agreed with corresponding experimental data. In the constant-U case, the velocity profile changes from Newton-like to plug-like with time. The inflection points in velocity profile appeared and moved towards the center-side with time. Temporal changes in both velocity gradient and fluidity suggested that the behavior in velocity related the shear-rate-jump property of wormlike micellar solution. In the constant-L case, the region of high shear rate and fluidity did not spread with time and their profiles temporally changed within this region.