2017 Volume 45 Issue 2 Pages 125-132
Flow-induced orientational changes of xanthan gum aqueous solutions and hydroxypropyl cellulose aqueous solutions in a planar channel with an abrupt expansion were examined by measurements of the flow-induced birefringence changes and velocity fields along the centerline of the channel. Four kinds of the xanthan gum (X-gum, Mw >2,000,000) solutions with different concentrations (0.45 0.5 0.7 0.9 wt%) and two kinds of the hydroxypropyl cellulose solutions with different molecular weights (HPC-M, Mw = 620,000 / HPC-H, Mw = 910,000) were tested in this experiment. Characteristic times were evaluated from G' and G" curves respectively. The birefringence changes were delayed corresponding to the characteristic times. Typical sizes of regions where the flow structure of polymers were affected by the abrupt expansion were estimated with the birefringence changes. The normalized sizes have a good correlation with a viscoelastic factor (apparent Weissenberg number) estimated in upstream region regardless of the concentrations of the solutions nor the polymer types.
