A MOLECULAR VISCOELASTICITY INTERPRETATION OF THE WALL SHEAR STRESS THRESHOLD IN THE TOMS EFFECT,
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF AERONAUTICAL ENGINEERING
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The turbulent-flow friction reduction produced by very low concentrations of linear macromolecules in good solvents was shown by Virk and by Elata and Tirosh to occur only when the pipe wall shear stress exceeds a particular threshold value for each polymer. A viscoelastic hypothesis is suggested in which the threshold corresponds to a viscoelastic dispersion like that which is theoretically and experimentally found for dilute solutions subjected to oscillatory shear about zero mean shear rate. A preliminary comparison with experiment for unfractionated polyethylene oxide show that the order of magnitude of the shear stress threshold value is predicted correctly.