The flow of dilute aqueous solutions of macromolecules in various geometries. II. Straight pipes of circular cross-section

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Abstract
For pt.I see ibid., vol.9, no.5, p.721 (1976). The effect of traces of macromolecular additives on the stability of laminar flow has been studied in pipes of radii 0.85, 0.88, 1.60, 2.00, 2.20, 2.70, and 3.00 mm at temperatures ranging from 15-35 degrees C. Drag reduction in fully-developed turbulence and pressure fluctuations during the transition from laminar to turbulent flow have also been studied. Most experiments have been done with 250 ppm polyacrylamide solutions. Drag reduction occurred whether or not the stability was affected, the amount increasing the decreasing pipe diameter. Both the amount of destabilization (or stabilization as the case may be) and the amount of drag reduction decreased as the temperature was increased. It might be concluded that the factors affecting drag also affected the stability. Pressure fluctuations were least in the solution when the flow was destabilized and most when it was stabilized. A phenomenological theory involving known molecular properties is put forward to account for the results.