Dilute Polymer Solution Flows Through Periodically Constricted Tubes

Abstract

The results of experiments on the drag of dilute Polyox solution flows in tubes with periodic step change in diameter are presented. Constricted parts of tubes have 0.8, 1.85 and 4.15 mm i.d. Large to small inner diameter ratio for the tube is 2.5, In addition to tubes, transparent periodically constricted ducts with square cross section were tested. Several different concentrations up to 200 ppm were used.

Significant drag increase was observed. For some concentrations and flow rates ratio of Polyox solution friction to Newtonian was found as high as 20. The maximum drag increase asymptotes were noted. It was showen that in some cases pressure drop for Polyox solution flow falls abruptly with increase of flow rate.

Connection of anomalous drag increase with a flow instability (elastic turbulence) was shown by visualisation and laser Doppler measurements in transparent ducts. The results were compared with well known results for polymer solution flows in porous media.

Diagrams of flow type in coordinates Reynolds number-Weissenberg number were introduced. Flow in nonuniform tubes and flows in uniform tubes were analyzed on the basis of these diagrams. The analog between the jump of pressure drop in nonuniform tube flow and the onset of the Toms phenomenon is discussed.