Drag reduction in pipe flows with polymer additives

Polyethylene Oxides (PEO) with molecular weights of 4 and 6 million and a Polyacrylamide (PAM) with a molecular weight of 15 million, were added to a turbulent pipe flow (15000 \u3c Re \u3c 50000) for drag reduction. The polymer was injected directly into the test section in one scenario, premixed in a tank and then pumped through the test section in the second. The injection addition method was found to be optimal because it subjected the polymer to lower amounts of shear stresses than the premixed addition method. A maximum of 75% reduction in drag was obtained. Even trace concentrations, as low as 2.5 WPPM (weight parts per million) , resulted in as high as 37% reduction in drag. Long thin high molecular weight polymers (PEO) were more effective than coiled high molecular weight polymer (PAM) . For the same molecular structure it was found that the polymer with heavier molecules had better drag reducing characteristics. The polymer with coiled molecules, however, is more resistant to shear stresses which break down the polymer into smaller less effective molecules. It was found that there is a critical concentration for the greatest drag reduction. This concentration is approximately 375 WPPM (.0375% byweight) of PEO for the injection method, and 500 WPPM of PEO for the premixed method. At greater concentrations, the viscosity of the solution increases such that the drag reduction characteristics of the polymer can no longer compensate