DRAG REDUCTION BY DILUTE POLYMER SOLUTIONS IN TURBULENT FLOW.
NAVAL RESEARCH LAB WASHINGTON D C
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The mechanism by which water-soluble polymers reduce hydrodynamic drag on solid surfaces was investigated by measurements of flow birefringence and of turbulent flow in pipes. Flow birefringence and flow field orientation of Polyox polymers in the molecular weight range from 200,000 to 6,000,000 showed that Polyox macromolecules continue to deform with increasing velocity gradient even after alignment with the flow field at gradients in excess of 2000sec. All solutions used were found to be Newtonian, with the exception of the AcrysolA-5 solutions. The flow data for Polyox solutions in a Pyrex pipe were examined in terms of Meyers fluid property parameter and Elatas relaxation time hypothesis for the initiation of drag reduction. It was found that drag reduction in the Pyrex pipe was initiated at a value of the order of one-fifth that predicted by Elatas theory. Moreover, added salt the solution being 0.3 molar in K2SO4 had no effect on the flow of Polyox Coagulant solutions even though the intrinsic viscosity upon which Rouse relaxation times depend was cut to slightly more than one-third of its value in the pure solvent. The unusually high values of Meyers fluid property parameter observed at low concentrations suggests that adsorption on the Pyrex pipe walls may be playing a role in drag reduction. Author
- Fluid Mechanics