EFFECT OF WALL SHEAR STRESS ON DRAG REDUCTION OF VISCOELASTIC FLUIDS
WESTERN CO OF NORTH AMERICA RICHARDSON TX RESEARCH DIV
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Drag-reducing flow tests were carried out over a wide range of polymer concentrations in flow sections ranging from 0.18 inch to 6.0 inches in diameter. The water-soluble polymers used in this study were Separan AP-30, a highly efficient drag reducer, and J2-FP, a guar-type, lower molecular weight, moderately efficient drag reducer. It was found that the critical shear stress at the inception of drag reduction, was independent of flow-section diameter or boundary layer thickness. This critical shear stress was strongly dependent on polymer concentration for the highly efficient additive AP-30. For the moderately efficient J2-FP, only a very slight dependence of critical shear stress on additive concentration was found. For a given concentration of a specific polymer, the drag reduction was found to be a unique function of wall shear stress. The high molecular-weight polymer solutions were found to exhibit a decreased percentage of drag reduction at the higher shear rates which the lower molecular weight polymer solutions did not. This lower percentage was attributed to the mechanical scission of the high molecular weight polymer by shearing action of the fluid.
- Fluid Mechanics