Experimental investigations of flow patterns and pressure gradients of oil/water flow with and without drag-reducing polymer (DRP) were carried out in horizontal and upward-inclined acrylic pipe of 30.6-mm inner diameter (ID). The oil/water flow conditions of 0.1- to 1.6-m/s mixture velocities and 0.05-0.9 input oilvolume fractions were used, and 2,000 ppm master solution of the water-soluble DRP was prepared and injected at controlled flow rates to provide 40 ppm of the DRP in the water phase at the test section. The flow patterns at the water-continuous flows were affected by the DRP, whereas there were no tangible effects of the DRP at the oil-continuous flow regions. The upward inclinations shifted the boundaries between stratified flows and dual continuous flows, and the boundaries between dual continuous flows and water-continuous flows to lower mixture velocities. This means that the inclinations increased the rate of dispersions. The frictional pressure gradients for both with and without DRP slightly decreased with inclinations especially at low mixture velocities, whereas the significant increases in the total pressure gradients with the inclinations were more pronounced at low mixture velocities. The inclinations did not have a major effect on the drag reductions by the DRP at the high mixture velocities and lowinput oil-volume fractions where the highest drag reductions recorded were 64% at 0° inclination and 62% at both + 5° and + 10° inclinations. However, the inclinations increased the drag reductions as the input oil-volume fractions were increased before phase-inversion points.
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