Paul Onubi Ayegba &
This study investigates the effect of U-bend on polymer drag reduction (DR) and flow patterns for oil-water flows. The test section consisted of 19-mm ID clear polyvinyl chloride (CPVC) straight pipes and U-bend (R = 100 mm). Measurements were carried out under different flow conditions at hydrodynamically developed flow section before the bend, in the bend and at two redeveloping flow sections after the bend. Observed flow patterns at various test sections were similar though mixture velocities at transition sometimes varied between the test sections. In general, the addition of polymer imposed partial or complete flow stratification. Pressure losses differed at the various test sections and this difference was strongly related to the superficial velocity of the phases and flow patterns. DR at all test sections generally increased with water superficial velocity and reduced with oil fraction in the region of strong turbulence. At high mixture velocities, DR upstream of the bend was highest while the least was recorded at the bend. A reverse behaviour was recorded at low mixture velocities. The highest DR upstream of the bend, in the U-bend and at the two downstream redeveloping sections were 40% (USO = 0.12 ms-1), 34% (USO = 0.48 ms-1), 28% (USO = 0.12 ms-1), and 29% (USO = 0.12 ms-1) respectively.