Separated oil-water flows with drag reducing polymers

Abstract

The effects on velocity and turbulent properties of drag reducing polymers added in the water phase of oil-water flows were studied with Particle Image Velocimetry (PIV). The experiments were performed in separated horizontal oil-water flows in an acrylic pipe with an internal diameter of 14 mm. The test fluids were tap water (1.0 mPas, density = 1000 kg/m3) and a middle distillate oil (Exxsol D140; viscosity = 5.5 mPas, density = 828 kg/m3). Magnafloc 1011 (hydrolysed copolymer of polyacrylamide and sodium acrylate, HPAM; mol. wt. = 10 × 106 g/mol) was used as drag reducing agent in the water phase at 20 ppm concentration. Results showed that the polymer reduced frictional pressure drop at all conditions studied. The addition of polymer decreased the interface height and increased the in-situ average water velocity. The velocity profile in the water phase became more parabolic compared to the flow without polymer while the maximum velocity value increased. In addition, when polymer was added the axial stress tensor decreased close to the interface and the wall but increased in the middle of the flow, while the Reynolds and radial stress tensors reduced throughout the water phase. Two types of polyethylene oxide (PEO) polymers with different molecular weights, 5 × 106 g/mol and 8 × 106 g/mol were also tested. Drag reduction was found to increase with polymer molecular weight but depended also on the mechanical degradation of the polymers at high Reynolds numbers and on their ionic strength.