Effect of drag reducing polymer on horizontal liquid–liquid flows

• Effect of polymer on turbulent velocities in water flows.
• Change in flow patterns and reduction in pressure drop when polymer is added in oil–water flows.
• Effect of polymer addition on interfacial wave characteristics and velocity in stratified oil–water flows.
• Changes in oil–water velocity ratio when polymer is added in the water phase.

The effect of adding a drag reducing polymer in the water phase during horizontal oil–water flows was studied experimentally. Experiments were carried out in a 14 mm ID acrylic pipe using tap water and kerosene oil (Exxsol D140: density 828 kg/m3; viscosity 5.5 mPa s at 23 °C) as test fluids. An initial master solution of the polymer (Magnafloc 1011, a copolymer of polyacrylamide and sodium acrylate) at 1000 ppm concentration was added at different flowrates into the water phase to give polymer concentrations in the test section between 2.5 and 50 ppm. Flow patterns were investigated with high speed imaging while conductivity probes were used to obtain interface properties in separated flows. It was found that as little as 20 ppm polymer in the water phase could give maximum drag reduction of about 45% during two-phase flow. When polymer was added, the region of stratified oil–water flow extended to higher superficial oil and water velocities. In separated flows, the polymer addition resulted in a decrease in the interface height and increase in average water velocity. In addition, interfacial wave amplitudes decreased while wave lengths and celerities increased. Velocity measurements in single phase water flows with particle image velocimetry showed that the addition of polymer changed the axial velocity profile and decreased the Reynolds stresses to almost zero values.