Effects of drag-reducing polymers on the flow patterns, pressure gradients, and drag-reducing rates of horizontal oil–water flows

The effects of drag-reducing polymers on the flow patterns, pressure gradients, and drag-reducing rates of oil–water two-phase flows were investigated using a horizontal acrylic pipe with an inner diameter of 25.4 mm and No. 7 white oil with a viscosity of 10.6 mPa∙s and a density of 888.9 kg/m3 at 25 °C. An aqueous solution of polyacrylamide (PAM), with a molecular weight of 19 million Daltons and a concentration of 100 ppm, was used. In the experiment, the oil and water velocities were 0.1-1.5 m/s and 0.1-1.6 m/s, respectively. The DRPs were found to extend the transition boundaries of stratified flow (ST), ST with mixing at the interface (ST&MI), dispersion of oil in water and water (Do/w&w), and oil and dispersion of oil in water (o&Do/w) but did not change the transition boundaries of dispersion of water in oil (Dw/o). The maximum drag reduction rate could be obtained by adding the DRPs to the dispersion of oil in water (Do/w). The drag reduction effect was closely related to the oil and water velocities. An empirical model for the friction factor was established.