Brag reduction of non-newtonian fluids in a circular pipe with a highly water-repellent wall

With a highly water-repellent wall pipe in the drag reduction of polymer so lutions, a flow system in which drag reduction is obtained in both laminar and turbulent flow ranges was realized Experiments were carried out to meas ure the pressure drop in pipes with a highly water-repellent wall and an ac rylic resin wall by a pressure transducer. The basic material of the highly water-repellent coating is fluorine-alkane-modified acrylic resin with add ed hydrophobic silica, which was left overnight in air after it was coated to the pipe wall The diameter of the pipe was 6 mm. The polymer solutions t ested were PEO15 aqueous solutions in the concentration range of 30 similar to1,000 ppm. The drug-reduction ratio for laminar flow was about 11 simila r to 15%. To understand this effect, the pressure drop was measured by usin g surfactant solutions and degassed water, and by pressurizing tap water in the pipeline. The laminar drag was not reduced in surfactant solutions, al though degassed water and pressurizing tap water in the pipeline had no eff ect on the reduction. In the laminar flow range, the friction factor of a p ower-law fluid with fluid slip was analyzed by applying the modified bounda ry condition on fluid slip at the pipe wall, and the analytical results agr eed with the experimental results by the low Reynolds number range.