With a highly water-repellent wall pipe in the drag reduction of polymer solutions, a flow system in which drag reduction is obtained in both laminar and turbulent flow ranges was realized. Experiments were carried out to measure the pressure drop in pipes with a highly water-repellent wall and a nacrylic resin wall by a pressure transducer. The basic material of the highly water-repellent coating is fluorine-alkane-modified acrylic resin with added 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 tested were PEO15 aqueous solutions in the concentration range of 30 approx 1,000 ppm. The drag-reduction ratio for laminar flow was about 11 approx 15%. To understand this effect, the pressure drop was measured by using surfactant solutions and degassed water, and by pressurizing tap water in the pipline. The laminar drag was not reduced in surfactant solutions, although degassed water and pressurizing tap water in the pipeline had no effect on the reduction. In the laminar flow range, the friction factor of a power-law fluid with fluid slip was analyzed by applying the modified boundary condition on fluid slip at the pipe wall, and the analytical results agreed with the experimental results in the low Reynolds number range.
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