High molecular weight polymer solutions or surfactant solutions are typical
examples of complex fluids. They exhibit nonlinearity in viscosity and drag reduction
occurs in the turbulent pipe flow even if the concentration is very dilute. They are
generally known as non-Newtonian fluids. By applying a hydrophobic wall pipe to
reduce drag on the flow of polymer solutions, a flow system was constructed, wherein
drag reduction was obtained in both the laminar and turbulent flow ranges. In
discussions of Newtonian fluid in Chapter 2, we dealt with apparent slip flow
analytically using Navier’s hypothesis, and the result was compared with the
experimental findings of the friction factor. The experimental results of PEO
(polyethylene oxide) aqueous solutions with a concentration range of 30-1000 ppm and
the analytical result for the friction factor of a power-law fluid with fluid slip were
analyzed by applying the modified boundary condition on fluid slip, as described in this
chapter.
Keywords: Drag reduction, laminar flow, complex fluid, turbulent drag
reduction, pipe flow, friction factor, highly water-repellent wall, slip velocity,
power-law model, polyethylene-oxide solutions, surfactant solutions, contact
angle.
