On Drag Reduction from Apparent Wall Slip in Highly Viscous Newtonian Fluid Pipe Flow

In the pipeline transport of highly viscous fluid, replacing viscous fluid with Newtonian fluid with lower viscosity around the pipe wall could reduce the shear stress in the wall boundary and lower fluid flow drag to save energy. Theoretical considerations and numerical evaluations are made in the paper with two viscosity pipe flows. Relations among thickness of low viscous layer (apparent wall slip layer), flow rate, drag reduction ratio, and apparent slip velocity are deduced. It is showed that drag reduction depends on the ratio of high and lower viscosity while low viscous layer close to a film, and flow drag could be negative or positive while the thickness of low viscous layer grows, and when the ratio of thickness of low viscous layer to pipe radius exceed a certain number, drag would be increased.