Effect of Carbon Nanotube Additives on Drag Reduction in Pipe Flows

The drag reduction effects of dispersing carbon nanotube (CNT) additives into water-glycerin pipe flow were investigated experimentally. While nanofluid (i.e. fluids with nano-scale additives) drag reduction from the addition of long and flexible polymers into turbulent flows has been long identified, the mechanism that causes this effect is not yet fully understood. Other additives such as rigid polymers, surfactants, and bubbles have also been shown to be effective drag reducing agents. In the current work, high molecular weight polymers such as polyethylene oxide (PEO) as well as CNT additives produced significant drag reduction in both the transitional and turbulent regimes. CNTs were shown, for the first time, to enhance the drag reducing characteristics of polymer additives. CNTs were chosen in place of traditional nano-scale fibers in order to take advantage of their high strength properties in an attempt to reduce degradation and scission effects. The results were quantified by measuring the pressure drop across a downstream test section after the flow was fully developed. Reynolds numbers between about 500 and 5000 were studied in order to provide sufficient detail from laminar to transitional and turbulent flow regimes. The additive dispersion quality was also investigated over multiple dispersion techniques.