Although having been increasingly studied

there is still controversy as to when the addition of nanoparticles could improve the drag reduction performance of polymer drag reducer and particularly what is the underlying mechanism from the fluid dynamics viewpoint. The drag reduction effects of adding SiO

2

nanoparticles to various polymer polyacrylamide (PAM) solutions were examined in this work. The optimal combination of SiO

2

nanoparticles with cationic polyacrylamide was confirmed. Interestingly

the addition of SiO

2

nanoparticles to cationic polyacrylamide solution was shown to be quite efficient for reducing drag

but only at higher flow rates with Reynolds numbers more than 6000

below which the nanoparticle addition is even negative. The addition of SiO

2

nanoparticles to the PAM solution is supposed to play a dual role. The first is an increase in flow resistance caused by the Brownian motion of nanoparticles

while the second is a decrease in flow resistance caused by acting as nodes to protect the polymer chain from shear-induced breaking under high shear action. At optimal nanoparticle concentration and under higher Reynolds numbers

the later effect is dominant

whi

ch could improve the drag reduction performance of polymer drag reducers. Our work should serve as a guide for the application of natural gas fracturing

where the flow rate is frequently very high.