The viscosity of base fluid will increase dues to the nanoparticles
suspend into water. Hence, the frictional resistance coefficients of nanofluids flowing in the tube are necessary calculated. In this
experiment, the viscosity of nanofluids (Cu:25 nm, 0.1 wt%) was
measured by viscometer (Brookfield-DV2T). The Reynolds number
of fluid in the tube is 4000 < Re < 105, which belongs to the turbulent.
The frictional resistance coefficient can be calculated by Eq.
(6) [29].