19Fax: +33 (0) 2 23 23 40 51 20 21Abstract: 22 23Experimental results on the steady state viscosity of carbon nanotubes water-based nanofluids 24 are presented considering the influence of particle volume fraction and temperature ranging 25 from 0 to 40°C. The suspensions consist of multi-walled carbon nanotubes dispersed in de-26 ionized water and they are stabilized by a surfactant. The aspect ratio of nanotubes is close to 27 160 and the particle volume fraction varies between 0.0055% and 0.55%. It is shown that the 28 nanofluids behave as shear-thinning materials for high particle content. For lower particle 29 content, the nanofluids are quite Newtonian. It is also observed that the relative viscosity of 30

The effects due to temperature and shearing time on viscosity for Al 2 O 3 /water and CNT/water based nanofluids at low concentration and low temperatures are experimentally investigated. The viscosity data were collected using a stress-controlled rheometer equipped with parallel plate geometry under up and down shear stress ramp. CNT and Al2O3 water based nanofluids exhibited hysteresis behaviour when the stress is gradually loaded and unloaded, depending also on shearing time. Experiments also showed that the nanofluid suspensions indicated either Newtonian or nonNewtonian behaviour, depending on shear rate. CNT water based nanofluid behaves as Newtonian fluid at high shear rate whereas Al 2 O 3 water based nanofluid is non-Newtonian within the range of low temperatures investigated.