Experimental investigation on rheological properties of water based nanofluids with low MWCNT concentrations

The rheological properties of water based MWCNT nanofluids are investigated at five different low volume concentrations (0.0047%, 0.0238%, 0.0571%, 0.1428%, 0.2381%) and five low temperatures (275 K, 277 K, 279 K, 281 K, 283 K) by a novel experimental method in the present study. The present methodology combines the 31TT test and the DSO test. Measurements show that the nanofluids are featured with clear thixotropy and shear thinning behaviors when the concentration is above 0.0571%. It is further shown that the thixotropy becomes less obvious as the concentration lowers implying a stronger Newtonian fluid characteristic. Therefore the concentration of 0.0571% can be regarded as the critical point quantifying the transition from Newtonian to non-Newtonian and this critical concentration is independent of temperature. It is also observed that relative viscosity increases slightly with temperature at medium shear rate. Moreover, temperature sweep measurement suggests that the viscosity decreases with temperature firstly and it increases beyond a critical temperature, which can be curbed by raising the shear rate for solutions with concentration lower than 0.0571%. The dependency of the relative viscosity of the MWCNT nanofluids on shear rate, temperature and concentration is obtained and a new and accurate correlation is developed for engineering application. (C) 2019 Published by Elsevier Ltd.