An experimental investigation, sensitivity analysis and RSM analysis of MWCNT(10)-ZnO(90)/10W40 nanofluid viscosity

In this paper, for the first time, viscosity of MWCNT (%10)-ZnO (%90)/10W40 hybrid nanofluid is examined in different volume fractions (0.05%–1%), temperatures (5–55 °C), and shear rates (666.5–11,997 s−1). A comprehensive empirical correlation with high precision is also suggested here in order to estimate viscosity of this nanolubricant, as a function of temperature, volume fraction, and shear rate. Study of the amount of conformity of linear and exponential functions over the plots of shear stress versus shear rate in different temperatures and volume fractions, reveals a better conformity of experimental data with the exponential functions, and it is then concluded that the studied fluid is non-Newtonian fluid, and of pseudo plastic type. Investigation of variations of viscosity versus shear rate in constant volume fractions and different temperatures denotes an increase of viscosity with increasing of volume fraction. Moreover, it is shown that viscosity, with a relatively good approximation, can be considered independent of shear rate in high temperatures. With the sensitivity analysis of viscosity to a 10% variation of volume fraction, in three different shear rates, it is observed that for all temperatures and volume fractions, with a growth of shear rate, the amount of sensitivity is escalated.