The dual behavior of the dynamic viscosity of multiwalled carbon nanotubes–Al2O3 (3:7)/ethylene glycol hybrid nanofluids: an experimental study

This study investigates the behavior of nanofluids containing multiwalled carbon nanotubes (MWCNT) and Al2O3 nanoparticles based on ethylene glycol. To that end, the MWCNT and Al2O3 nanoparticles were combined in 3:7 ratios. The nanofluids in solid volume fractions (SVFs) of 0.04–0.3%, at a temperature range of 25–50 °C and different shear rates, were prepared and investigated. The nanofluids displayed two different behaviors: non-Newtonian behavior in 0.3% SVF and Newtonian behavior in all other SVFs. Increasing the nanofluid temperature at constant SVF decreased its viscosity. Response surface methodology was used to develop a model to predict nanofluid viscosity with a regression coefficient of 0.96, which indicates the model's suitability. The viscosity sensitivity to SVFs indicated the significant impact of the concentration on nanofluid in 0.3% SVF.