Determination of Dynamic Viscosity and Stability for Single and Hybrid Nanofluids of SiO2, TiO2, MWCNT and ZnO Nanoparticles

In this study, the stability and viscosity of four different nanoparticles are discussed in conjunction with the physical properties of these nanoparticles. The aim is to provide guidance for nanoparticle selection in future nanofluid applications. Additionally, our goal is to examine hybrid nanofluids in comparison to single nanofluids, exploring their potential benefits and evaluating their industrial applications. A two-stage approach was employed, using ethylene glycol (EG) as a base fluid, to create these nanofluids. Single nanofluids were formed with SiO₂, TiO₂, MWCNT, and ZnO nanoparticles at 0.1%, 0.5%, and 1% volume concentrations. Additionally, binary (SiO₂–TiO₂/EG), ternary (SiO₂–TiO₂–MWCNT/EG), and quaternary (SiO₂–TiO₂–MWCNT–ZnO/EG) hybrid nanofluids were formed with 0.1% volume concentrations. The dynamic viscosity of all nanofluids was evaluated over the temperature range of 20–50 °C. Analysis of nanofluids was extended by characterization studies using field emission transmission electron microscopy (FE-SEM), field emission scanning electron microscopy (FE-TEM), Zeta potential testing, and visual inspection. SiO₂ nanoparticles exhibited the greatest stability, remaining in suspension for more than 28 days without sedimentation, while ZnO nanoparticles were the least stable, collapsing in < 7 days. Compared to ethylene glycol, ZnO/EG had the most increased viscosity (42.79%) at 20 °C and a 1% volume concentration. However, SiO₂–TiO₂–MWCNT/EG showed the largest decrease in viscosity (9.99%) at 20 °C. Hybrid nanofluids exhibit better viscosity performance compared to their base fluids and single nanofluids, enhancing the thermal efficiency of these heat transfer fluids. Additionally, this study is groundbreaking research as it emphasizes the efficiency of hybrid nanofluids as well as introducing quaternary nanofluids to the literature.