Stability and rheological properties of nanofluids containing ZnO nanoparticles, poly(propylene glycol) and poly(vinyl pyrrolidone)

• The ZnO nanoparticles have been dispersed in PPG, PPG–H2O, PVP–H2O and PPG–PVP.
• Stability of these nanofluids was verified by UV–vis spectroscopy and zeta potential.
• Particle size analyzer has also been made for investigated nanofluids.
• Rheological properties were measured for nanofluid of ZnO in PPG, PVP and PPG–PVP.
• Eyring-NRTL and Eyring-mNRF models have been used for fitting the viscosity values.

In this work, polymer based nanofluids have been prepared by dispersing the ZnO nanoparticles in base fluid of poly(propylene glycol), PPG, aqueous solution of PPG, aqueous solution of poly(vinyl pyrrolidone), PVP, and mixture of these two polymers. Stability and particle size distribution of these nanofluids have been studied by result analysis of UV–vis spectroscopy, zeta potential and dynamic light scattering. Viscosity values of ZnO–PPG and ZnO–PPG–H2O nanofluids have been measured at 293.15, 298.15, 308.15 and 318.15 K. The Eyring-NRTL and Eyring-mNRF models have successfully been used for correlating the viscosity values of the nanofluids investigated with temperature dependency considered. The performance of Einstein, Brinkman, Lundgren and Batchelor models in the prediction of viscosity values of ZnO–PPG nanofluid has also been tested. Rheological behavior of investigated nanofluids has been investigated over volumetric solid concentrations (φ1 = 0, 0.5, 4.5%) and shear rates (γ = 0.01–1000 s−1) at 298.15 K. The nanoparticle suspensions generally exhibited a pseudoplastic flow behavior, indicating an existence of particle aggregations in the liquid medium. Bingham plastic and Herschel–Bulkley models were used to evaluate the shear stress–shear rate dependency. The colloid yield stress was determined from these models.