Thermo-physical properties of pure ethylene glycol and water–ethylene glycol mixture-based boron nitride nanofluids

Nanofluids are suspensions of solid nanoparticles in conventional heat transfer fluids, and they often exhibit improved heat transfer characteristics. Different nanoparticles (metals, oxides, nitrides, etc.) have been used for the synthesis of nanofluids. The nanosized hexagonal form of boron nitride (BN) has versatile properties, such as chemical inertness, electrically insulating and high in-plane thermal conductivity (~ 600 W m⁻¹ K⁻¹) making it a prospective dispersoid in nanofluids for heat transfer applications. The present study reports the synthesis of pure ethylene glycol (EG)- and ethylene glycol–water mixture (EG/W, 40/60 vol. ratio)-based nanofluids containing a dispersion of BN nanoparticles. Form the study, it emerged that with the increase in particle concentration, the BN nanofluids showed an increment in the thermal conductivity manifesting a maximum of 15.5% and 12.5% for 3 vol.% of BN dispersion in EG- and EG/W-based nanofluids, respectively. Also, the thermal conductivity enhancement of BN nanofluids was found to be nearly independent of temperature in the temperature range of 30–60 °C. The viscosity of BN nanofluids increased with the increase in particle concentration showing a maximum of 41 and 33% for 2 vol.% of BN in EG-based and EG/W-based nanofluids, respectively. Further, BN nanofluids exhibited shear-thinning behaviour at lower shear rates and a Newtonian nature at higher shear rates. A new correlation has been developed to estimate the thermal conductivity and viscosity of BN nanofluids on the basis of experimental data.