Effects of ultasonication and surfactant on the thermal and electrical conductivity of water – Solar glycol mixture based Al₂O₃ nanofluids for solar-thermal applications

The present experimental work aims to prepare nanofluid using Al₂O₃ nanomaterials as dispersant into a solar glycol (SG) – water mixture (80:20) and investigate its stability, density, thermal conductivity, electrical conductivity, and viscosity at three differing volume percentages, namely 0.15, 0.3, and 0.45. Oleic acid (OA) was used as a surfactant to increase the stability of the nanofluid. The concentrations of Al₂O₃ and OA used were, 0.15, 0.3, 0.45 vol%, and 2 ml, 3 ml, 5 ml, and 10 ml, respectively, while the ultasonication time was varied between 30 and 70 min. The stability of the prepared nanofluid was confirmed using the UV–Vis spectrometer, zeta potential, and by visual inspection. The Al₂O₃–SG/water-mixture-based nanofluids thermal conductivity was augmented by 26.36% at 0.45 vol% and 30 °C, within ± 5% deviation error. The dynamic viscosity of the Al₂O₃-based nanofluids was increased by ∼ 1.85 times compared to the SG-water mixture at 0.45 vol%. At 0.45 vol% of Al₂O₃ with 5 ml of OA, the nanofluid electrical conductivity was enhanced by 87.87% at a temperature of 50 °C, within ± 5% deviation error. The enhancement coefficient ratio increases with an increase in volume concentration and a reduction in temperature. It is concluded that the highly stable conductive nanofluid with excellent thermo-physical properties would be helpful to improve the overall performance and energy efficiency solar-thermal units.