Evaluation of surfactant on stability and thermal performance of Al2O3-ethylene glycol (EG) nanofluids

This paper includes examinations of thermo-physical parameters and performance evaluation of Al2O3- EG nanofluids with temperature ranging from 20 to 60 °C for volume fraction of 1.0 vol%. Two different surfactants of Polyvinylpyrrolidone (PVP) and Sodium Dodecyl Sulfate (SDS) are added to improve the stability of Al2O3- EG nanofluids. Firstly, sedimentation observation and TEM images confirm its stability and observe inherent morphology. Secondly, the ratio of surfactant mass fraction to volume fraction of nanofluid (ωpvp/φ) is optimized by measuring viscosity and thermal conductivity. Thirdly, two different evaluated criteria based on properties enhancement ratio (PER) and figure of merit (FOM) are used to assess the overall thermal performance of nanofluids under single phase forced convective flow. The results show that, according to TEM images and quantitatively calculated by the velocity ratio (uB/ut) of the Brownian to settling velocity ratio of nanoparticles, Al2O3 - EG nanofluids with PVP surfactant provide the best stable suspensions due to polymeric chain interaction. With the increase in PVP surfactant concentration, both viscosity and thermal conductivity firstly increase up to a maximum value, after which, it decreases. There is an optimum PVP concentration (ωpvp/φ = 0.15 for 1.0 vol% Al2O3- EG nanofluids) resulting in the highest thermal conductivity and relative low viscosity. From evaluated criteria, Al2O3-EG nanofluids with ωpvp/φ ratio ranged from 0 to 0.15 and temperature below 50 °C can be considered as efficient working fluids under the laminar and turbulent forced convective process. Therefore, this nanofluid is a promising approach for energy management in the low temperature waste heat recovery system. [Display omitted] •The stability of Al2O3-EG-PVP nanofluids is qualitatively investigated by Sedimentation method and TEM images.•The degree of nanoparticles aggregation is quantitatively estimated by the Brownian to settling velocity ratio.•The effect of surfactant concentration on thermo-physical parameters is discussed.•Evaluated criteria are used to assess the thermal efficiency of Al2O3-EG nanofluids.