Effects of surface modification and surfactants on stability and thermophysical properties of TiO2/water nanofluids

TiO2/water nanofluids are prepared by adding different surfactants and utilizing surface modification technique. The dispersion stability of TiO2 in water is evaluated, and better stability is found in Tetramethylammonium hydroxide (TMAH) added nanofluids and 3-aminpropyltriethoxysilane (APTS) treated nanofluids. Then the effects of nanoparticle concentration and temperature on thermophysical properties of the above two nanofluids are investigated. The viscosity of nanofluids increases with the increase of nanoparticle concentration, and decreases with temperature. The viscosity of APTS treated TiO2/water nanofluids is obvious higher than that of TMAH added TiO2/water nanofluids, because the grafting of APTS enhances the adhesion of nanoparticles to water. The thermal conductivity and effective thermal conductivity of nanofluids increases with the increase of temperature and nanoparticle concentration. And the changing trends and enhancement ratios of thermal conductivity for two nanofluids are similar. Finally, by applying properties enhancement ratio (PER), the thermal performance of TiO2/water nanofluids is evaluated. (C) 2021 Elsevier B.V. All rights reserved.