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Nanofluid synthesis in pure water is associated with premature settlement resulting in least dispersion stability. Therefore, in this study, polyacrylamide (PAM) is used as viscosity enhancer to improve dispersion stability of nanofluid stabilized by composites of silica and titania. Different techniques such as dynamic light scattering measurements, electrical conductivity, scanning electron microscopy, and rheological studies are used to support the analysis. The use of silica and titania nanoparticles together with PAM has additional advantage over particle agglomeration, and thus, the dispersion stability improved. Further, nanofluid stabilized by composites of silica and titania was tested for rheological measurements at 90°C to find nanotechnology applicability in high-temperature applications. The shear-thinning behaviour of nanofluids at high temperature (90°C) was least affected by shear deformation and reduced to 0.48 mPa.s at higher shear rate (4200 s−1), while shear thinning of PAM solution seriously varied with increasing shear deformation and takes the edge of 0.0005 mPa.s at higher shear rate (4200 s−1). In addition, the thermal stability of nanofluids was better due to slight decrease in viscosity with increasing temperature, which makes them suitable to be utilized at high-temperature applications in widespread industrial areas including oilfield where the temperature becomes a major factor. [ABSTRACT FROM AUTHOR]

For solar thermal harvesting, an experimental study was performed on the thermal absorption performance of water-based carbon nanotubes (CNTs), Cu, and Al2O3 nanofluids using a halogen lamp-based thermal radiation system. The effect of nanoparticle concentrations (0.01 wt.%, 0.1 wt.%, and 1 wt.%) on the nanofluid dispersion, stability, and thermal absorption characteristics was investigated, and a comparative analysis was performed for each type of nanofluid. All types of nanofluids increased the absorbance and electrical conductivity with increasing nanoparticle concentration, which contributed to improving the thermal absorption performance of nanofluids. The results showed that the thermal absorption performance was high in the order of carbon-based nanofluids (CNTs), metal-based nanofluids (Cu), and oxide-based nanofluids (Al2O3). In CNTs nanofluids, the thermal absorption performance expressed the time reduction rate, which was 12.8%, 16.3%, and 16.4% at 0.01 wt.%, 0.1 wt.%, and 1 wt.% test cases, respectively. Therefore, the 0.1 wt.%-CNTs nanofluid is more economical and appropriate. However, in Al2O3 nanofluids, the time reduction rate of the 1 wt.% nanofluid was significantly higher than that of the 0.01 wt.% and 0.1 wt.% nanofluids. In Cu nanofluids, unlike CNTs and Al2O3 nanofluids, the time reduction rate constantly increased as the nanoparticle concentration increased. [ABSTRACT FROM AUTHOR]

Nanotechnology provides a new way to improve the insulating properties of traditional dielectric materials. In this study, three types of mineral oil based nanofluids were prepared by suspending Fe3O4, TiO2 and Al2O3 nanoparticles all of which were surface modified by oleic acid. The inception voltage, stopping length and propagating velocity of streamers in the nanofluids under positive lightning impulse voltage were experimentally studied. It is found that nanoparticles can restrain the initiation and propagation processes of positive streamers in transformer oil depending on the types of nanoparticles. In addition, the trap characteristics in pure oil and nanofluids were comparably studied. The relationship between the trap characteristics and mobility of charge carriers in oil samples were then established. The increased trap density in nanofluids diffuses kinetic energy of ionized electrons and converts them into negative ions, resulting in the reduced electrical field strength in front of positive streamer and increased breakdown strength of nanofluids. [ABSTRACT FROM AUTHOR]