43 / 2018-08-16 19:44:54

The Challenges and Opportunities of Nanofluids

Nanofluids, transformer oil, insulating particles, semiconducting particles, dielectric properties, thermal properties,industrial application

The development of several nanofluids is reviewed regarding the materials of liquids, additives, manufacturing methods, and various (electrical, thermal, chemical, and physical) properties. Advantages and disadvantages are studied and analyzed with the addition of several types of insulating nanoparticles and semiconducting nanoparticles into transformer oils. Special attention is paid to the dielectric property, thermal performance, environmental impact of different concepts, as well as their potential applications to power devices. To qualify different concepts, measurement tools are introduced and used in getting the parameters of nanofluids. These experimental techniques include, such as, scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Karl-Fischer titration, breakdown tests at impulse voltage, AC voltage and DC voltage, Weibull analysis program, surface flashover measurement, dielectric spectroscopy to measure permittivity, resistivity and dissipation factor, space charge measurement, specific heat capacity measurement, thermal conductivity measurement, as well as oxidation stability test.
A couple of formulations were further selected in making investigation into their breakdown and over-voltage breakdown properties. Experimental results show that the semiconducting nanoparticles of magnetite (Fe3O4) and zinc oxide (ZnO), are able to reduce the streamer propagation velocity in a divergent electric field at both positive and negative polarities. However, the impact of insulating nanoparticles, such as aluminium oxide (Al2O3) and silicon dioxide (SiO2), on the streamer propagation velocity is limited. Selected nanoparticles are able to increase the breakdown strength and reduce the breakdown data scattering of an insulation system, and thus the low probability values of breakdown of the insulation system are able to be increased. Experimental results show that the mean breakdown voltage of a nanofluid can be increased by 30 % over the original fluid at a positive impulse voltage. The AC partial discharge inception voltage is able to be increased. Cooling performance can be improved. Nanoparticles have even a healing effect in increasing the dielectric and thermal performances of used oils.
However, experimental results do show that nanofluids in some cases have inferior oxidation stability than original fluids. Furthermore, moisture uptake, agglomeration, sedimentation, as well as long-term reliability of nanofluids are the challenges to the potential application of them to power industry, such as to power equipment, such as transformers.
The issue of moisture uptake is able to be improved with the introduction of several types of nanoparticles, such as cerium oxide (CeO2) and hexagonal boron nitride (h-BN). With the introduction of suitable surfactant the oxidation stability of nanofluids is able to be improved. It was reported that the thermal conductivity of a transformer oil based h-BN added nanofluid was able to be enhanced by up to 100 % in comparison with the original transformer oil. Continuous study on this topic is going on.
It might be concluded that several colloidal liquid systems with suspended insulating and semiconducting nanoparticles have been developed during the last 25 years. Nanofluids have a potential for being used in power equipment with enhanced dielectric and thermal properties. However, the addressed challenges remain, which need to be well managed for the realistic application of nanofluids to power industry.