Experimental evaluation of thermal conductivity, viscosity and breakdown voltage AC of nanofluids of carbon nanotubes and diamond in transformer oil

The present work reports new experimental results concerning the thermal conductivity, viscosity and breakdown voltage of solutions of diamond nanoparticles and multiwalled carbon nanotubes dispersed in mineral insulating oil for electrical transformers. The thermal conductivity of the solutions (also named nanofluids) was measured using the transient hot wire method. A controlled stress rheometer operating with coaxial cylinders was used for obtaining the shear stress versus shear rate curves and dynamic viscosity measurements. The dielectric strengths of the nanofluids were evaluated through the measurements of the insulation breakdown voltage AC using a dielectric strength analyzer with brass electrodes. From the experimental results, it was found that thermal conductivity and dynamic viscosity increase with increasing the particle concentration. On the other hand, and similarly to what is observed in the literature, the addition of these nanoparticles to the oil decreases its breakdown voltage. (C) 2015 Elsevier B.V. All rights reserved.