Simulação numérica do escoamento de dispersões à base de óleo de transformador elétrico em cavidades fechadas

Abstract

This work had the purpose to analyze the heat transfer, promoted by buoyancy forces, of colloidal dispersions of nanoparticles in transformer oil inside closed cavities. To achieve this purpose, measurements of some properties of the dispersions of diamond and carbon nanotubes in transformer oil, produced by a two-step method, were made: thermal conductivity, by the transient hot wire method; dynamic viscosity, by rheometers of concentric cylinders with shear stress controlled; and dielectric strength, with a dielectric strength analyzer of manual adjust. The results of these measurements were used in numerical simulations of the ows of the dispersions and of the transformer oil inside closed cavities. The numerical results were obtained via two numerical codes, based on Finite Volume Method (FVM), one for 2D ows, that had its development as part of this work, and the other for 3D ows, previously developed. The results showed that, in terms of heat transfer, the nanoparticles dispersions have increased about 23% the convection heat transfer coe_cient of the pure oil for a same Grashof number. However, the use of these nanoparticles led a reduce of 95% in the dielectric strength of the pure oil. Therefore, these results are very important in terms of the applicability of nanoparticles dispersions in electrical transformers.