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This contribution is devoted to study of dielectric and magnetodielectric properties in transformer oil based magnetic uid. The dielectric permittivity and their anisotropy at various mutual orientation electric (50 Hz) and magnetic eld were shown at the dierent volume concentrations of nanoparticles at room temperature. The linear increase of dielectric constant with volume concentration was conrmed which is in good agreement with the theoretical Maxwell prediction. The dielectric anisotropy factor g(B, ω) is very close to g = 1. The values of permittivity increased with the increase of volume fraction of magnetite nanoparticles. The highest value of anisotropy characterized by deviation of permittivity ∆ε = ε ∥ − ε ⊥ was found for the highest volume concentration which could mean that no aggregation of magnetite nanoparticles had appeared.

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A material property that is of crucial importance for many industrial applications is the effective thermal conductivity. This property is a function of the thermal conductivities of components, their geometry, the spatial distribution of the components (including volume fraction and shape), the thermal resistances between phases, the possible contact between the filler particles and their size distribution law. The way the particles size distribution law influences the effective properties is not yet established, due to the fact that this law is not characterized in a unitary way. The numerous equivalent diameters (depending on the measurement technique) and the lack of a methodology of correspondence between them, complicates the solving of the problem regarding the size distribution dependence of the composite materials effective properties. The main goal of this paper was to introduce the predictions regarding the influence of the descriptors of the particle size distributions on the thermal conductivity of a composite material. It was found that the mean diameter is an inconsistent parameter for comparing the effective thermal conductivities of composite materials, and that the coefficient of variation offers an alternative criterion, as well as the Pearson's mode skewness.

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