Magnetic Field Effect on Thermal, Dielectric, and Viscous Properties of a Transformer Oil-Based Magnetic Nanofluid

Michal Rajnak,Katarina Paulovicova,Peter Kopcansky,Jana Tothova,Juraj Kurimský,Zan Wu,Bengt Sunden,Milan Timko,Bystrik Dolnik,Roman Cimbala,Lars Wadsö

doi:10.3390/en12234532

Michal Rajnak, Katarina Paulovicova + Show 9 more

Open Access

https://doi.org/10.3390/en12234532

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Journal: Energies	Publication Date: Nov 28, 2019
Citations: 32	License type: CC BY 4.0

Affiliation: Technical University of Košice, Lund University

Abstract

Progress in electrical engineering puts a greater demand on the cooling and insulating properties of liquid media, such as transformer oils. To enhance their performance, researchers develop various nanofluids based on transformer oils. In this study, we focus on novel commercial transformer oil and a magnetic nanofluid containing iron oxide nanoparticles. Three key properties are experimentally investigated in this paper. Thermal conductivity was studied by a transient plane source method dependent on the magnetic volume fraction and external magnetic field. It is shown that the classical effective medium theory, such as the Maxwell model, fails to explain the obtained results. We highlight the importance of the magnetic field distribution and the location of the thermal conductivity sensor in the analysis of the anisotropic thermal conductivity. Dielectric permittivity of the magnetic nanofluid, dependent on electric field frequency and magnetic volume fraction, was measured by an LCR meter. The measurements were carried out in thin sample cells yielding unusual magneto-dielectric anisotropy, which was dependent on the magnetic volume fraction. Finally, the viscosity of the studied magnetic fluid was experimentally studied by means of a rheometer with a magneto-rheological device. The measurements proved the magneto-viscous effect, which intensifies with increasing magnetic volume fraction.

Highlights

Electrical equipment, like power transformers, inherently operate with energy losses, which lead to rises in temperature
We investigate the three key quantities of an magnetic nanofluids (MNFs) based on a novel, commercially available transformer oils (TO)
The viscous properties of the MNF samples under a magnetic field were studied by using an Anton In Figure 4a, we present the dependence of the thermal conductivity (TC) of the MNF on the

Summary

Introduction

Electrical equipment, like power transformers, inherently operate with energy losses, which lead to rises in temperature. Some of the studies report huge increments in thermal conductivity [13,14,15], while others refer to smaller increments, with the applied magnetic field [16,17] These differences are found for similar types of MNF samples and similar measurement setups used. The effect of an external magnetic field and the induced heterogeneous nanoparticle structure results in magneto-dielectric anisotropy [32]. This is mostly characterized by higher dielectric permittivity measured in the parallel configuration of electric and magnetic fields as compared to perpendicular configuration. We report on the unusual magneto-dielectric anisotropy and complement the study with the measurements of the viscosity of the MNF dependent on the magnetic field and magnetic volume fraction

Materials and Methods

Method

Thermal

Dependence

Dielectric Permittivity

Findings

Conclusions