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Generation of Fe₃O₄ Nanoparticle Aggregates in a Ferrofluid Driven by External Electric Field

100%
Kurimský J., Rajňák M., Cimbala R., Paulovičová K., Timko M., Kopčanský P., Kolcun M., Kosterec M., Kruželák L.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
907-909
EN
In the paper the experimental study of magnetic nanoparticle aggregation in a transformer oil based ferrofluid driven by an external electric field is reported. The studied ferrofluid was composed of the magnetite nanoparticles, oleic acid surfactant, and transformer oil. Generally, it is considered that superparamagnetic nanoparticles do not interact in the absence of external magnetic field. In the paper we present an experimental observation of the particle assembly formation in a direct current external electric field by optical microscopy. During the observation no external magnetic field was applied. A diluted low-polarity ferrofluid drop on a glass surface was exposed to the external static inhomogeneous electric field. It is assumed that induced dipole-dipole interaction and subsequent dielectrophoretic motion give rise to the electrohydrodynamic flow in the fluid after a certain time period. As a result, a visible particle chain was formed at the drop electrical equator. This demonstration is expected to contribute to the understanding of the streamer formation and electrical breakdown in transformer oil based ferrofluids.
2
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Analysis of Thermal Field in Mineral Transformer Oil Based Magnetic Fluids

100%
Kosterec M., Kurimský J., Cimbala R., Čonka Z., Kruželák L., Rajňák M., Timko M., Kopčanský P., Vargová B.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
937-939
EN
Growing interest in the use of magnetic fluids in power systems especially in transformers as insulation and a coolant is nowadays registered. Magnetisable nanofluids, which are used in cooling systems as an alternative to mineral transformer oil, are characterized by lower concentration of magnetic nanoparticles. The magnetic fluid has better heat transfer and dielectric properties such as breakdown than mineral transformer oil and it can be used to improve heat flow, thereby increasing the ability of the active parts to resist failures such as electromagnetic pulses. External magnetic field may be used for forced circulation of magnetic fluid. Magnetic force inside the magnetic fluid can be adequately controlled by adjusting the incident magnetic field. This paper presents thermal distribution, fluid flow and cooling ability of mineral transformer oil and magnetic fluid based on mineral transformer oil. The concentration of Fe₃O₄ magnetic nanoparticles is 0.15% volume of mineral transformer oil. The thermal field is generated by a steel conductor. Thermal distributions in mineral transformer oil and magnetic fluid are investigated and differences for both cases are discussed in the paper.
3
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Variation of Magnetic Fluid Deformation Related to Nanoparticle Concentration in Steady Electric Field

81%
Kosterec M., Kurimský J., Cimbala R., Špes M., Farkaš R., Dolník B., Gamcová M., Rajňák M., Timko M., Kopčanský P., Paulovičová K., Vargová B.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
570-573
EN
Today, it is important to know the behaviour of magnetic fluids applied in the power electrical machines, e.g. in power transformers, when exposed to an electric field. Besides their promising applications in high voltage engineering, they are of increasing interest from designed assembly and pattern formation point of view. The structure of such magnetic fluids is easily controllable by external magnetic fields. However, less attention has been paid to structural phenomena in magnetic fluids induced by electric fields. The core of this paper is dedicated to the experimental observation of a magnetic fluid droplet deformation in a steady electric field. The mutual relation between the deformation parameter and magnetic nanoparticles concentration is analysed. Spatio-temporal analysis of the droplet shape is presented in the paper. The phenomena of the droplet deformation were recorded by a camera. The detailed experimental procedure is presented. The method of deformation parameter calculation based on the linear pixel as the smallest-size unit in digital image is written. Finally, the relation between the deformation parameter and the nanoparticle volume concentration, as well as the time and magnitude of the DC field application are thoroughly evaluated. The results show that the deformation parameter decreases with increasing concentration at constant applied steady electric field but increases with increasing applied steady electric field.
4
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The Shielding Effectiveness of a Magnetic Fluid in Radio Frequency Range

81%
Dolník B., Rajňák M., Cimbala R., Kolcunová I., Kurimský J., Džmura J., Petráš J., Zbojovský J., Kosterec M., Kopčanský P., Timko M.
Acta Physica Polonica A
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2018
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vol. 133
|
issue 3
585-587
EN
This article builds on the previous work and describes the interaction of transformer oil-based magnetic fluid (MF) with the radio frequency (RF) magnetic near-field. Three prepared samples of the MF used as a barrier to magnetic near-field, consist of transformer oil and dispersed magnetite nanoparticles coated with oleic acid. We pay attention to the important area related to the electromagnetic field shielding by the MF. Such sample of the MF may be a good candidate for applications where it is necessary to simultaneously electrically isolate, remove the excess of heat and to shield electromagnetic interference (EMI). We present a method for the determination of shielding effectiveness (SE) of the MF under RF excitation conditions ranging from 500 MHz to 3 GHz. We report the effect of magnetic volume fraction in the MF and the effect of the sample thickness on the SE.
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