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Influence of Electric Field on AC Magnetic Susceptibility of a Mineral Oil Based Ferrofluid

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Rajňák M., Dolník B., Tobiáš T., Paulovičová K., Kurimský J., Cimbala R., Kopčanský P., Timko M.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
567-579
EN
In a ferrofluid, the magnetic susceptibility at low magnetic fields is sensitive to the size and shape of magnetic nanoparticles and their concentration in a liquid carrier. In this paper we report on the AC magnetic susceptibility of a ferrofluid based on a mineral oil and iron oxide nanoparticles coated with oleic acid. As this type of ferrofluid is of increasing interest for electrical engineering applications, we investigate the effect of an external electric field and an electric current flowing through the ferrofluid on the AC magnetic susceptibility at ambient conditions. It is known that the action of the electric field on the oil based ferrofluids can result in the particle assembling. Then, the induced structural changes may affect the magnetic susceptibility of the bulk ferrofluid. In our experimental study we observed that the ferrofluid magnetic susceptibility decreases with increasing electric field. However, a heating effect with increasing electric field was observed too. Hence, it is concluded that besides the structural changes, the Joule heating has an obvious impact on the magnetic susceptibility of the ferrofluid in the external electric field.
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Rheological and Thermal Transport Characteristics of a Transformer Oil Based Ferrofluid

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Paulovičová K., Tóthová J., Rajňák M., Wu Z., Sundén B., Wadsö L., Tobiáš T., Kopčanský P., Timko M., Lisý V.
Acta Physica Polonica A
|
2018
|
vol. 133
|
issue 3
564-566
EN
Ferrofluids based on insulating liquids are intensively studied as a potential substitute of liquid dielectric in high voltage technologies. In this work we focus on the experimental investigation of flow and thermal transport characteristics of a ferrofluid based on transformer oil (Mogul) and iron oxide nanoparticles. The magneto-rheological behavior of the ferrofluid was studied by a rotational rheometer in the shear rate range from 1 to 1000 s¯¹ and magnetic field up to 1 T. By means of a thermal constants analyzer and a transient plane source method we obtained the thermal conductivity, specific heat and thermal diffusivity values for the studied oil and the ferrofluid. It is shown that the Newtonian character of the ferrofluid changes to a non-Newtonian with application of the magnetic field. The notable magneto-viscous effect has been observed especially at low shear rates. We found that the doping of the transformer oil by 3 wt% of the nanoparticles results in a thermal conductivity enhancement by about 3.2%.
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