The Magneto-Dielectric Anisotropy Effect in the Oil-Based Ferrofluid

Hardoň, Štefan; Kúdelčík, Jozef; Jahoda, Emil; Kúdelčíková, Mária

doi:10.1007/s10765-019-2486-4

Cited by 13 publications

(6 citation statements)

References 23 publications

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“…The FTIR spectra were used for determining the refractive index ( n ), extinction coefficient ( k ), and dielectric function based on the following equations. First, the pattern was converted from transmittance T (ω) to reflectance R (ω) − The reflectance pattern R (ω) is the input spectra used for determining n (ω) and k (ω) as follows , where the phase change φ(ω) is the reflection of the photon after traveling inside the sample The φ(ω) is made more simple for computation by applying the KK relation , where j is the series of the wavenumber; if j is an odd number, then the i values are 2, 4, 6, 8, ..., j – 1, j + 1 and if the wavenumber j is even, the i values are 1, 3, 5, 7, ..., j – 1, j + 1, ...; Δω = ω i +1 – ω i . The n (ω) and k (ω) values from the analysis of FTIR spectra are shown in Figure c.…”

Section: Resultsmentioning

confidence: 99%

“…At the surface layer, the breaking of the interatomic bonding happens, and the new structure formed is indicated by the dielectric function peaks in the range from 430 to 450 cm –1. Δ(LO-TO) is the distance between two optical phonon modes, which decreases on increasing the concentration of carbon in the composites as presented in Table , probably due to the nonuniformity of the lattice in the composite semiconductor Fe 2 O 3 –carbon, and consequently the less stable structure. , …”

Section: Resultsmentioning

confidence: 99%

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Enhanced Visible-Light Absorption of Fe₂O₃ Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

et al. 2021

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Visible-light absorption is a critical factor for photocatalyst activity and absorption of electromagnetic (EM) interference application. The band gap of Fe 2 O 3 is 2 eV, which can be increased by doping with a high-band-gap material such as carbon from activated carbon (AC) with a band gap of 4.5 eV for increased visible-light absorption. The porosity decreases from 88 to 81.6%, and the band gap increases from 2.14 to 2.64 eV by increasing the AC from 10 to 25%, respectively. The photocatalytic activity takes 120 min to produce a harmless product for 10− 20% AC, but 25% AC shows 89.5% degradation in only 90 min and the potential to attenuate the EM wave up to 99% due to the RL being below −20 dB. The secondand third-cycle degradation achieved by the composite Fe 2 O 3 −AC having 25% AC is 88.2 and 86.5% in 90 min, respectively. The pore of the surface state of AC contains a trapped charge, and interaction occurs between the charge (electron/hole) and O 2 or H 2 O to produce OH and superoxide (O 2 − ) radicals. These radicals move inside the molecule of the pollutant (methylene blue (MB)) to break up the bond, with the final products being H 2 O and CO 2 . The X-ray photoelectron (XPS) spectra show that oxygen plays a key role in the interatomic bonding with Fe, C, and MB atoms. The best absorption of EM interference is −21.43 dB, with degradation reaching 89.51% in only 90 min for 25% AC due to its higher band gap and anisotropy constant. Fe 2 O 3 −carbon is a multifunctional material for the green environment because of its electromagnetic interference absorption and photodegradation of wastewater.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Enhanced Visible-Light Absorption of Fe₂O₃ Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

et al. 2021

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“…Another interesting direction of the research might be an implementation of the ferrofluids and their properties which are mentioned for instance in [10] and [11]. It could also be promising to build a complex model that would provide a digital twin of the device or to use a transient thermal model in order to evaluate whole process of oil heating.…”

Section: Discussionmentioning

confidence: 99%

Investigation of Natural Ester Insulating Fluid Properties and Thermal Model of a Transformer in Wide Temperature Range

Leffler¹,

Sobotka

Mokra³

et al. 2022

2022 International Conference on Diagnostics in Electrical Engineering (Diagnostika)

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Currently, a significant number of transformers are designed and used in the electricity distribution network. Since these machines are commonly based on an oil-paper electrical insulation system, it is crucial to know how certain important parameters of an oil behave within a wide range of ambient temperatures. Therefore, the range of temperatures should also include low temperature region as these conditions might occur in real application. The aim of this paper is to focus on the temperature dependent viscosity, density, thermal conductivity and specific heat of an oil in order to develop a strongly coupled thermal model of a transformer which is filled with biodegradable natural ester insulation fluid. Obtained results can be well applied within the design, operation and diagnostics phase of these types of electrical machines.

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“…Application of an external electric field on a nanofluid and the resulting electrohydrodynamics is one of the active methods enhancing the heat transfer, as reported recently for Alumina-oil nanofluid [18]. From this perspective, magnetic nanofluids (ferrofluids) with enhanced insulating properties [19] and controllable dielectric properties [20], are of special interest, as their structure (nanoparticle assembly) is susceptible to an external magnetic field [21]. Then, in addition to the thermal conductivity increase due to the Brownian motion and collisions of magnetic nanoparticles possibly leading to the chain-like particle networking [22], the magnetic field-induced particle assembly in ferrofluids also enhances the total heat transfer significantly.…”

Section: Introductionmentioning

confidence: 99%

Effect of ferrofluid magnetization on transformer temperature rise

Rajňák¹,

Franko²,

Paulovičová³

et al. 2022

J. Phys. D: Appl. Phys.

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In electrical engineering, the heat transfer can be enhanced by changing the thermophysical properties of insulating oils. In this paper, a single-phase power transformer with a nominal power of 5 kVA is subjected to a temperature rise test with three different transformer liquids. The first test is carried out with a novel gas-to-liquid transformer oil applied as a cooling and insulating medium. The other tests are conducted with ferrofluids based on this oil and MnZn ferrite nanoparticles of a low and a high nanoparticle concentration. The ferrofluids are characterized by magnetization curves, magnetic susceptibility and temperature-dependent magnetization measurements. The nanoparticle size distribution is determined from dynamic light scattering and the magnetization data. From the temperature rise profiles of the transformer at various inner locations, it has been found that the low-concentrated ferrofluid significantly reduces the transformer temperature rise. The enhanced cooling performance is ascribed to the thermomagnetic and natural convection, and increased thermal conductivity. The application of the ferrofluid with the high nanoparticle concentration resulted in a remarkable increase of the transformer temperature rise. The deteriorative cooling effect is attributed to the hindered natural and thermomagnetic convection due to the high ferrofluid magnetization and strong magnetic interaction of the ferrofluid with the magnetic field near the transformer core.

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The Magneto-Dielectric Anisotropy Effect in the Oil-Based Ferrofluid

Cited by 13 publications

References 23 publications

Enhanced Visible-Light Absorption of Fe₂O₃ Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

Enhanced Visible-Light Absorption of Fe₂O₃ Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

Investigation of Natural Ester Insulating Fluid Properties and Thermal Model of a Transformer in Wide Temperature Range

Effect of ferrofluid magnetization on transformer temperature rise

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The Magneto-Dielectric Anisotropy Effect in the Oil-Based Ferrofluid

Cited by 13 publications

References 23 publications

Enhanced Visible-Light Absorption of Fe2O3 Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

Enhanced Visible-Light Absorption of Fe2O3 Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

Investigation of Natural Ester Insulating Fluid Properties and Thermal Model of a Transformer in Wide Temperature Range

Effect of ferrofluid magnetization on transformer temperature rise

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Product

Resources

About

Enhanced Visible-Light Absorption of Fe₂O₃ Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties

Enhanced Visible-Light Absorption of Fe₂O₃ Covered by Activated Carbon for Multifunctional Purposes: Tuning the Structural, Electronic, Optical, and Magnetic Properties