Dielectric relaxation spectroscopy of hybrid insulating nanofluids in time, distribution, and frequency domain

• Published in: Journal of molecular liquids Vol. 409; p. 125409
• Main Authors: Havran, Peter, Cimbala, Roman, Dolník, Bystrík, Rajňák, Michal, Štefko, Róbert, Király, Jozef, Kurimský, Juraj, Paulovičová, Katarína
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2024
• Subjects: Depolarization current; Dielectric Relaxation Spectroscopy; Distribution domain; Frequency domain; Hybrid nanofluids; Time domain; Frequency domain; Time domain; Dielectric Relaxation Spectroscopy; Hybrid nanofluids; Depolarization current; Distribution domain
• ISSN: 0167-7322
• DOI: 10.1016/j.molliq.2024.125409

•A significant dispersion of the charging current characteristics of nanofluids with magnetic nanoparticles is observed.•At lower electric field intensities, the increasing fullerene concentration of the hybrid nanofluids reduces the charging currents up to a charging time of 200 s.•Magnetic nanofluid shows the highest values of conductivity currents.•At higher electric field intensities in the low-frequency spectrum, the relaxation peaks decrease when the concentration of fullerene in hybrid nanofluids increases.•Compared to lower electric field intensities, at the value of 333.3 kV/m, several polarization processes are captured in the entire frequency spectrum. Improving the dielectric properties of insulating liquids belongs to the modern motivation to optimize the operation of high-voltage devices. Hybrid nanofluids can provide the mentioned improvement, and thus, it is necessary to reveal their hidden potential. This study investigates hybrid nanofluids with different concentrations of magnetite and fullerene nanoparticles, a separate fullerene and magnetic nanofluid, and a base carrier fluid based on gas-to-liquid technology. The investigated samples are subjected to dielectric relaxation spectroscopy analysis at three applied electric field intensities in the time, distribution, and frequency domain. The lack of information about the studied parameters of the mentioned nanofluids is another reason for our experimental measurements. A significant dispersion of the charging current characteristics of nanofluids with magnetic nanoparticles is observed. At lower electric field intensities, the increasing fullerene concentration of the hybrid nanofluids reduces the charging currents up to a charging time of 200 s. Magnetic nanofluid shows the highest values of conductivity currents. Experiments show that the suspension of fullerene in the base oil causes a higher charging current and a more pronounced relaxation response than pure base oil. Significant relaxation information in the low-frequency band is detected from the distribution spectra. At higher electric field intensities in the low-frequency spectrum, the relaxation peaks decrease when the concentration of fullerene in hybrid nanofluids increases. The distribution area shows the effect of higher polarizability of magnetite nanoparticles. Compared to lower electric field intensities, at the value of 333.3 kV/m, several polarization processes are captured in the entire frequency spectrum. The frequency-dependent complex permittivity confirms the findings from the time and distribution domains. Comparing the distribution domain with the frequency domain shows higher sensitivity and accuracy in capturing relaxation processes in the distribution domain.