Magnetic field dependent thermal conductivity measurements of magnetic nanofluids by 3ω method

• Published in: Journal of magnetism and magnetic materials 2019-03, Vol.474, p.199-206
• Main Authors: Doganay, Serkan, Turgut, Alpaslan, Cetin, Levent
• Format: Article
• Language: English
• Subjects: 3ω method; Air gaps; Field strength; Heat conductivity; Heat transfer; Iron oxides; Magnetic field; Magnetic fields; Magnetic nanofluid; Magnetism; Nanofluids; Nanoparticles; Non-uniformity; Nonuniformity; Permanent magnets; Temperature gradients; Thermal conductivity
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2018.10.142

•The thermal conductivity enhances with the addition of magnetic nanoparticles.•External magnetic field causes a further thermal conductivity enhancement.•The enhancement increases up to a point then it decreases.•Non-uniformity of the magnetic field has an important role on the thermal conductivity.•The direction of the magnetic field has an influence on the thermal conductivity. This study aims to investigate the thermal conductivity of the Fe3O4-water magnetic nanofluid under the influence of external magnetic field. The Fe3O4-water magnetic nanofluid sample with 4.8% vol. concentration was purchased. Then, it is diluted to four different vol. concentrations of 1, 2, 3, 4%. The external magnetic field in the range of 0–400 G was applied in parallel and perpendicular directions to the temperature gradient generated by the thermal conductivity measurement probe. Before thermal conductivity measurements, the external magnetic field generated in the air gap between permanent magnets has been analyzed both numerically and experimentally. Then a non-uniformity parameter was defined to relate magnetic field in measurement region to chain aggregation of the nanoparticles. Thermal conductivity measurements were conducted with 3ω method. The results showed that the thermal conductivity enhances with the increasing of the magnetic field strength up to a specific point, then the enhancement decreases. It is also observed that this specific point varies according to the particle concentration. Unlike the most of available study in the literature, in this study the lower thermal conductivity enhancements were obtained. The maximum enhancements with the highest concentration were 10% and 5.6% in parallel and perpendicular orientations, respectively.