Controlled assembly and alignment of CNTs in ferrofluid: Application in tunable heat transfer

• Published in: Journal of magnetism and magnetic materials 2019-06, Vol.479, p.170-178
• Main Authors: Yavari, Mahdieh, Mansourpour, Zahra, Shariaty-Niassar, Mojtaba
• Format: Article
• Language: English
• Subjects: Agglomeration; Alignment; Anisotropic heat transfer; Carbon nanotube; Chain-like structure; Ferrofluids; Heat conductivity; Heat transfer; Iron oxides; Magnetic fields; Magnetic nanofluid; Magnetic properties; Multi wall carbon nanotubes; Nanofluids; Nanoparticles; Temperature gradients; Thermal conductivity; Thermodynamic properties
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2019.01.078

[Display omitted] •CNTs facilitate formation of chains in MNF and result in higher TC in compare with Fe3O4 ferrofluid.•CNTs aligned through their axis in thinner chains and at border of thicker ones.•TC of the MNF under MF increases and the thermal behavior is anisotropic.•TC is higher when the heat current and MF are parallel. Nanofluids are new generation of heat transfer fluids with enhanced thermal properties. When using nanofluids, one of the major problems is aggregation of nanoparticles. In this study, in order to benefit from controlled aggregation of nanoparticles by application of magnetic field, we used magnetic nanoparticles (MNPs) as one of the most useful nanoparticles in recent energy and biomedical researches. To achieve a more precise insight about behavior of MNPs under magnetic field, a water-based nanofluid of Fe3O4/MWNTs was studied. Due to the importance of thermal conductivity (TC) of nanofluids, it was investigated for the mentioned nanofluid. Taking advantage of magnetic properties of magnetite nanoparticles besides high thermal conductivity of multi-wall carbon nanotubes, a water-based nanofluid of 0.1 wt% Fe3O4/MWNT was prepared and its thermal conductivity was measured for the situations in which temperature gradient and magnetic field were either parallel or perpendicular. The findings suggested that TC was increased by 52% and 11.9% at H = 0.14 T for the two situations, respectively. This finding proved the anisotropic behavior of magnetic nanofluid. Formation of chain-like structures of MNPs was demonstrated through a novel approach. This phenomenon was found to be the reason of thermal conductivity enhancement. Our findings show that employing Fe3O4/MWNT is a promising approach for improving heat transfer efficiency of heat carriers.