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Katiyar A.,Indian Institute of Technology Madras | Katiyar A.,Indian Institute of Technology Ropar | Dhar P.,Indian Institute of Technology Madras | Dhar P.,Indian Institute of Technology Ropar | And 3 more authors.
Experimental Thermal and Fluid Science | Year: 2016

Magnetic nanofluids have enormous potential to improve thermal conductivity under the influence of magnetic fields. Magnetic field induced thermal transport capabilities of metallic magnetic nanoparticles viz. Fe, Ni and Co based stable magnetic colloids under the influence of magnetic field has been reported for the first time (detailed survey of literature supports the claim). Experimental investigations reveal highly enhanced thermal conductivity of such colloids under the influence of external magnetic field. The highest magnitude of thermal conductivity enhancement ∼106% and 284% is achieved for the Fe/HTO magnetic-nanofluids w.r.to the base nanofluid and pristine base fluid (in the absence of magnetic field) respectively at 0.05 T magnetic fields and 7.0 vol.% particle concentration. Ni and Co based nanofluids demonstrate less enhancement in the thermal conductivity magnitude compared to Fe based nanofluids due to lower values of saturation magnetic moments. However, the reduction in performance is not as drastic as expected since Ni and Co possesses better thermal conductivities than Fe, leading to compensation of the reduced field response. The underlying mechanism of enhanced conduction has been explained based on the formation of stable nanoparticle chains along the magnetic field lines which act as ‘short circuits’ for the thermal waves to travel faster. The enhancement in the thermal conductivity drops gradually beyond a critical magnetic field due to zippering/self-aggregation of the chained structure. The magnetic fluids have also been observed to be reversible with low thermal hysteresis and prove to be potential candidates as smart fluids in micro-scale devices. © 2016 Elsevier Inc. Source


Katiyar A.,Indian Institute of Technology Madras | Dhar P.,Indian Institute of Technology Madras | Dhar P.,Indian Institute of Technology Ropar | Nandi T.,Defence Materials and Stores Research and Development Establishment DRDO | And 2 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2016

Magnetic field induced augmented thermal conductivity of magneto-nanocolloids involving nanoparticles, viz. Fe2O3, Fe3O4, NiO and Co3O4 dispersed in different base fluids have been reported. Experiments reveal the augmented thermal transport under external applied magnetic field. A maximum thermal conductivity enhancement ∼114% is attained at 7.0 vol% concentration and 0.1 T magnetic flux density for Fe3O4/EG magneto-nanocolloid. However, a maximum ∼82% thermal conductivity enhancement is observed for Fe3O4/kerosene magneto-nanocolloid for the same concentration but relatively at low magnetic flux density (∼0.06 T). Thereby, a strong effect of fluid as well as particle physical properties on the chain formation propensity, leading to enhanced conduction, in such systems is observed. Co3O4 nanoparticles show insignificant effect on the thermal conductivity enhancement of MNCs due to their minimal magnetic moment. A semi-empirical approach has been proposed to understand the mechanism and physics behind the thermal conductivity enhancement under external applied magnetic field, in tune with near field magnetostatic interactions as well as Neel relaxivity of the magnetic nanoparticles. Furthermore, the model is able to predict the phenomenon of enhanced thermal conductivity as a function of physical parameters and shows good agreement with the experimental observations. © 2016 Elsevier B.V. Source

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