  Magnetic field induced drastically augmented thermal conductivity of magneto
nanocolloids involving magnetic oxide nanoparticles, viz. Fe2O3, Fe3O4, Nickel
oxide (NiO), Cobalt oxide (Co3O4), dispersed in different base fluids (heat
transfer oil, kerosene, and ethylene glycol) have been reported. Experiments
reveal the augmented thermal transport under the external applied magnetic
field, with kerosene based MNCs showing at relatively low magnetic field
intensities as compared to the heat transfer oil and EG based MNCs. A maximum
thermal conductivity enhancement of 114 % is attained at 7.0 vol. %
concentration and 0.1 T field intensity for Fe3O4/EG magneto nanocolloid.
However, a maximum of 82% thermal conductivity enhancement is observed for
Fe3O4/Kerosene magneto nanocolloid for the same concentration but relatively at
low magnetic field (600 G). 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. An analytical 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 analytical model is able to predict the
phenomenon of enhanced thermal conductivity as a function of physical
parameters such as chain length, size and types of nanoparticles, fluid
characteristics, magnetic field intensity, saturation magnetic moment,
nanoparticle concentration etc. and good agreement with the experimental
results has been observed.
