Comparison of various synthesis methods of magnetic nanoparticles, and of the various experimental methods used for their characterization

It has been a hot issue to enhance the thermal conductivity of a fluid with nanoparticles, i.e. nanofluids. Ferrofluid is one good candidate because it has dispersion stability. Around 8 nm Mn-Zn ferrite ferrofluid was synthesized by a coprecipitation method. Thermal conductivity enhancements of 3.5, 9.7, and 24 % were achieved at 0.9, 2.8, and 5.5 vol. %, respectively, which were measured with a transient hot-wire method at 25 oC. These values were higher than the magnetite based ferrofluid because Mn- Zn ferrite has higher bulk thermal conductivity than that of magnetite. The enhancement was independent on the temperature,

and it exceeded the Maxwell theory limit. Mn-Zn ferrite based ferrofluid can be applied to the heat transfer fluid because of its enhanced thermal conductivity with probable dispersion stability.