Experimental Investigation of Thermal Conductivity and Effusivity of Ferrite Based Nanofluids under Magnetic Field

We investigate the effect of magnetic field ( ) on the thermal conductivity ( ) and effusivity ( ) of cobalt ferrite based nanofluids having different concentrations ( ). Cobalt ferrite nanoparticles (NPs) have been synthesized using the microwave assisted method. At high volume fraction of cobalt ferrite nanoparticles in water ( > 0), both thermal parameters have been found to be suppressed relative to and of water in the absence of . However, it is seen that percentage values of the effusivity in perpendicular field direction show negative to positive variation, and thermal conductivity in parallel field direction shows negative to zero variation. 1. Introduction Enhancement in of magnetic nanofluid under the effect of applied has been reported by Philip et al. [1]. It is also reported that these properties are suppressed for doped metal oxide based nanofluids and with the application of [2, 3]. Both these behaviors in thermal transport properties are the outcome of different nature of phonon transport in metal, metal oxide, and doped metal oxide nanoparticle (NP) based nanofluids (NFs). Experimental data about enhancement alone does not reflect that other transport properties ( , specific heat) are also affected in a similar manner with respect to . It was pointed out that this ambiguity creates the problem when looking for efficient nanofluids in terms of transport properties [4]. If we can characterize nanofluids with respect to the previous three transport properties, with and without application of , then we can better select the most appropriate nanofluid for desired application. Effusivity, also named thermal admittance or contact coefficient, is defined as the material’s ability to exchange heat with surroundings. It is defined through [5, 6] where is the thermal conductivity, is the density, is the specific heat, is the thermal diffusivity, and has the dimensions of . Potential applications of NFs depend upon the enhancement in transport properties and in turn on their behavior under the applied . Hence, it is of great importance to corroborate the reported experimental results [2, 3], which is the aim of the present study. Dadarlat et al. [2] have used high accuracy photopyroelectric technique to obtain thermal properties of cobalt ferrite (CoFe2O4) based NFs, and compared with the other studied magnetic fluids, they also reported that transport properties of CoFe2O4 NFs have been degraded with increasing volume fraction . Djurek et al. [3] also reported decrease in of CoFe2O4 NFs with application of . However, none of the authors gives an