Investigating the Effect of Magnetic Field on the Thermal Conductivity of Ferrofluid Containing Fe3O4 and CoFe2O4 Spinel Ferrite Nanoparticles and Presenting a New Correlation

In this study, the effect of the presence of a magnetic field (MF) on the thermal conductivity of the nanofluid (NF) ( ) containing spinel ferrite nanoparticles (NPs) (MFe2O4, M=Fe, Co) was investigated. CoFe2O4 NPs were concentrated by the coprecipitation method. Both NPs were characterized by SEM, EDX, XRD, and VSM. The thermal conductivity was investigated and compared in the presence and absence of an MF. In addition to the intensity of MF (100, 200, 300, and 400 G), the effect of the concentration of NPs (from 0.25 to 2 Vol%) on at a constant temperature of 25 °C was investigated. According to the results, in the absence of MF, the of CoFe2O4/water ferrofluid (FF) was higher than that of Fe3O4/water FF in different concentrations. Furthermore, as the intensity of the MF increased, the of both Fe3O4/water and CoFe2O4/water FFs increased. This increase was more observed for the FFs containing Fe3O4 NPs. At the highest concentration (2 Vol%), with the increase of MF up to 400 G, the of Fe3O4/water has increased by about 3.2%, while this increase was about 1.8% for CoFe2O4/water. Increasing the volume percentage of NPs also had a positive effect on the thermal conductivity coefficient. Finally, according to the obtained results, correlations were presented to predict the of both FFs according to the intensity of the MF and the concentration of NPs. The proposed correlations had a satisfactory accuracy with R2 values of 0.98 for both FFs.