Experimental investigation on thermal conductivity of MFe₂O₄ (M = Fe and Co) magnetic nanofluids under influence of magnetic field

Highlights: • A comparative study is conducted to examine thermal conductivity of different MNFs. • Fe₃O₄ nanoparticles show higher saturation magnetization than that of CoFe₂O₄. • New empirical correlations are proposed to predict thermal conductivity of MNFs. - Abstract: In present study, the thermal conductivity of magnetic nanofluids (MNFs) containing MFe₂O₄ (M = Fe and Co) nanoparticles suspended in deionized water are investigated in the absence and the presence of uniform magnetic field. Fe₃O₄ and CoFe₂O₄ nanoparticles are synthesized using the co-precipitation method. The X-ray diffraction, transmission electronic microscopy and vibration sample magnetometer are used to characterize the structure, size and magnetic properties of nanoparticles. The thermal conductivity of MNFs are measured at different volume fractions between 0% and 4.8% and the magnetic field intensity range of 0–500 G. The experimental results show that the thermal conductivity of MNFs increases with increase in volume fraction and magnetic field intensity before reaching its saturation point. Finally, new correlations are presented based on the experimental results to predict thermal conductivity of MNFs in both the absence and the presence of magnetic field