Thermal Conductivity Of Magnetic Nanofluids Research Articles

Enhanced magnetic heating efficiency and thermal conductivity of magnetic nanofluids with FeZrB amorphous nanoparticles

Magnetic heating and thermal conductivity of magnetic nanofluids (MNFs) are of great interest for biomedicine and electronic heat transfer. Here, we report the enhanced magnetic heating efficiency and thermal conductivity of MNFs fabricated by amorphous FeZrB nanoparticles with high saturation magnetization and good magnetothermal stability. Under external magnetic fields, the viscosities of FeZrB MNFs are almost twice that of Fe3O4 MNFs, enhancing the field-driving force in heat transfer applications. Under 250 Oe alternating current fields, the required time of heating FeZrB MNFs to the hyperthermic temperature (45 °C) is only 16.5% that of Fe3O4 MNFs, amplifying the specific absorption rate of the magnetic nanoparticles by about 2.4 times. Benefiting from the higher thermal conductivity of amorphous, the thermal conductivity enhancement for FeZrB MNFs is also larger than that of Fe3O4 MNFs—up to 34.0% enhancement for silicone oil-based FeZrB MNF at φ = 2 vol%. This investigation of amorphous-nanoparticle-including MNFs shall shed light on the potential of utilizing amorphous nanoparticles to fabricate MNFs for biomedicine or heat management applications.

Studying thermal conductivity of magnetic nanofluids in constant magnetic field

Studying thermal conductivity of magnetic nanofluids in constant magnetic field

Maneuvering thermal conductivity of magnetic nanofluids by tunable magnetic fields

We report an experimental investigation of magnetic field dependent thermal conductivity of a transformer oil base magnetic fluid as a function of volume fractions. In the absence of magnetic field, thermal conductivity increases linearly with an increase in volume fraction, and magnitude of thermal conductivity thus obtained is lower than that predicted by Maxwell's theory. This reveals the presence of clusters/oligomers in the system. On application of magnetic field, it exhibits a non-monotonous increase in thermal conductivity. The results are interpreted using the concept of a two-step homogenization method (which is based on differential effective medium theory). The results show a transformation of particle cluster configuration from long chain like prolate shape to the aggregated drop-like structure with increasing concentration as well as a magnetic field. The aggregated drop-like structure for concentrated system is supported by optical microscopic images. This shape change of clusters reduces thermal conductivity enhancement. Moreover, this structure formation is observed as a dynamic phenomenon, and at 226 mT field, the length of the structure extends with time, becomes maximum, and then reduces. This change results in the increase or decrease of thermal conductivity.

Deterioration in effective thermal conductivity of aqueous magnetic nanofluids

Common heat transfer fluids have low thermal conductivities, which decrease their efficiency in many applications. On the other hand, solids have much higher thermal conductivity values. Previously, it was shown that the addition of different nanoparticles to various base fluids increases the thermal conductivity of the carrier fluid remarkably. However, there are limited studies that focus on the thermal conductivity of magnetic fluids. In this study, thermal conductivity of magnetic nanofluids composed of magnetite nanoparticles synthesized via co-precipitation and thermal decomposition methods is investigated. Results showed that the addition of magnetite nanoparticles decreased the thermal conductivity of water and ethylene glycol. This decrease was found to increase with increasing particle concentration and to be independent of the synthesis method, the type of surfactant, and the interfacial thermal resistance.

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

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 0–500G. 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.

Effect of chain-like magnetite nanoparticle aggregates on thermal conductivity of magnetic nanofluid in magnetic field

This paper investigated the effect of chain-like magnetic nanoparticles aggregates on the thermal conductivity of magnetic nanofluids (MNFs) in magnetic field via a proposed model of thermal conductivity of MNFs. The anisotropic feature of thermal conductivity ratio was predicted based on the field induced chain-like magnetic nanoparticles aggregates in MNFs. It was indicated that for a magnetic field parallel to temperature gradient, the thermal conductivity component along the magnetic field was significantly enhanced due to the magnetic field induced chain-like magnetic nanoparticles aggregates. The experimental data of thermal conductivity enhancement along the magnetic field direction were similar to those predicted by the proposed model.