Influence of magnetic fields on the thermal conductivity, electrical conductivity, and viscosity of iron-encapsulated multi-walled carbon nanotubes

This study explores the thermal, electrical, and dynamic viscosity properties of water-based Fe@MWCNT nanofluids, both with and without the influence of an external magnetic field, offering novel insights into the behavior of magnetic nanofluids. The research demonstrates that Fe@MWCNT nanofluids exhibit unique magnetic-responsive characteristics, with thermal conductivity showing a remarkable dependence on external magnetic fields, temperature, and volume concentration. A key finding is the 25 % enhancement in thermal conductivity achieved at a volume concentration of 0.4 % and a temperature of 323.15 K under a 0.05 T magnetic field, a significant advancement in the field of nanofluid-based thermal management. In terms of electrical conductivity, the nanofluids display a tunable range between 530 and 1600 μS/cm as the volume concentration varies from 0.1 % to 1 %. This conductivity is further modulated by temperature and magnetic fields, with increases of 5 %–30 % under 0.05 T and 30 %–70 % under 0.1 T, showcasing the potential for precise control in applications requiring adaptive electrical properties. The dynamic viscosity of the nanofluids, ranging from 0.6 to 1.2 mPa s, is intricately linked to volume concentration, temperature, and magnetic field strength. Notably, the application of a magnetic field can increase viscosity by up to 50 %, a finding that underscores the unique magneto-rheological behavior of Fe@MWCNT nanofluids. This work advances the state of the art by providing a comprehensive understanding of the interplay between magnetic fields, temperature, and nanofluid composition, offering new opportunities for the design of advanced thermal management systems and magnetically tunable fluid technologies. The results highlight the originality of the research, particularly in demonstrating the significant enhancements in thermal and electrical properties under magnetic fields, which have not been extensively explored in previous studies.