Contribution of magnetic nanoparticle in thermal conductivity of flake-shaped iron particles based magnetorheological (MR) fluid

摘要

Magnetorheological (MR) fluids were prepared in transformer oil as well as transformer oil based magnetic fluid having 2wt. % of Fe3O4 particles. The thermal conductivity enhancement (w.r.t. carrier) in the case of transformer oil based MR fluid under a field was found to vary from 219%, 304%, and 356%, respectively, from 15 vol. %, 20 vol. %, and 25 vol. % of iron concentration. These values are much higher than that obtained for spherical-shaped iron particles based MR fluids. This is further enhanced by another 30% at the same magnetic field when the same flakes were dispersed in transformer oil based magnetic fluid. In addition, the magnetic fluid based MR fluids exhibit minimum hysteresis in thermal conductivity when the field is removed. The increase in the thermal conductivity of transformer oil based MR fluid is due to the shape effect as well as the reduction in thermal resistance due to a higher particle-particle interaction compared to spherical particles. In addition, on adding nanoparticles, the friction between the particles reduces and nanoparticles facilitate flake-shaped particles to form a stronger chain. This results in an enhancement in thermal conductivity. The observed reduction in the viscosity of MR fluids with nanoparticles supports the concept of the increased orientation of flakes in the direction of the field.