A study on the flow characteristics of oil-based ferrofluid with magnetic nanoparticles in the patterned microchannel under magnetophoresis

The behaviors of magnetic nanoparticles (MNPs) and their flow characteristics in patterned microchannels filled with an oil-based magnetic nanofluid (EFH-1, Ferrotec.) were numerically investigated. The patterned microchannel contained obstacles with rectangular and triangular configurations, which were mounted on the top and bottom walls. In order to generate a magnetophoretic effect using external magnetic fields, a permanent magnet with a uniform magnetic flux density of 0.2 T (Tesla) was located in the lower part of the patterned microchannel. Coupling calculations between the magnetophoretic flow fields and the magnetic nanoparticle behaviors in the analysis model were performed using commercial code, COMSOL Multiphysics. Results showed that the magnetophoretic flow fields were affected by the applied external magnetic field directions and the vortex flow fields in the analysis model were generated around high magnetic flux density. It was also confirmed that the magnetophoretic force distributions in the analysis model under the operating conditions played a significant role in the development of the particle behaviors. In order to confirm the behaviors of MNPs in the ferrofluid, we visualized the magnetic nanoparticles in the diluted ferrofluid with 0.065% v/v using an optical microscopic set-up with a microchannel and numerically calculated the magnetophoretic force, which is the driving mechanism that moves magnetic nanoparticles in the working fluid like oil-based ferrofluid. It was found that when a magnetic field is applied, the magnetic nanoparticles in the fluid experience a magnetic force directed toward the place of maximum magnetic field strength.