Numerical study of the effects of internal and external forces on the nanoparticle mixing in a ferrofluid flow

Micromixers are an essential part of microfluidic devices. Numerous studies have previously discussed improving the mixing efficiency in micromixers. In the present study, the scale analysis of different forces has been done to predict their influence on the behavior of the particles. Results show that the order of the magnitude of gravitational force is lower than other forces in this study and it is not effective. Then, in the absence of the magnetic field, the effects of different forces on the mixing of magnetic nanoparticles have been studied using the one-way coupling method. According to the numerical results, it is observed that the Brownian force is essential for the normal behavior of nanoparticles. The thermophoretic force causes the penetration of particles into pure water, but homogeneous mixing does not occur. Finally, two methods have been introduced to improve mixing, including increasing the velocity of ferrofluid and magnetic field implementation. Both approaches make particle distribution more homogeneous. Incidentally, both of the above-mentioned factors are useful for improving the mixing process. Using them together yields more homogeneous mixing in a shorter length of the mixing channel.