Rapid mixing in micromixers using magnetic field

- Increasing the magnetic field strength reduces the mixing length.
- By increasing the volume flow rate, the mixing efficiency decreases.
- The mixing length is linearly related to the flow rate with a slope of 0.3.
- Increasing the nanoparticle mass fraction improves the mixing efficiency.

In this paper, the rapid mixing of deionized water and Fe3O4 ferrofluid in a Y-shaped microchannel using a permanent magnet is studied both numerically and experimentally. The microchannel has a rectangular cross section with 500 μm in width and 1 mm in depth. The process, assumed to be two-dimensional and steady state, is simulated by COMSOL numerical software. In the numerical simulation, the Maxwell equations are solved to obtain the magnetic potential. Then, the magnetic force can be calculated. Knowing the magnetic force, the momentum and transport-diffusion equations are solved. A setup is designed and fabricated to carry out the experiments. The mixing process is photographed by a CCD camera for 5 min until the mixing process reached a steady state condition. The numerical results are compared with the corresponding measurements to validate the simulations. The effect of different parameters such as magnetic field's strength (1280G, 2000G and 3000G), volume flow rate (30 cc/min, 40 cc/min, and 60 cc/min), and mass fraction of nanoparticles (0.0125, 0.025 and 0.05) is investigated on the mixing efficiency. Applying magnetic field considerably improves the mixing efficiency of the micromixer and reduces the mixing length. Increasing the mass fraction of nanoparticles and magnetic field strength increases the mixing efficiency until the magnetization of the ferrofluid reaches its saturated level. Increasing the fluid flow, however, lowers the mixing efficiency and increases the mixing length.