In this paper, the rapid mixing of deionized water and Fe3O4ferrofluid in a Y-shaped microchannelusing a permanent magnet is studied both numerically and experimentally. The microchannel has arectangular cross section with 500 m 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 becalculated. Knowing the magnetic force, the momentum and transport-diffusion equations are solved. Asetup is designed and fabricated to carry out the experiments. The mixing process is photographed by aCCD camera for 5 min until the mixing process reached a steady state condition. The numerical resultsare compared with the corresponding measurements to validate the simulations. The effect of differentparameters 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 investigatedon the mixing efficiency. Applying magnetic field considerably improves the mixing efficiency of themicromixer and reduces the mixing length. Increasing the mass fraction of nanoparticles and magneticfield strength increases the mixing efficiency until the magnetization of the ferrofluid reaches its saturatedlevel. Increasing the fluid flow, however, lowers the mixing efficiency and increases the mixing length.

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