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• The combination of Ω- and straight-shaped obstacles enhance the mixing performance. • Well mixing is achieved as the obstacles are in contact with the walls of Tesla chambers. • Increasing the radius of Ω-shaped obstacles can improve the performance of micromixer. • The hexagonal chambers are better than triangle and Tesla chambers. An efficient fluid mixing performance is achieved by a Tesla/hexagon-shaped passive micromixer in a wide range of Reynolds numbers with short mixing length (4.2 mm/1.15 mm from the origin). The passive micromixers are composed of Tesla/hexagonal chambers and Ω-shaped obstacles or combined with straight-shaped obstacles that induce the generation of vortex, contraction and expansion process, the changes of the flow direction, and even the split and recombination of streams. The mixing process of two fluids (water and ferrofluid) is numerically investigated using computational fluid dynamics. For the Tesla-shaped micromixer embedded with Ω-shaped obstacles, a sufficient mixing is obtained as the obstacles are in contact with the internal walls of Tesla chambers. In the hexagon-shaped micromixer, the combination of straight- and omega-shaped obstacles greatly enhance the performance of micromixer in particular at moderate flow rate (1< Re <10). Moreover, reasonable increasing the curvature radius of the omega-shaped obstacles can further improve its mixing performance. The designed passive micromixers were also fabricated, tested and compared with the numerical results through the soft-lithography processes, and the good agreement between the experimental and numerical results identifies our predictions. The good performance of the designed micromixers provides a new direction in designing micromixer with high-throughput and short mixing length. [Display omitted] [ABSTRACT FROM AUTHOR]

• A hybrid magnetic field produced by microwires and Halbach magnets is proposed to enhance the mixing between ferrofluid and water. • We numerically and experimentally analyze the effects of the arrangement and the number of microwires on the mixing efficiency. • By adjusting the direction and the magnetite of uniform magnetic field, we receive optimal mixing efficiency 99.06%. With the development in biomedical and biotechnological areas, novel and efficient microfluidic devices integrated with sufficient and rapid mixing function have been attracting enormous scientific attention as versatile and robust platform for low cost and non-contact biological analysis and diagnose. Here, we design and fabricate a magnetic micromixer integrated with special designed microwires, a Y-shaped microchannel and uniform magnetic field for realizing rapid mixing between ferrofluid and deionized water. A comprehensive analysis on the dynamic behavior of ferrofluid is performed by using 3D Eulerian-Eulerian model. Good consistency between experiment and numerical results demonstrates that the enhanced mixing in the presence of longitudinally arranged microwires is due to the introduction of eddies, whose impacts are strengthened with the increase of the number of microwires (n w). However, increasing n w requires a long microchannel and long time to complete mixing. In order to further improve the mixing performance of our micromixer, a horizontally arranged microwire combined with a particular uniform magnetic field is proposed to provide enough magnetic force for enhancing the mixing of ferrofluid and deionized water, receiving optimal mixing efficiency 99.06%. The flexible tunability of external uniform magnetic field enables desired performance of our designed system. [ABSTRACT FROM AUTHOR]