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A novel spiral micromixer with sinusoidal channel walls was designed to enhance the mixing index in the low to intermediate Reynolds number range (1 < Re < 100). To analyze the fluid flow, a set of numerical simulations were performed using the finite-difference method. The microchip was fabricated from polydimethylsiloxane, employing the soft-lithography technique. The degree of mixing was increased by 99.11 % when using the proposed micromixer, compared to 59.44 % for a simple spiral micromixer. The introduced microchannel drastically reduced the mixing length, increasing the mixing index of a 0.5-loop spiral-sinusoidal microchannel compared to that of the simple spiral microchannel with 1.5 loops. The mixing index of the 3-loop mixer was higher than that of the microchannel with 1.5 loops, and its pressure drop was increased.

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In this study, forced convection heat transfer of water/FMWCNT nanofluid is studied inside a rectangular microchannel with triangular ribs on the lower wall numerically. The nanofluid flow is affected by a uniform magnetic field. The ribs have an insulating wall and a wall at a constant temperature. The other walls of the microchannel are insulated. Slip boundary condition is imposed on the walls and the temperature jump is ignored. The effect of different parameters such as Reynolds number, Hartmann number, slip coefficient and volume fraction of nanoparticles on the velocity and temperature distributions are investigated. The results are presented as the velocity and temperature profiles and local and average Nusselt numbers. The results demonstrate that the heat transfer rate and Nusselt number increase with the Reynolds number and the intensity of the magnetic field. Also, an enhancement in the volume fraction of nanoparticles and the slip coefficient leads to an increase in the heat transfer rate.

The effective mixing process is critical in biological and chemical processes. The main objective of the present study is to investigate the influence of normal and Halbach magnet arrays on the mixing performance of a three-inlet micromixer numerically. In this microdevice, ferrofluid is injected into the center inlet, and water is injected into two other inlets. The influence of Remanent Flux Density Norm (RFDN), number of magnets, magnet distance from the main microchannel entrance, and inlet flow rate is considered. It is revealed that the micromixer with magnets exhibits a 165% improvement in the mixing efficiency compared to the one with no magnetic field. The results show that increasing the magnetic field does not always increase the mixing quality. Even in some cases, it has a negative effect. It is demonstrated that the mixing efficiency is strongly influenced by the magnet arrangement. An optimal position is found for the magnet arrangement to achieve the maximum mixing efficiency of 91%. Contrary to the normal configuration, Halbach magnet array creates a parabolic profile for flux density. Halbach array can improve the mixing performance, depending on all magnets’ RFDN. The proposed microchannel can be used as a useful device for biological applications.