In this paper, a passive micromixer with interdigital structure is proposed and investigated using numerical simulations. The micromixer contains three layers to achieve the interdigital flow structure. The height of mixing channels is fixed as 0.2 mm. The total width of inlets is 0.9 mm. The mixing regime is rectangular in shape. The Reynolds number, measured at the entrance of straight channel, ranges from 5 to 60. Grid independence is performed to minimize the influence of numerical diffusion on simulation results. The grid size is selected as 6 μm, which can be considered as optimal. The interdigital micromixers with straight downstream channels are designed and simulated. In order to achieve better mixing near the inner walls, uneven lamellae width of each species is applied to create a larger concentration gradient near the inner walls. The results show that the micromixer with uneven lamellar width is able to enhance the mixing near the inner walls. A new passive micromixer with the uneven interdigital inlets is also designed to improve the mixing efficiency at high Re. The simulation results show that this new micromixer has a mixing efficiency larger than 80%, and a maximum pressure drop of 2.7 KPa.

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