| Summary: | To enhance fluid mixing, a new approach for inlet flow modification by adding vortex-inducing obstacles (VIOs) in the inlet channels of a T-shaped micromixer is proposed and investigated in this work. We use a commercial computational fluid dynamics code to calculate the pressure and the velocity vectors and, to reduce the numerical diffusion in high-Peclet-number flows, we employ the particle-tracking simulation with an approximation diffusion model to calculate the concentration distribution in the micromixers. The effects of geometric parameters, including the distance between the obstacles and the angle of attack of the obstacles, on the mixing performance of micromixers are studied. From the results, we can observe the following trends: (i) the stretched contact surface between different fluids caused by antisymmetric VIOs happens for the cases with the Reynolds number (<i>Re</i>) greater than or equal to 27 and the enhancement of mixing increases with the increase of Reynolds number gradually, and (ii) the onset of the engulfment flow happens at <inline-formula><math display="inline"><semantics><mrow><mi>R</mi><mi>e</mi><mo>≈</mo><mn>125</mn></mrow></semantics></math></inline-formula> in the T-shaped mixer with symmetric VIOs or at <inline-formula><math display="inline"><semantics><mrow><mi>R</mi><mi>e</mi><mo>≈</mo><mn>140</mn></mrow></semantics></math></inline-formula> in the standard planar T-shaped mixer and results in a sudden increase of the degree of mixing. The results indicate that the early initiation of transversal convection by either symmetric or antisymmetric VIOs can enhance fluid mixing at a relatively lower <i>Re</i>.
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