Mixing Enhancement by Microrotor in Step Channel

In this paper, the mixing enhancement of a micromixer consisting of a step channel and a shuttlecock rotor suspended in the step is numerically analyzed. Asymptotic mixing performance is investigated as a function of Strouhal and Peclet numbers by particle tracking simulation and the Eulerian approach. The simulation results show that the rotor creates downward and inward flows in behind the rotor paddles, whereas the upward and outward flows are produced in front of the rotor paddles. At a small Strouhal number, convective mixing is very poor. However, the mixing direction is rotated by 90 deg, which can reduce the mixing time by the square of the aspect ratio of the cross section of the channel. In contrast, at a relatively large Strouhal number, good convective mixing occurs. Quantitative analysis of mixing performance of the mixer demonstrates that the mixing structures are similar for the same Strouhal number and mixing is improved with increasing Strouhal number. The mixing efficiency of the mixer decreases linearly with increasing log of the Peclet number at a relatively large Strouhal number.