Numerical Investigation of Flow and Mixing in a Microstirrer

Abstract

Low Reynolds number (Re ∼ 0.001) flow and mixing in a Y-shaped micromixer with a four-paddle rotor placed in its junction were investigated using computational fluid dynamics (CFD). The rotation speed of the rotor ω ranges from 100 to 2000 RPM (revolutions per minute). The flow visualization shows the enhance mixing by the rotating paddle that are stretching the fluid particles, up and down flows in the junction, transverse velocity in a section of the mixing channel. Further, at a high value of ω, a circulatory flow formed in the mixing channel greatly enhances the mixing rate. The mixing potential of the mixer is measured by the strain rate. The dispersive mixing efficiency coefficient is considered as a criterion for evaluating the mixer. The other criterion is the distributive mixing efficiency, which is based on the homogeneity of the concentration distribution. Both the criteria indicate that the mixing significantly improves with increasing rotation speed. With regard to obtaining similar mixing efficiency, a mixer with a rotor reduces the required length of the mixing channel as compared with that of a mixer without a rotor. The reduced length is proportional to ω.