Flow Mechanism of a Novel Active Micro-Rotor Mixer

Abstract

The purpose of this study is to investigate the complex vortex flow patterns within a novel active micro-rotor mixer under various Reynolds numbers and rotating speeds by employing of CFD technique. The concept of present micro-rotor mixer is inspired from the Wankel-type combustor which is widely used in the power machines. The configuration of present micro-mixer is consisted of a rotor with shape of triangle column, a blending chamber and individual inlet and outlet ports. The blending chamber is served as the mixing chamber since the separated three sub-regions will change their volumes as the rotor undergoing the rotating motion with a fixed eccentricity. The dynamic flow patterns and mixing process of two species within the mixing chamber were simulated and visualized with streak lines. The governing equations are unsteady, two-dimensional incompressible Navier-Stokes equation and the two working fluids are pure water and alcohol. The concentration equation for species is also solved to reveal the mass transfer process in various sub-regions then being calculated on the outlet port to evaluate the mixing efficiency. The dynamic mesh technique was applied to re-distribute the computational meshes when the rotor finished a complete rotation cycle. Inspection on the flow developing stages within the mixing chamber over one complete cycle, it seems that multi-vortex flow field was generated due to the interaction of the shear force from the rotor, viscous force and inertial force of working fluids. The Coanda flow appeared in some conditions. When the Reynolds number is below of 10, the rotating speed of rotor has less influence on the mixing efficiency. An obvious enhancement in the mixing efficiency can be found in cases of the rotating speed of rotor changed from 30 rpm to 150 rpm when the Reynolds number in range of 25 to 100. Generally, the maximum mixing efficiency of 85% can be achieved for 1<Re<100 which demonstrated that present design was effective for μ-TAS.