Mixing Enhancement in a Chaotic Micromixer with Reversed Ridges and Grooves

A novel micromixer named reversed ridges and grooves micromixer (RRGM) with chaotic and passive characteristics is devised and analyzed numerically. Compared with a slanted grooves micromixer (SGM), a barrier-embedded micromixer (BEM), and a circulation-disturbance micromixer (CDM), the RRGM achieves an excellent mixing performance for Reynolds number (Re) in a range of 0.01 <= Re <= 100, especially at Re <= 10. The mixing index is adopted as the objective function to evaluate the mixing performance. The Lagrangian particle tracking method is employed to further observe the chaotic behavior in the mixing process and to explain the mechanism of chaotic mixing. The combination of ridges and grooves actively accelerates the stretching and folding of fluids, forming a pair of continuously changing asymmetrical hyperbolic vortices along the entire mixing channel. Three design parameters related to the performance, namely, slanted angle of ridges, slanted angle of grooves, and height of groove and ridge, are explored to optimize the mixing performance. The slanted angle of 45 degrees is ascertained as the optimal value for both the ridges and grooves. At Re <= 1, the height of ridges and grooves of 30 mu m is the best choice, whereas at Re >= 10, a higher mixing index is obtained by increasing the height of grooves and ridges, which is attributed to a greater flow disturbance from the inertial dominance.