Numerical Investigation of the Mixing Efficiency in Square-Wave Passive Micromixers for Microfluidic Device Applications

This numerical study investigated the mixing efficiency and pressure drop characteristics of water-based liquid flow through five different serpentine-type microchannel structures with a square cross-section, for Reynolds numbers Re between 0.5 and 40. The cost of mixing was also evaluated here in terms of pressure drop and input power required to transport the fluid through the channel. The passive micromixer models were characterized by a constant hydraulic diameter of 200 μm, with the height H and pitch Pi of the microchannel modified at the values from 0.6 to 1 mm and 1.2 to 2 mm, respectively, maintaining a constant Pi/H ratio of 2. At Re = 2, Re = 10 and Re =30, the mixing efficiency for the model with Pi = 2 mm and H = 1 mm was 1.27, 1.1 and 1.26 times the mixing indexes of the model with Pi = 1.2 mm and H = 0.6 mm, respectively. This enhanced mixing quality was obtained with the sacrifice of a lower mixing index to pressure drop ratio (1.18, 1.32 and 1.13 times lower) and a higher mixing cost in terms of input power (1.18, 1.49 and 1.15 times higher).