Abstract: For analyzing the mixing characteristics of the three-dimensional staggered oriented ridges (SOR) micro mixer, a Lagrangian tracking technology based on computational fluid dynamics (CFD) is used to simulate numerically the distortion of the fluid line and fluid surface on the fluid channel section in the mixer，and the mixing effect is further evaluated quantitatively by the calculation of mean lineal stretching. The results show that the SOR flow channels induce the chaotic advection, which increases the contact area of the fluid particle and improves the mixing efficiency. On small Reynolds number, the mean lineal stretching has little change when Reynolds number increases. But on large Reynolds number, the mean lineal stretching increases with the increasing of Reynolds number.

Key words: Chaotic advection, Lagrangian tracking, Microfluidic, Static micro-mixer