Laminar flow and chaotic advection mixing performance in a static mixer with perforated helical segments

The laminar flow and chaotic mixing characteristics of a high-viscosity fluid in static mixers with staggered perforated helical segments were numerically investigated in the range of Re=0.1-150. The numerical results of pressure drop of Kenics static mixer have a good agreement with the reported data from the literature. The effects of aspect ratio A _r and Reynolds number on the mixing performance of Modified Kenics Static Mixers (MKSM) were evaluated by Darcy friction coefficient, shear rate, stretching rate, and Lyapunov exponent, respectively. The product of f×Re for MKSM linearly increased with the increase of Re, but it was constant under Re<10. The values of shear rate in the first perforated hole of mixing elements gradually became much larger by 1.10%-11.78% than those in the second perforated hole with the increasing Re. With the increase of dimensionless axial mixing length, the stretching rate increased linearly and the sensitivity for initial condition gradually weakened. A larger A _r is beneficial for micro-mixing in creeping flow. The average Lyapunov exponent linearly increases with the increase of Re. The profiles of Lyapunov exponent at different dimensionless perforated diameter (d/W) and perforated spacing (s/W) indicate that the chaotic mixing in MKSM is much more sensitive to d/W than s/W. A dimensionless parameter η taking into account the mixing degree and pressure drop was employed to evaluate the mixing efficiency. The optimization of perforated helical segments with the highest mixing efficiency at Re=100 was d/W=0.55 and s/W=1.2.