Numerical characterization of low Reynolds number flow in the Kenics static mixer

• Published in: Chemical engineering science 1998-04, Vol.53 (8), p.1565-1584
• Main Authors: Hobbs, D.M., Swanson, P.D., Muzzio, F.J.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; Mixing
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/S0009-2509(97)00132-2

Low Reynolds number flow in a six element Kenics static mixer was modeled using finite element computations. The numerical approach takes into account aspects of the fluid flow within the Kenics mixer which have been neglected in previous studies, including transitions between mixer elements and finite-thickness mixer plates. The pressure drop information obtained from the simulations was compared to several experimental correlations available in the literature for Kenics mixer pressure drop. Analysis of the low Reynolds number velocity field indicates a spatially periodic flow which matches the periodicity of the mixer geometry. Flow transitions at the entrance and exit of each element strongly affect the velocity field for up to ∼25% of the element’s length under creeping flow conditions. Comparison of the velocity field over a range of Reynolds numbers from 0.15 to 100 indicated that Reindependent velocity profiles are obtained up to Re=10, with significant deviations in the velocity field at Reynolds numbers above this limit. The magnitude of the rate-of-strain tensor, which represents an upper bound for mixing efficiency, was computed and profiled within the mixer. The profile for the magnitude of the rate-of-strain tensor was roughly uniform over the central 75% of a single mixer element, but shifted toward higher values in the end regions, indicating that the greatest potential mixing effects take place at the element-to-element transitions.