Modeling of Laminar Flow Static Mixers

uids has a wide range of industrial applications, especially in the pharmaceutical, biomedical, consumer product, and petrochemical industries. Yet, they are also quite diffi cult to model using traditional CFD methods. Veryst Engineering collaborated with Nordson EFD to fi nd the best way to model these devices, and improve and optimize them. Static mixers are inexpensive, accurate and can handle a wide range of fl uids and mixing proportions. In many cases, the fl uids to be blended are very viscous, and as molecular diffusion in laminar fl uid mixing is very small, the fl uids have to be mechanically mixed. This is in sharp contrast to turbulent mixing, or mixing of gases that involve signifi cantly higher diffusion. The laminar fl uid mixers analyzed in this study involve multiple elements that divide and recombine the fl ow, elements that invert the fl ow to move fl uid away from the external boundary layer, and helical elements that stretch and fold the fl ow. A good mixing quality is obtained when the outlet of the static mixer has no concentrated volumes of either mixed materials and is overall uniform. Figure 1 shows disposable static mixers from Nordson EFD used to mix adhesives for construction, industrial and automotive bonding and repair applications. Accurate CFD modeling is valuable for understanding and optimizing static mixers. However, two-phase CFD modeling by itself cannot be used due to numerical diffusion, a computational artifact that does not refl ect the actual mixing process. This diffusion can be reduced with fi ner mesh, less stabilization, and other numerical techniques. However, numerical diffusion always dominates over the very low molecular diffusion present in static laminar fl uid mixing.