(456b) Scale up/Scale Down of Impulse Mixer Using CFD

imPULSE mixers provide unique flow and mixing characteristics that make them attractive for certain mixing applications especially at medium to larger scales. They also inherently are less susceptible to vortexing and air entrainment from the top. Instead of relying on the typically rotating impeller to provide the agitation, they rely on an oscillating mixer that can provide the required power by unit volume (P/V), as shown in Figure 1.

From a modeling standpoint, they do pose unique challenges though. The continuously changing geometry because of the mixer oscillation requires the implementation of a moving and deforming (MDM) technique that must be both efficient (i.e., allow for fast simulation) and maintain good accuracy for the eventual species mixing part of the simulation (i.e. avoid numerical diffusion). An additional complexity that is inherent to imPULSE mixers is the presence of “flaps” within the mixers that “open” during the upward stroke and “close” during the downward stroke. This on-off behavior of the flaps augments the effect of the mixer motion on the flow field within the vessel and enhances the mixing process.

In this current work, we will present a novel way to represent the presence of the flaps using a porous media approach. The porous media representing the presence of the flaps will have a time varying flow resistance that drops to zero during the upward stroke and has an artificially high value during the downward stroke. In addition, the “mesh layering” technique will be used to re-mesh the domain as the mixer oscillates. It is also noted that this method is the most efficient and accurate among re-meshing techniques and is ideal for oscillatory motion in general.

Finally, three different scales will be simulated and compared using the proposed approach, namely the current size of 5,000-L, 3,000-L, and a 250-L size with respect to their P/V and blend time.