High aspect ratio vessels with multiple impellers are used as gas-liquid contactors for their high gas hold-up and mass transfer rate. In aerobic bioprocesses they are especially prevalent and find use in the production of antibiotics, enzymes, and therapeutic proteins, to name a few. However, macromixing in a large-scale (cubic meters) multi-impeller tank tends to be severely limited, which leads to heterogeneities if the time-scale of reaction competes with that of mixing . Some reductions in the macromixing time have been realized in experiments by relocating the single feed point from the top to the middle . Additionally, both the number and placement of feed points have been found to influence mixing times in pneumatically agitated bubble column and airlift reactors .