Intermig impellers in aerobic bioprocessing: what features and flow direction characterize this impeller type and why are they useful for gas dispersion?

Introduction / Context:
Intermig impellers are variants tailored for gas–liquid contacting in bioreactors. They combine axial pumping with features that enhance bubble dispersion and reduce coalescence, improving oxygen transfer at lower power inputs compared with some radial impellers.

Given Data / Assumptions:

• Gas-sparged, baffled tank with typical submergence.
• Intermig blades include protrusions/extensions to interact with gas holdup.
• Aerobic organisms require effective O2 transfer and moderate shear.

Concept / Approach:
Axial pumping sweeps bubbles upward, promoting circulation and residence time. The fork-like or profiled extensions on Intermig blades promote bubble cutting and redistribution, leading to higher interfacial area without excessive shear. The upward-directed flow pattern complements aeration strategies that enter from below.

Step-by-Step Solution:

Verification / Alternative check:
Vendor data and CFD/visual studies show Intermig patterns with enhanced gas dispersion and lower power per kLa than some radial turbines.

Why Other Options Are Wrong:

• “None” and “purely radial” contradict established descriptions.

Common Pitfalls:
Assuming only Rushton turbines disperse gas effectively; modern axial designs often outperform at scale with lower energy.

Final Answer:
All of the above.