Fermentor hydrodynamics: What internal hardware is primarily used to suppress vortex formation and improve gas–liquid dispersion (aeration efficiency) in a stirred tank?
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AImpeller
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BBaffles
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CSparger
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DDraft tube
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EFoam breaker
Answer
Correct Answer: Baffles
Explanation
Introduction / Context:Good mixing and gas dispersion are vital for oxygen transfer. Vortex formation wastes power and reduces mass transfer; proper internals prevent this and enhance performance.
Given Data / Assumptions:
- Standard baffled stirred tank reactor.
- Goal is to reduce swirling vortex and improve aeration.
- Gas is introduced via a sparger; agitation by an impeller.
Concept / Approach:Baffles are vertical strips mounted on the vessel wall. They break tangential flow, reduce vortexing, and promote top-to-bottom circulation, which in turn improves bubble dispersion and oxygen transfer.
Step-by-Step Solution:
Identify vortex cause: excessive tangential flow.Apply solution: wall baffles disrupt swirl and enhance axial mixing.Select “Baffles” as the primary hardware for this function.Verification / Alternative check:Design handbooks recommend 4 baffles at about 1/10 vessel diameter for optimal performance.
Why Other Options Are Wrong:
Impeller: provides power input but does not by itself suppress vortexing.Sparger: introduces gas; not used to prevent vortex.Draft tube / Foam breaker: different purposes.Common Pitfalls:Assuming higher impeller speed alone will improve dispersion; without baffles, it worsens vortexing.
Final Answer:Baffles.