In an airlift bioreactor, what is the name of the vessel region where spent (off) gas disengages from the circulating liquid before leaving the system?
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Adowncomer
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Bdisengagement zone
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Cair riser
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Dflotsam
Answer
Correct Answer: disengagement zone
Explanation
Introduction:Airlift bioreactors circulate liquid by density differences created through gas injection, enabling gentle mixing with low shear. Understanding each hydraulic region is essential for oxygen transfer, gas hold-up, foam control, and cell viability. A key feature is the area where the injected gas separates from the liquid phase before exiting as off-gas.
Given Data / Assumptions:
- The vessel has two main circulation zones: an aerated riser and a non-aerated downcomer.
- Gas is injected at the base of the riser and must separate from liquid at the top.
- The question asks for the region name where gas disengages prior to venting.
Concept / Approach:The top section of an airlift is deliberately expanded to lower superficial velocities and promote phase separation. This expanded headspace is called the disengagement zone. It reduces bubble carry-under into the downcomer, manages foam, and conditions off-gas leaving the reactor. Correct naming of regions is foundational for scale-up discussions and mass-transfer calculations (for example, kla estimation).
Step-by-Step Solution:
1) Identify gas entry at the riser bottom; bubbles ascend with liquid due to reduced density.2) At the reactor top, geometry widens; velocity decreases.3) Lower velocity enhances bubble–liquid separation.4) This widened, separation-focused area is termed the disengagement zone.5) Off-gas exits through vents after disengagement; liquid returns via the downcomer.Verification / Alternative check:Design drawings typically label the upper enlarged section as the disengagement zone; computational fluid dynamics and tracer studies show reduced gas hold-up in the downcomer, confirming effective separation at the top.
Why Other Options Are Wrong:
- Downcomer: The liquid flows downward here; it is not where gas is released.
- Air riser: This is the aerated upflow section, not the separation region.
- Flotsam: Refers to floating debris, not a bioreactor region.
Common Pitfalls:Confusing the location of gas separation (top, expanded section) with regions defined by flow direction (riser vs downcomer). Another mistake is assuming foam breakers replace the need for a proper disengagement zone; geometry still matters for stable operation.
Final Answer:disengagement zone