Agitation and Aeration problems
- 1. For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (kL) co-relating power consumption (Pm) and fermenter volume (V) can be expressed as
Options- A. kL ? (Pm/V)0.33
- B. kL ? (Pm/V)0.66
- C. kL ? (Pm/V)0.50
- D. kL ? (Pm/V) Discuss
Correct Answer: kL ? (Pm/V)0.33
- 2. During fermentation, the saturation concentration of oxygen was reduced from 7 ppm. to 1 ppm. Which one of the following conclusions can be drawn?
Options- A. Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration
- B. Microbial growth is not oxygen limited since the oxygen concentration is lesser than the saturation concentration
- C. Experimental error leads to the reduction
- D. No conclusion can be drawn Discuss
Correct Answer: No conclusion can be drawn
- 3. A fermentation system has a KLa of 3 s-1 and a C0* of 5 ppm of O2. If the bulk liquid is completely depleted of oxygen, then the oxygen transfer rate will be equal to
Options- A. zero
- B. 15 mg.l-1.s-1
- C. 10 mg.l-1.s-1
- D. 5 mg.l-1.s-1 Discuss
Correct Answer: 15 mg.l-1.s-1
- 4. Impeller damage can be minimized by
Options- A. using specially designed axial flow impellers
- B. using radial flow impellers
- C. using Intermig impellers
- D. all of the above Discuss
Correct Answer: using specially designed axial flow impellers
- 5. In aerobic microorganisms cultures radial flow impellers are used because
Options- A. they provide energy efficient high turbulent mixing conditions
- B. they provide low shear mixing conditions
- C. they provide high shear mixing conditions
- D. they ensure that bubble size is maximized leading to high oxygen transfer rates Discuss
Correct Answer: they provide high shear mixing conditions
- 6. A fermentation system has a KLa of 3 s-1 and a C0* of 5 ppm of O2. If the bulk liquid is saturated with oxygen then the oxygen transfer rate will be equal to
Options- A. zero
- B. 3 mg.l-1.s-1
- C. 5 mg.l-1.s-1
- D. 15 mg.l-1.s-1 Discuss
Correct Answer: zero
- 7. If the stirrer speed is too slow, bubbles will accumulate and coalescese under the impeller. This phenomenon is known as a
Options- A. coalesced impeller
- B. flooded impeller
- C. river impeller
- D. dry impeller Discuss
Correct Answer: flooded impeller
- 8. A reactor has a total volume of 50,000 litres. If it has a headspace volume of 10,000 litres, then volume of liquid in the reactor will be
Options- A. 10,000 l
- B. 20,000 l
- C. 30,000 l
- D. 40,000 l Discuss
Correct Answer: 40,000 l
- 9. Reynolds (Rei) number for the impeller is given by (where Di, stirrer diameter; N, stirrer speed, ?, density of fluid and ?, viscosity of fluid)
Options- A. DiV?/?
- B. Di2N?/?
- C. Di2V?/?
- D. DiN? /? Discuss
Correct Answer: Di2N?/?
- 10. The advantage of axial flow impellers over radial flow impellers is that axial flow impellers
Options- A. provide better lift of solids
- B. provide high shear conditions
- C. provide low shear conditions
- D. are cheaper to build Discuss
Correct Answer: provide better lift of solids
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