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- Question
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
- Correct Answer
- provide better lift of solids
- 1. 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
- 2. 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
- 3. 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
- 4. 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
- 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
- 6. In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h-1, then the oxygen uptake will be
Options- A. 23 kg.h-1
- B. less than 23 kg.h-1
- C. greater than 23 kg.h-1
- D. 2.3 kg.h-1 Discuss
- 7. In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where Vs and Vt are the superficial gas velocity and bubble rise velocity)
Options- A. H = Vs/(Vs-Vt)
- B. H = Vs/(Vs+ Vt)
- C. H = Vs/(Vs.Vt)
- D. H = (Vs+Vt)/Vs Discuss
- 8. For turbulent flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Rei, is Reynolds number for agitator; Di, stirrer diameter and N, stirrer speed)
Options- A. Np = K(Rei)-1
- B. Np = N2Di(Rei)-1
- C. Np = K
- D. Can't be correlated Discuss
- 9. Which of the following will have the largest interfacial area per unit volume?
Options- A. A bubble with a diameter of 1 mm
- B. A bubble with a diameter of 5 mm
- C. A bubble with a diameter of 15 mm
- D. A bubble with a diameter of 50 mm Discuss
- 10. The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that
Options- A. a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime
- B. as the stirrer speed increases, the liquid will continue to circulate and then become turbulent
- C. as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
- D. A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate Discuss
Agitation and Aeration problems
Search Results
Correct Answer: Di2N?/?
Correct Answer: 40,000 l
Correct Answer: flooded impeller
Correct Answer: zero
Correct Answer: they provide high shear mixing conditions
Correct Answer: 23 kg.h-1
Correct Answer: H = Vs/(Vs+ Vt)
Correct Answer: Np = K
Correct Answer: A bubble with a diameter of 1 mm
Correct Answer: as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
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