Agitation and Aeration problems
- 1. Which of the following would be best described as a radial flow impeller?
Options- A. An impeller with blades pitched at 45° to the vertical
- B. A Rushton turbine
- C. Both (a) and (b)
- D. An impeller which directs liquid flow towards the base of the reactor Discuss
Correct Answer: A Rushton turbine
- 2. Main reason for using baffles in stirred tank reactors are
Options- A. baffles permit turbulence conditions to arise at low stirrer speed
- B. baffles will allow axial mixing to occur even with radial flow impellers
- C. both (a) and (b)
- D. baffles prevent turbulent conditions in stirred tank reactors Discuss
Correct Answer: both (a) and (b)
- 3. Small propellers turn at the speed of either
Options- A. 20 or 150 rpm
- B. 150 or 300 rpm
- C. 400 or 800 rpm
- D. 1150 rpm or 1750 rpm Discuss
Correct Answer: 1150 rpm or 1750 rpm
- 4. A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen
Options- A. concentration is less than the critical concentration
- B. concentration is greater than the critical concentration
- C. levels are greater than the saturation concentration of oxygen
- D. levels are equal to saturation oxygen level Discuss
Correct Answer: concentration is less than the critical concentration
- 5. Which of the following model holds correct for the two-film theory? (where KL is the mass transfer coefficient, DAB diffusivity and Zf film thickness)
Options- A. KL = DAB/Zf
- B. KL = DAB
- C. KL = Zf/DAB
- D. KL = DAB.Zf Discuss
Correct Answer: KL = DAB/Zf
- 6. Higher temperatures affect oxygen transfer rates by
Options- A. increasing KLa but lowering C*o
- B. lowering KLa but increasing C*o
- C. increasing KLa and increasing Co
- D. lowering KLa and lowering Co Discuss
Correct Answer: increasing KLa but lowering C*o
- 7. In the design of a paddle agitator, the ratio of paddle diameter to tank diameter is normally taken as
Options- A. 0.1
- B. 0.8
- C. 0.25
- D. 0.5 Discuss
Correct Answer: 0.8
- 8. The maximum solubility of the alkane in the medium is 5 ppm. If the actual dissolved concentration of the alkane in the medium is 1 ppm. what conclusion may be drawn?
Options- A. The growth rate is limited by the rate of mass transfer of the alkane into the fermentation medium
- B. The growth rate is limited by the intrinsic kinetic properties of the cells and not by mass transfer
- C. The growth rate is neither mass transfer nor kinetically limited
- D. No conclusion on the growth rate can be withdrawn Discuss
Correct Answer: No conclusion on the growth rate can be withdrawn
- 9. The power required by an impeller in a gas sparged system compare to the power required by impeller operating at same speed in a gas free liquid is usually
Options- A. lesser
- B. higher
- C. same
- D. may be lesser or higher depending upon the geometry Discuss
Correct Answer: lesser
- 10. The oxygen absorption rate can be determined by
Options- A. sodium sulfite oxidation method
- B. dynamic gassing out technique
- C. direct measurement
- D. all of these Discuss
Correct Answer: all of these
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