Agitation and Aeration problems
- 1. Froude number is avoided in calculation of power requirements for low viscosity liquid mixing systems when
Options- A. baffled systems are used
- B. Reynolds number is less than 300
- C. both (a)and(b)
- D. none of these Discuss
Correct Answer: both (a)and(b)
- 2. Larger propellers turn at the speed of
Options- A. 20 to 150 rpm
- B. 150 to 300 rpm
- C. 400 to 800 rpm
- D. 1150 rpm Discuss
Correct Answer: 400 to 800 rpm
- 3. What is/are the major difference(s) between disc and turbine type stirrer?
Options- A. Blades in disc type are projected out beyond the edge of disc while blades are curved one in turbine type
- B. Turbine type requires 50 % less air than disc type for the same yield and energy consumption
- C. Both (a) and (b)
- D. Number of blades in the stirrer Discuss
Correct Answer: Both (a) and (b)
- 4. In the bubble boundary layer, oxygen concentration can be determined by measuring
Options- A. the steady state oxygen concentration in a mixed aerated reactor before inoculation
- B. the steady state oxygen concentration in a mixed aerated reactor after inoculation
- C. the steady state oxygen concentration in the boundary layer using a micro-probe
- D. volume of oxygen supplied Discuss
Correct Answer: the steady state oxygen concentration in a mixed aerated reactor before inoculation
- 5. The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams
Options- A. increase the tendency of bubbles to coalesce
- B. tend to accumulate in the gas liquid interface
- C. reduce the surface tension of the liquid
- D. All of the above answers Discuss
Correct Answer: All of the above answers
- 6. The dynamic technique is based on the
Options- A. oxygen material balance in an aerated batch fermenter during the growth of microorganisms
- B. change of the oxygen concentration
- C. oxidation of the sodium sulfite to sodium sulfate
- D. oxygen material balance in a fermenter Discuss
Correct Answer: oxygen material balance in an aerated batch fermenter during the growth of microorganisms
- 7. During aeration, a cylindrical reactor had a height of 10 m. Without aeration, the height was 7.5 m. Under these aeration and mixing conditions, the gas hold up in the reactor is
Options- A. 100%
- B. 75%
- C. 50%
- D. 25% Discuss
Correct Answer: 25%
- 8. A cylindrical reactor has a liquid volume of 100,000 litres. It has an aspect ratio the ratio of the channel height to width of 1:1. The height of the liquid in the reactor will be approximately:
Options- A. 1.0 m
- B. 3.0 m
- C. 5.0 m
- D. 7.0 m Discuss
Correct Answer: 5.0 m
- 9. When the height of an aerated bioreactor is increased, it will increase the oxygen transfer rate by
Options- A. increasing the partial pressure of oxygen at the base of the reactor
- B. decreasing the saturation concentration of oxygen in the reactor
- C. decreasing the gas-holdup
- D. all of the above Discuss
Correct Answer: increasing the partial pressure of oxygen at the base of the reactor
- 10. Power number (Np) is also known as
Options- A. Froude's number
- B. Bond's number
- C. Newton's number
- D. Rayleigh's number Discuss
Correct Answer: Newton's number
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