Agitation and Aeration – Section 2

36. 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

A. 100%
B. 75%
C. 50%
D. 25%

Correct Answer: D. 25%

37. 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

A. zero
B. 3 mg.l-1.s-1
C. 5 mg.l-1.s-1
D. 15 mg.l-1.s-1

Correct Answer: A. zero

38. Which of the following would be best described as a radial flow impeller?

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

Correct Answer: B. A Rushton turbine

39. Small propellers turn at the speed of either

A. 20 or 150 rpm
B. 150 or 300 rpm
C. 400 or 800 rpm
D. 1150 rpm or 1750 rpm

Correct Answer: D. 1150 rpm or 1750 rpm

40. In aerobic microorganisms cultures radial flow impellers are used because

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

Correct Answer: C. they provide high shear mixing conditions

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