Exercise: Agitation And Aeration

Questions for: Agitation And Aeration

The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that
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
Answer: C
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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
Answer: C
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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
Answer: D
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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
Answer: B
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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
Answer: A
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