Agitation and Aeration – Section 3

1. 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

Correct Answer: C. as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.

2. Turbulent flow range of mixing speed is obtained for

A. Rei<10
B.10<Rei<104
C. Rei>104
D. None of these

Correct Answer: C. Rei>104

3. For laminar 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)

A.Np= K(Rei)-1
B.Np= N2Di(Rei)-1
C.Np= K(Rei)
D.Np= KNDi(Rei)-2

Correct Answer: A.Np= K(Rei)-1

4. 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)

A. Np= K(Rei)-1
B. Np= N2Di(Rei)-1
C. Np= K
D. Can’t be correlated

Correct Answer: C. Np= K

5. In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h-1, then the oxygen uptake will be

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

Correct Answer: A. 23 kg.h-1

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