Biochemical Engineering - Agitation and Aeration

Exercise :: Agitation and Aeration - Section 2

26. 

During fermentation, the saturation concentration of oxygen was reduced from 7 ppm. to 1 ppm. Which one of the following conclusions can be drawn?

A. Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration
B. Microbial growth is not oxygen limited since the oxygen concentration is lesser than the saturation concentration
C. Experimental error leads to the reduction
D. No conclusion can be drawn

Answer: Option D

Explanation:

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27. 

If the stirrer speed is too slow, bubbles will accumulate and coalescese under the impeller. This phenomenon is known as a

A. coalesced impeller
B. flooded impeller
C. river impeller
D. dry impeller

Answer: Option B

Explanation:

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28. 

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?

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D. No conclusion on the growth rate can be withdrawn

Answer: Option D

Explanation:

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29. 

Reynolds (Rei) number for the impeller is given by (where Di, stirrer diameter; N, stirrer speed, ρ, density of fluid and μ, viscosity of fluid)

A. Di
B. Di2
C. Di2
D. Di

Answer: Option B

Explanation:

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30. 

The advantage of axial flow impellers over radial flow impellers is that axial flow impellers

A. provide better lift of solids
B. provide high shear conditions
C. provide low shear conditions
D. are cheaper to build

Answer: Option A

Explanation:

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