200 Best MCQs on Agitation and aeration- biochemical engineering

Q17). What is the ratio of diameter of impeller to the diameter of tank (Da:Dt)?

a). 1:3
b). 2:1`
c). 4:1
d). 1:5

Correct Answer:
1:3
Explaination:


Q18). The reason of using a flat disk in a Turbine is

a).to create high shear conditions
b).to break up bubbles more efficiently than the impeller blades
c).to ensure that the bulk of the energy consumption occurs at the blades
d).all of the above

Correct Answer:
to ensure that the bulk of the energy consumption occurs at the blades
Explaination:


Q19). Which of the following is not considered among the three best-known theories of interphase mass transfer?

a).two-film theory
b).penetration theory
c).surface renewal theory
d).Calderbank and Moo-Young theory

Correct Answer:
Calderbank and Moo-Young theory
Explaination:


Q20). Which of the following is most likely to cause an increase in the rate of oxygen transfer into a particular aerated fermentation system?

a).Addition of antifoams
b).Increase in temperature
c).Increase in stirrer speed
d).Both (a) and (b)

Correct Answer:
Increase in stirrer speed
Explaination:


Q21). At 25°C, the saturation concentration of oxygen in water is 1.26 mmol/l and the partial pressure of oxygen is 1 atm. The Henry’s law constant will be

a).0.793atml/mmol
b).0.207atml/mmol
c).1.26 atml/mmol
d).8.74 atml/mmol

Correct Answer:
0.793atml/mmol
Explaination:


Q22). Gas hold up, characterizing the hydrodynamics in a fermenter, mainly depends on the

a).superficial gas velocity
b).power consumption
c).Both (a) and (b)
d).gas concentration

Correct Answer:
Both (a) and (b)
Explaination:


Q23). Turbine impeller consists of flat impeller blades with

a).a vertical pitch welded directly to the shaft
b).a angled pitch welded directly to the shaft
c).a vertical pitch welded to a horizontal disk
d).a angled pitch welded to a horizontal disk

Correct Answer:
a vertical pitch welded to a horizontal disk
Explaination:


Q24). An aerated bioreactor will increase oxygen transfer rates with the addition of detergents because it

a).enhances bubble coalescence
b).causes bubbles to expand
c).discourages bubble coalescence
d).increases the surface tension of the liquid

Correct Answer:
discourages bubble coalescence
Explaination:


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