200 Best MCQs on Agitation and aeration- biochemical engineering

Q65). Froude number is avoided in calculation of power requirements for low viscosity liquid mixing systems when

a).baffled systems are used
b).Reynolds number is less than 300
c).both (a)and(b)
d).none of these

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


Q66). 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).1
b).0.75
c).0.5
d).0.25

Correct Answer:
0.25
Explaination:


Q67). 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:
A Rushton turbine
Explaination:


Q68). 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:
1150 rpm or 1750 rpm
Explaination:


Q69). 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:
they provide high shear mixing conditions
Explaination:


Q70). 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:
as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
Explaination:


Q71). Turbulent flow range of mixing speed is obtained for

a).Rei<10
b).10c).Rei>10^4
d).None of these

Correct Answer:
Rei>10^4
Explaination:


Q72). Axial flow impellers

a).provide high shear conditions for breaking up bubbles
b).provide low shear conditions and are suited for use in shear sensitive procesess
c).provide direct flow towards the walls of the reactor
d).none of the above

Correct Answer:
provide low shear conditions and are suited for use in shear sensitive procesess
Explaination:


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