Agitation and Aeration MCQs

Question 1

Pure oxygen, if used instead of air will increase oxygen transfer rates because

Accepted Answer

the saturation concentration of oxygen is higher

Answer

the bubble size is smaller

Answer

the oxygen transfer coefficient is larger

Answer

the partial pressure of oxygen in the gas phase is lower

Question 2

For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (kL) co-relating power consumption (Pm) and fermenter volume (V) can be expressed as

Accepted Answer

kL ∝ (Pm/V)0.33

Answer

kL ∝ (Pm/V)0.66

Answer

kL ∝ (Pm/V)0.50

Answer

kL ∝ (Pm/V)

Question 3

Higher temperatures affect oxygen transfer rates by

Accepted Answer

increasing KLa but lowering C*o

Answer

lowering KLa but increasing C*o

Answer

increasing KLa and increasing Co

Answer

lowering KLa and lowering Co

Question 4

The Intermig impeller is

Accepted Answer

All of the above

Answer

an axial flow impeller which can be used for the culture of aerobic organisms

Answer

directed upwards rather than towards the base of the reactor

Answer

a fork shaped extensions to the impeller facilitate bubble break up

Question 5

Main reason for using baffles in stirred tank reactors are

Accepted Answer

both (a) and (b)

Answer

baffles permit turbulence conditions to arise at low stirrer speed

Answer

baffles will allow axial mixing to occur even with radial flow impellers

Answer

baffles prevent turbulent conditions in stirred tank reactors

Question 6

Which of the following is not classified as an axial flow impeller?

Accepted Answer

A Rushton turbine

Answer

A propeller

Answer

A marine impeller

Answer

A hydrofoil impeller

Question 7

Power number (Np) is also known as

Accepted Answer

Newton's number

Answer

Froude's number

Answer

Bond's number

Answer

Rayleigh's number

Question 8

Flooding is a condition/phenomenon which occur in a bioreactor when

Accepted Answer

The air escapes without being distributed by the agitator

Answer

The fermenter medium spills out the reactor due to foaming

Answer

The volume of foam is more than the volume of broth

Answer

None of the above

Question 9

A cylindrical reactor has a liquid volume of 100,000 litres. It has an aspect ratio the ratio of the channel height to width of 1:1. The height of the liquid in the reactor will be approximately:

Accepted Answer

5.0 m

Answer

1.0 m

Answer

3.0 m

Answer

7.0 m