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Agitation and Aeration MCQ Questions & Answers

Agitation and Aeration MCQs : This section focuses on the "Agitation and Aeration". These Multiple Choice Questions (MCQs) should be practiced to improve the Agitation and Aeration skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.




Question 1

The range of width for the baffle in the fermenter is __________ times of vessel diameter

A. 1/10 to 1/12
B. 1/8 to 1/10
C. 1/5 to 1/8
D. none of these

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Question 2

Power number is ratio of

A. imposed forced to intertial force
B. bouyant force to inertial force
C. gravitation force to inertial force
D. imposed force to gravitational force

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Question 3

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

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Question 4

Vortexing in stirred tank reactors can be prevented by

A. installing baffles in the reactor
B. shifting the impeller to an off-centre position
C. Both (a) and (b)
D. using axial flow impellers

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Question 5

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

A. 01:03
B. 02:01
C. 04:01
D. 01:05

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Question 6

Which of the following impellers will provide radial flow?

A. Paddles
B. Flat blade turbines
C. Disk flat blade turbines
D. All of the above

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Question 7

Power consumption by agitation is

A. a function of physical properties
B. a function of operating conditions
C. a function of vessel and impeller geometry
D. all of the above

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Question 8

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

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Question 9

The range of width for the baffle in the fermenter is __________ times of vessel diameter

A. 1/10 to 1/12
B. 1/8 to 1/10
C. 1/5 to 1/8
D. None of these

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Question 10

Which of the following impellers are used for wide range of viscosities?

A. paddles
B. turbines
C. propellers
D. None of the above

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Question 11

Penetration theory assumes that turbulent eddies travel from the bulk of the phase to the interface where they remain constant for a constant exposure time (te). The model correlating KL, mass transfer coefficient and DAB, diffusivity can be expressed as

A. KL = 2(DAB/πte)0.25
B. KL = 2(DAB/πte)0.5
C. KL = 2(DAB/πte)0.75
D. KL = 2(DAB/πte)

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Question 12

A typical ceiling fan would be best described as a(n)

A. radial flow impeller
B. axial flow impeller
C. intermig impeller
D. Rushton turbine

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Question 13

Transient flow range of mixing speed is obtained for

A. Rei<10
B. 10C. Rei>10^4
D. None of the above

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Question 14

The oxygen transfer rate in a bioreactor will increase if

A. oil is added
B. antifoam is added
C. detergent like molecules are added
D. increase in the reactor temperature

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Question 15

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

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Question 16

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

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Question 17

Surface renewal theory predicts that the mass transfer coefficient is

A. directly proportional to the square root of the molecular diffusivity
B. inversely proportional to the square root of the molecular diffusivity
C. directly proportional to the cube root of the molecular diffusivity
D. indirectly proportional to the cube root of the molecular diffusivity

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Question 18

Swirling and vortex formation can be prevented by

A. using baffles
B. using diffusion ring with turbines
C. both (a) and (b)
D. none of these

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Question 19

Which of the following type(s) of stirrer can be used for microbiological processes?

A. Mig
B. Intermig
C. Turbine
D. All of the above

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Question 20

The power consumption in a stirring vessel can be assessed by using a

A. dynamometer
B. strain gauge attached to agitator shaft
C. watt meter attached to agitator motor
D. all of these

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Question 21

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)

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Question 22

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

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Question 23

Which of the following impellers are used for wide range of viscosities?

A. paddles
B. turbines
C. propellers
D. none of these

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Question 24

Swirling and vortex formation can be prevented by

A. using baffles
B. using diffusion ring with turbines
C. Both A and B
D. None of the above

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Question 25

Why vortexing is undesirable in the agitation of biological systems?

A. The collision between the cells, impeller and air bubbles will lead to cell damage
B. Poor mixing despite the use of high stirrer speeds
C. Mixing will not be in the turbulent region
D. All of the above

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Question 26

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

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Question 27

Which have the maximum resistance while transferring carbon dioxide from the bulk liquid to an air bubble?

A. Moving through the gas liquid interface
B. Moving through the bubble boundary layer
C. Moving across the cell membrane
D. Moving through the bulk liquid

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Question 28

Which of the following(s) is/are non-mechanically agitated reactors?

A. Stirrer tank reactor
B. Bubble column
C. Air lift reactor
D. Both (b) and (c)

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Question 29

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

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Question 30

Which of the following type(s) of stirrer can be used for microbiological processes?

A. Mig
B. Intermig
C. Turbine
D. All of these

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Question 31

Transient flow range of mixing speed is obtained for

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

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Question 32

Power number is expressed as

A. P0 / N2Di3ρ
B. P0 / N3Di5ρ
C. P0 / N3Di3ρ
D. P0 / N2Di2ρ

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Question 33

If liquid density and viscosity remains constant, then the Reynolds number in a stirred tank reactor will vary with the

A. impeller diameter
B. square root of the impeller diameter
C. square of the impeller diameter
D. cube of the impeller diameter

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Question 34

Henry's law relates

A. the partial pressure of oxygen and the saturation concentration of oxygen in the liquid
B. the oxygen transfer rate and the bubble size
C. the oxygen transfer rate and the temperature
D. the oxygen transfer rate to the partial pressure of oxygen in the liquid

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Question 35

Radial flow impellers

A. provide high shear conditions for breaking up bubbles
B. direct flow towards the walls of the reactor
C. Both (a) and (b)
D. provide low shear conditions and are suited for use in shear sensitive procesess

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Question 36

Radial flow impellers

A. provide high shear conditions for breaking up bubbles
B. direct flow towards the walls of the reactor
C. Both A and B
D. provide low shear conditions and are suited for use in shear sensitive procesess

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Question 37

What is the ratio of depth of liquid in vessel to the diameter of tank (H:Dt)?

A. 1 : 1
B. 2 : 1
C. 4 : 1
D. None of the above

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Question 38

Which of the following will have the highest surface area available for oxygen transfer?

A. A shake flask
B. A standing test tube
C. A non-sparged stirred tank reactor agitated at 400 rpm
D. A sparged stirred tank reactor agitated at 400 rpm

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Question 39

A flooded impeller will lead to poor oxygen transfer rates because

A. bubbles tend to coalesce under the impeller
B. bubbles tend to break down too rapidly under high shear conditions
C. bubbles tend to move too quickly through the bulk liquid
D. the cells clog up the surface of the bubble

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Question 40

The average concentration of oxygen in the boundary layers surrounding the bubbles (Co*) in a reactor is normally determined by

A. ultra-small dissolved oxygen probes
B. laser based photographic systems
C. measuring the steady state concentration of oxygen in the bulk liquid prior to inoculation of the reactor
D. measuring the steady state concentration of oxygen in the bulk liquid after inoculation of the reactor

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Question 41

The average fractional gas hold up (H) can be given as (where Zf and Zl are the level of aerated and clear liquid respectively)

A. H = (Zf-Zl)/Zf
B. H = Zf/Zl
C. H = Zf/ZfZl
D. H =(Zf+Zl)/Zf

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Question 42

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

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Question 43

When liquid is pumped through cooling coil in a stirred tank reactor to cool. Which of the following is not correct?

A. If the stirrer speed is increased, the rate will be faster
B. Baffles in the tank will increase the rate of cooling
C. Faster cooling rates at a slower rate of pumping
D. Faster cooling rates at a faster rate of pumping

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Question 44

What is the ratio of depth of liquid in vessel to the diameter of tank (H:Dt)?

A. 01:01
B. 02:01
C. 04:01
D. none of these

View Answer

Question 45

The power consumption in a stirring vessel can be assessed by using a

A. dynamometer
B. strain gauge attached to agitator shaft
C. watt meter attached to agitator motor
D. All of the above

View Answer

Question 46

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

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Question 47

The volume of liquid (VL) in a cylindrical reactor can be calculated from the liquid height (HL) and tank diameter (Dt) using the following equation

A. VL = 4/3 x π x HL x Dt3/8
B. VL= HL x π x Dt2/4
C. VL= HL x π x Dt2
D. VL = 4 x π x Dt2

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Question 48

Which of the following would be best described as an axial flow impeller?

A. An impeller with blades pitched at 45° to the vertical
B. An impeller which directs liquid flow towards the base of the reactor
C. Both (a) and (b)
D. An impeller with blades pitched at 75° to the vertical

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Question 49

The oxygen uptake requirements of a microbial population is characterized by the following parameters: μm = 0.2 h-1, K0 = 0.2 mg O2.l-1, Y0 = 0.5 mg dry weight/mg O2 and C0,crit=0.8 mg.l-1 The required concentration of cells is 1000 mg.l-1 and the saturation oxygen concentration of the medium is 5.8 mg.l-1. The required KLa must be greater than

A. 64 h-1
B. 32 h-1
C. 16 h-1
D. 8h-1

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Question 50

Which of the following best explains the reasons for using axial flow impellers in crystallization and precipitation reactions?

A. Crystal and precipitates are not too small, so as to ensure easy separation of the solids from the mother liquor
B. Crystals and precipitates are thoroughly broken down, so as to ensure easy separation of the solids from the mother liquor
C. Both (a) and (b)
D. Axial flow impellers provide low shear, energy efficient mixing conditions

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Question 51

The rate limiting step in the movement of oxygen from the gas phase in a bubble to the cell is the movement of oxygen molecules through

A. gas-liquid interface
B. bubble boundary layer
C. bulk liquid
D. gas phase

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