Question is ⇒ Vortexing in stirred tank reactors can be prevented by, Options are ⇒ (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, (E) , Leave your comments or Download question paper.

Question is ⇒ Vortexing in stirred tank reactors can be prevented by, Options are ⇒ (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, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	Vortexing in stirred tank reactors can be prevented by
A.	installing baffles in the reactor [Wrong Answer]
B.	shifting the impeller to an off-centre position [Wrong Answer]
C.	Both (a) and (b) [Correct Answer]
D.	using axial flow impellers [Wrong Answer]
View Answer 1 -4 Explanation:- Answer : C Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

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⇒ Which have the maximum resistance while transferring carbon dioxide from the bulk liquid to an air bubble?
Moving through the gas liquid interface
Moving through the bubble boundary layer
Moving across the cell membrane
Moving through the bulk liquid

⇒ Henry's law relates
the partial pressure of oxygen and the saturation concentration of oxygen in the liquid
the oxygen transfer rate and the bubble size
the oxygen transfer rate and the temperature
the oxygen transfer rate to the partial pressure of oxygen in the liquid

⇒ 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:
1.0 m
3.0 m
5.0 m
7.0 m

⇒ Laminar flow range of mixing speed is obtained for
Re_i<10
10<Re_i<10⁴
Re_i>10⁴
None of these

⇒ A cylindrical reactor fitted with Rushton Turbine has a liquid volume of 100,000 litres. It has an aspect ratio (the ratio of the channel height to the width) of 2:1. The diameter of the impeller should be approximately:
1.3 m
3.3 m
5.3 m
7.3 m

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

⇒ A fermentation system has a K_La of 3 s^-1 and a C₀* of 5 ppm of O₂. If the bulk liquid is completely depleted of oxygen, then the oxygen transfer rate will be equal to
zero
15 mg.l^-1.s^-1
10 mg.l^-1.s^-1
5 mg.l^-1.s^-1

⇒ Gas hold up, characterizing the hydrodynamics in a fermenter, mainly depends on the
superficial gas velocity
power consumption
Both (a) and (b)
gas concentration

⇒ Pure oxygen, if used instead of air will increase oxygen transfer rates because
the saturation concentration of oxygen is higher
the bubble size is smaller
the oxygen transfer coefficient is larger
the partial pressure of oxygen in the gas phase is lower

⇒ Which of the following impellers are used for wide range of viscosities?
paddles
turbines
propellers
none of these

⇒ The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that
a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime
as the stirrer speed increases, the liquid will continue to circulate and then become turbulent
as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate

⇒ Which of the following is correct for the off-centre impellers?
Off-centre impellers can be used with any size reactor
Off-centre impellers should only be used with reactors with volumes less than 10 m³
The impeller should never be placed in an off-centre position
Off-centre impellers can be used when volume is greater than 10 m³

⇒ Which of the following is most likely to cause an increase in the rate of oxygen transfer into a particular aerated fermentation system?
Addition of antifoams
Increase in temperature
Increase in stirrer speed
Both (a) and (b)

⇒ The power required by an agitator operating in a gas-sparged system is
lesser than the power required by an impeller in operating at same speed in a gas free system
more than the power required by an impeller in operating at same speed in a gas free system
same as the power required by an impeller in operating at same speed in a gas free system
none of the above

⇒ Power number is ratio of
imposed forced to intertial force
bouyant force to inertial force
gravitation force to inertial force
imposed force to gravitational force

⇒ The oxygen uptake requirements of a microbial population is characterized by the following parameters: μ_m= 0.2 h^-1, K₀ = 0.2 mg O₂.l^-1, Y₀ = 0.5 mg dry weight/mg O₂ and C_0,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 K_La must be greater than
64 h^-1
32 h^-1
16 h^-1
8h^-1

⇒ The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams
increase the tendency of bubbles to coalesce
tend to accumulate in the gas liquid interface
reduce the surface tension of the liquid
All of the above answers

⇒ Detergent like substances produced by microorganisms during a fermentation will lead to
decrease the surface tension of the liquid
accumulate at the gas liquid interface
decrease the rate of bubble coalescence
all of the above

⇒ Which of the following would be best described as a radial flow impeller?
An impeller with blades pitched at 45° to the vertical
A Rushton turbine
Both (a) and (b)
An impeller which directs liquid flow towards the base of the reactor

⇒ Which of the following is not classified as an axial flow impeller?
A propeller
A marine impeller
A Rushton turbine
A hydrofoil impeller

⇒ Which of the following will have the highest surface area available for oxygen transfer?
A shake flask
A standing test tube
A non-sparged stirred tank reactor agitated at 400 rpm
A sparged stirred tank reactor agitated at 400 rpm

⇒ To increase the oxygen transfer rate in a shake flask culture system, which of the following (s) is/are followed?
Liquid volume in the flask is reduced
Stirrer speed is increased
Baffled flasks are used
All of the above

⇒ 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 (t_e). The model correlating K_L, mass transfer coefficient and D_AB, diffusivity can be expressed as
K_L = 2(D_AB/πt_e)^0.25
K_L = 2(D_AB/πt_e)^0.5
K_L = 2(D_AB/πt_e)^0.75
K_L = 2(D_AB/πt_e)

⇒ When the height of an aerated bioreactor is increased, it will increase the oxygen transfer rate by
increasing the partial pressure of oxygen at the base of the reactor
decreasing the saturation concentration of oxygen in the reactor
decreasing the gas-holdup
all of the above

⇒ In aerobic microorganisms cultures radial flow impellers are used because
they provide energy efficient high turbulent mixing conditions
they provide low shear mixing conditions
they provide high shear mixing conditions
they ensure that bubble size is maximized leading to high oxygen transfer rates

⇒ The power consumption in a stirring vessel can be assessed by using a
dynamometer
strain gauge attached to agitator shaft
watt meter attached to agitator motor
all of these

⇒ Larger propellers turn at the speed of
20 to 150 rpm
150 to 300 rpm
400 to 800 rpm
1150 rpm

⇒ What is the effect of the concentration of dissolved salts and sugars on the oxygen transfer rate?
The saturation concentration of oxygen in the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
The K_La of the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
The K_La of the medium increases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
None of the above

⇒ Axial flow impellers
provide high shear conditions for breaking up bubbles
provide low shear conditions and are suited for use in shear sensitive procesess
provide direct flow towards the walls of the reactor
none of the above

⇒ Which of the following impellers generate a flow parallel to the axis of shaft?
Axial flow
Radial flow
Both (a)and(b)
None of these