Question is ⇒ Turbine impeller consists of flat impeller blades with, Options are ⇒ (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, (E) , Leave your comments or Download question paper.

Question is ⇒ Turbine impeller consists of flat impeller blades with, Options are ⇒ (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, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	Turbine impeller consists of flat impeller blades with
A.	a vertical pitch welded directly to the shaft [Wrong Answer]
B.	a angled pitch welded directly to the shaft [Wrong Answer]
C.	a vertical pitch welded to a horizontal disk [Correct Answer]
D.	a angled pitch welded to a horizontal disk [Wrong Answer]
View Answer 1 -3 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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⇒ A higher liquid height will lead to a higher gas hold up by which the oxygen transfer rate will be
higher throughout the reactor
lower throughout the reactor
higher at the base of the reactor
lower at the base of the reactor

⇒ 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

⇒ 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

⇒ The dynamic technique is based on the
oxygen material balance in an aerated batch fermenter during the growth of microorganisms
change of the oxygen concentration
oxidation of the sodium sulfite to sodium sulfate
oxygen material balance in a fermenter

⇒ For laminar flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Re_i is Reynolds number for agitator; D_i, stirrer diameter and N, stirrer speed)
N_p = K(Re_i)^-1
N_p = N²D_i(Re_i)^-1
N_p = K(Re_i)
N_p = KND_i(Re_i)^-2

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

⇒ Power number (N_p) is also known as
Froude's number
Bond's number
Newton's number
Rayleigh's number

⇒ The reason of using a flat disk in a Turbine is
to create high shear conditions
to break up bubbles more efficiently than the impeller blades
to ensure that the bulk of the energy consumption occurs at the blades
all of the above

⇒ During fermentation, the saturation concentration of oxygen was reduced from 7 ppm. to 1 ppm. Which one of the following conclusions can be drawn?
Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration
Microbial growth is not oxygen limited since the oxygen concentration is lesser than the saturation concentration
Experimental error leads to the reduction
No conclusion can be drawn

⇒ 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

⇒ 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
gas-liquid interface
bubble boundary layer
bulk liquid
gas phase

⇒ 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 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 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

⇒ 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

⇒ Which of the following model holds correct for the two-film theory? (where K_L is the mass transfer coefficient, D_AB diffusivity and Z_f film thickness)
K_L = D_AB/Z_f
K_L = D_AB
K_L = Z_f/D_AB
K_L = D_AB.Z_f

⇒ Which of the following stirrer requires least amount of energy for same yield?
Mig
Intermig
Turbine
Disc

⇒ The volume of liquid (V_L) in a cylindrical reactor can be calculated from the liquid height (H_L) and tank diameter (D_t) using the following equation
V_L = 4/3 x π x H_L x D_t³/8
V_L= H_L x π x D_t²/4
V_L= H_L x π x D_t²
V_L = 4 x π x D_t²

⇒ In the design of a paddle agitator, the ratio of paddle diameter to tank diameter is normally taken as
0.1
0.8
0.25
0.5

⇒ Which of the following is not considered among the three best-known theories of interphase mass transfer?
two-film theory
penetration theory
surface renewal theory
Calderbank and Moo-Young theory

⇒ For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (k_L) co-relating power consumption (P_m) and fermenter volume (V) can be expressed as
k_L ∝ (P_m/V)^0.33
k_L ∝ (P_m/V)^0.66
k_L ∝ (P_m/V)^0.50
k_L ∝ (P_m/V)

⇒ If the stirring speed increased from 300 to 500 rpm leads to an increase in the reaction rate by two folds. Then it may be concluded that
the reaction was mass transfer limited at 300 rpm
the reaction was mass transfer limited at 500 rpm
the reaction did not involve any mass transfer step
the movement of molecules in the reactor at 300 rpm occurred due to diffusion alone

⇒ The main function of the dimples provided in the cooling jacket is to
increase the level of turbulence of the cooling water in the jacket
increase the residence time of the cooling water in the jacket
increase the cooling water-jacket wall boundary layer size
all of the above

⇒ A flooded impeller will lead to poor oxygen transfer rates because
bubbles tend to coalesce under the impeller
bubbles tend to break down too rapidly under high shear conditions
bubbles tend to move too quickly through the bulk liquid
the cells clog up the surface of the bubble

⇒ A typical ceiling fan would be best described as a(n)
radial flow impeller
axial flow impeller
intermig impeller
Rushton turbine

⇒ 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

⇒ Power consumption by agitation is
a function of physical properties
a function of operating conditions
a function of vessel and impeller geometry
all of the above

⇒ 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

⇒ Why vortexing is undesirable in the agitation of biological systems?
The collision between the cells, impeller and air bubbles will lead to cell damage
Poor mixing despite the use of high stirrer speeds
Mixing will not be in the turbulent region
All of the above