Question is ⇒ In the bubble boundary layer, oxygen concentration can be determined by measuring, Options are ⇒ (A) the steady state oxygen concentration in a mixed aerated reactor before inoculation, (B) the steady state oxygen concentration in a mixed aerated reactor after inoculation, (C) the steady state oxygen concentration in the boundary layer using a micro-probe, (D) volume of oxygen supplied, (E) , Leave your comments or Download question paper.

Question is ⇒ In the bubble boundary layer, oxygen concentration can be determined by measuring, Options are ⇒ (A) the steady state oxygen concentration in a mixed aerated reactor before inoculation, (B) the steady state oxygen concentration in a mixed aerated reactor after inoculation, (C) the steady state oxygen concentration in the boundary layer using a micro-probe, (D) volume of oxygen supplied, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In the bubble boundary layer, oxygen concentration can be determined by measuring
A.	the steady state oxygen concentration in a mixed aerated reactor before inoculation [Correct Answer]
B.	the steady state oxygen concentration in a mixed aerated reactor after inoculation [Wrong Answer]
C.	the steady state oxygen concentration in the boundary layer using a micro-probe [Wrong Answer]
D.	volume of oxygen supplied [Wrong Answer]
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⇒ 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)

⇒ The average fractional gas hold up (H) can be given as (where Z_f and Z_l are the level of aerated and clear liquid respectively)
H = (Z_f-Z_l)/Z_f
H = Z_f/Z_l
H = Z_f/Z_fZ_l
H =(Z_f+Z_l)/Z_f

⇒ 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

⇒ Which of the following would be best described as an axial flow impeller?
An impeller with blades pitched at 45° to the vertical
An impeller which directs liquid flow towards the base of the reactor
Both (a) and (b)
An impeller with blades pitched at 75° to the vertical

⇒ 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

⇒ Vortexing in stirred tank reactors can be prevented by
installing baffles in the reactor
shifting the impeller to an off-centre position
Both (a) and (b)
using axial flow impellers

⇒ 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

⇒ A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen
concentration is less than the critical concentration
concentration is greater than the critical concentration
levels are greater than the saturation concentration of oxygen
levels are equal to saturation oxygen level

⇒ 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

⇒ Swirling and vortex formation can be prevented by
using baffles
using diffusion ring with turbines
both (a) and (b)
none of these

⇒ An aerated bioreactor will increase oxygen transfer rates with the addition of detergents because it
enhances bubble coalescence
causes bubbles to expand
discourages bubble coalescence
increases the surface tension of the liquid

⇒ In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where V_s and V_t are the superficial gas velocity and bubble rise velocity)
H = V_s/(V_s-V_t)
H = V_s/(V_s+ V_t)
H = V_s/(V_s.V_t)
H = (V_s+V_t)/V_s

⇒ 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

⇒ 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

⇒ An increase in the heat transfer in the stirred tank reactor will be observed at
higher cooling water temperature
higher stirrer speed
the removal of baffles from the reactor
slower stirrer speed

⇒ Which device is commonly used for measuring the rate of rotation (rpm) of the stirrer shaft?
Anemometer
Manometer
Tachometer
Barometer

⇒ Higher temperatures affect oxygen transfer rates by
increasing K_La but lowering C^*_o
lowering K_La but increasing C^*_o
increasing K_La and increasing C_o
lowering K_La and lowering C_o

⇒ 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

⇒ The oxygen transfer rate in a bioreactor will increase if
oil is added
antifoam is added
detergent like molecules are added
increase in the reactor temperature

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

⇒ 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

⇒ The maximum solubility of the alkane in the medium is 5 ppm. If the actual dissolved concentration of the alkane in the medium is 1 ppm. what conclusion may be drawn?
The growth rate is limited by the rate of mass transfer of the alkane into the fermentation medium
The growth rate is limited by the intrinsic kinetic properties of the cells and not by mass transfer
The growth rate is neither mass transfer nor kinetically limited
No conclusion on the growth rate can be withdrawn

⇒ 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

⇒ 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

⇒ In the bubble boundary layer, oxygen concentration can be determined by measuring
the steady state oxygen concentration in a mixed aerated reactor before inoculation
the steady state oxygen concentration in a mixed aerated reactor after inoculation
the steady state oxygen concentration in the boundary layer using a micro-probe
volume of oxygen supplied

⇒ 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

⇒ Flooding is a condition/phenomenon which occur in a bioreactor when
The air escapes without being distributed by the agitator
The fermenter medium spills out the reactor due to foaming
The volume of foam is more than the volume of broth
None of the above

⇒ For turbulent 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 = N²Di(Re_i)^-1
N_p = K
Can't be correlated

⇒ Which of the following number is calculated from the diameter and peripheral speed of the impeller?
Reynolds number
Froude number
Power number
None of these

⇒ 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