Biochem - Agitation and Aeration [S1] Flashcards
1
Q
- Swirling and vortex formation can be prevented by
A
- Using baffles
2
Q
- Power number is expressed as
A
- P0N3D02PN3D02PP0
3
Q
- The power consumption in a stirring vessel can be assessed by using a
A
- All of these
4
Q
- Surface renewal theory predicts that the mass transfer coefficient is
A
- Directly proportional to the square root of the molecular diffusivity
5
Q
- The oxygen transfer rate in a bioreactor will increase if
A
- Detergent-like molecules are added
6
Q
- Which of the following impellers are used for wide range of viscosities?
A
- Turbines
7
Q
- Which of the following type(s) of stirrer can be used for microbiological processes?
A
- All of these
8
Q
- The range of width for the baffle in the fermenter is times of vessel diameter.
A
- 1/10 to 1/12
9
Q
- The average concentration of oxygen in the boundary layers surrounding the bubbles (C0C0) in a reactor is normally determined by
A
- Measuring the steady state concentration of oxygen in the bulk liquid prior to inoculation of the reactor
10
Q
- Why vortexing is undesirable in the agitation of biological systems?
A
- All of the above
11
Q
- 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
- Bubble boundary layer
12
Q
- 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 (tctc). The model correlationKLKLmass transfer coefficient andDABDAB, diffusivity can be expressed as
A
- KL=2(DABπtc)0.50KL=2(πtcDAB)0.50
13
Q
- The oxygen uptake requirements of a microbial population is characterized by the following parameters:μm=0.2 h−1μm=0.2h−1,K0=0.2 mgO2 L−1K0=0.2mgO2L−1,Y0=0.5 mgdryweight/mgO2Y0=0.5mgdryweight/mgO2andCocrit=0.8 mgL−1Cocrit=0.8mgL−1. The required concentration of cells is 1000 mg L−1−1and the saturation oxygen concentration of the medium is 5.8 mg L−1−1. The requiredKLaKLamust be greater than
A
- 64 h-1
14
Q
- Which have the maximum resistance while transferring carbon dioxide from the bulk liquid to an air bubble?
A
- Moving through the bubble boundary layer
15
Q
- If liquid density and viscosity remains constant, then the Reynolds number in a stirred tank reactor will vary with the
A
- Square of the impeller diameter
16
Q
- What is the ratio of depth of liquid in vessel to the diameter of tank (H:Dii)?
A
- 2:1
17
Q
- Radial flow impellers
A
- Both (a) and (b)
18
Q
- Transient flow range of mixing speed is obtained for
A
- 10<Ret<10410<Ret<104
19
Q
- A typical ceiling fan would be best described as a(n)
A
- Axial flow impeller
20
Q
- What is the ratio of diameter of impeller to the diameter of tank (Dss:Dii)?
A
- 1:3
21
Q
- The reason of using a flat disk in a Turbine is
A
- All of the above
22
Q
- Which of the following is not considered among the three best-known theories of interphase mass transfer?
A
- Calderbank and Moo-Young theory
23
Q
- Which of the following is most likely to cause an increase in the rate of oxygen transfer into a particular aerated fermentation system?
A
- Increase in stirrer speed
24
Q
- 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
- 0.793 atm-L/mmol
25
Q
- Gas hold up, characterizing the hydrodynamics in a fermenter, mainly depends on the
A
- Both (a) and (b)
26
Q
- Turbine impeller consists of flat impeller blades with
A
- A vertical pitch welded to a horizontal disk
27
Q
- An aerated bioreactor will increase oxygen transfer rates with the addition of detergents because it
A
- Discourages bubble coalescence
28
Q
- Vortexing in stirred tank reactors can be prevented by
A
- Both (a) and (b)
29
Q
- Which of the following would be best described as an axial flow impeller?
A
- Both (a) and (b)
30
Q
- Henry’s law relates
A
- The partial pressure of oxygen and the saturation concentration of oxygen in the liquid
31
Q
- Power number is ratio of
A
- Imposed forced to inertial force
32
Q
- The volume of liquid (VL) in a cylindrical reactor can be calculated from the liquid height (HL) and tank diameter (Dtt) using the following equation.
A
- VL=HL×π×Dt24VL=HL×π×4Dt2
33
Q
- The average fractional gas hold up (H) can be given as (where Zffand Zllare the level of aerated and clear liquid respectively)
A
- H=(Zf−Zl)/ZfH=(Zf−Zl)/Zf
34
Q
- Which of the following(s) is/are non-mechanically agitated reactors?
A
- Both (b) and (c)
35
Q
- Which of the following best explains the reasons for using axial flow impellers in crystallization and precipitation reactions?
A
- Axial flow impellers provide low shear, energy efficient mixing conditions
36
Q
- Which of the following will have the highest surface area available for oxygen transfer?
A
- A sparge stirred tank reactor agitated at 400 rpm
37
Q
- A flooded impeller will lead to poor oxygen transfer rates because
A
- Bubbles tend to coalesce under the impeller
38
Q
- Power consumption by agitation is
A
- All of the above
39
Q
- Which of the following impellers will provide radial flow?
A
- All of the above
40
Q
- When liquid is pumped through cooling coil in a stirred tank reactor to cool. Which of the following is not correct?
A
- Faster cooling rates at a slower rate of pumping
