Biochem - Agitation and Aeration [S2] Flashcards
(40 cards)
1
Q
- When the height of an aerated bioreactor is increased it will increase the oxygen transfer rate by
A
- Increasing the partial pressure of oxygen at the base of the reactor
2
Q
- Which of the following is correct for the off-center impellers?
A
- Off-center impellers should only be used with reactors with volumes less than 10 m3
3
Q
- The power required by an impeller in a gas sparged system compared to the power required by the impeller operating at same speed in a gas free liquid is usually
A
- Lesser
4
Q
- Which of the following stirrer requires least amount of energy for same yield?
A
- Intermig
5
Q
- A reactor has a total volume of 50,000 liters. If it has a headspace volume of 10,000 liters, then volume of liquid in the reactor will be
A
- 40,000 L
6
Q
- Pure oxygen, if used instead of air will increase oxygen transfer rates because
A
- The saturation concentration of oxygen is higher
7
Q
- For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (kLL) corelating power consumption (PmPmand fermenter volume (V) can be expressed as
A
- kL∝(Pmv)0.33kL∝(vPm)0.33
8
Q
- Higher temperatures affect oxygen transfer rates by
A
- Increasing K1a but lowering C0
9
Q
- The Intermig impeller is
A
- All of the above
10
Q
- Main reason for using baffles in stirred tank reactors are
A
- Both (a) and (b)
11
Q
- Which of the following is not classified as an axial flow impeller?
A
- A Rushton turbine
12
Q
- Power number (Npp) is also known as
A
- Newton’s number
13
Q
- Flooding is a condition/phenomenon which occur in a bioreactor when
A
- The air escapes without being distributed by the agitator
14
Q
- A cylindrical reactor has a liquid volume of 100,000 liters. 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:
A
- 5.0 m
15
Q
- Detergent like substances produced by microorganisms during a fermentation will lead to
A
- All of the above
16
Q
- A cylindrical reactor fitted with Rushton Turbine has a liquid volume of 100,000 liters. 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:
A
- 3.3 m
17
Q
- 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
18
Q
- Impeller damage can be minimized by
A
- All of the above
19
Q
- To increase the oxygen transfer rate in a shake flask culture system, which of the following (s) is/are followed?
A
- All of the above
20
Q
- What is/are the major difference(s) between disc and turbine type stirrer?
A
- Both (a) and (b)
21
Q
- In the design of a paddle agitator, the ratio of paddle diameter to tank diameter is normally taken as
A
- 0.5
22
Q
- The oxygen absorption rate can be determined by
A
- All of these
23
Q
- Industrial paddle agitators turn at the speed of
A
- 20 and 150 rpm
24
Q
- The dynamic technique is based on the
A
- Oxygen material balance in an aerated batch fermenter during the growth of microorganisms
25
25. The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams
25. All of the above answers
26
26. During fermentation, the saturation concentration of oxygen was reduced from 7 ppm to 1 ppm. Which one of the following conclusions can be drawn?
26. Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration
27
27. If the stirrer speed is too slow, bubbles will accumulate and coalesces under the impeller. This phenomenon is known as a
27. Flooded impeller
28
28. 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?
28. The growth rate is limited by the rate of mass transfer of the alkane into the fermentation medium
29
29. Reynolds (Reii) number for the impeller is given by (where Dii), stirrer diameter; N, stirrer speed; p, density of fluid; and μ, viscosity of fluid).
29. Di2Nρ/μDi2Nρ/μ
30
30. The advantage of axial flow impellers over radial flow impellers is that axial flow impellers
30. Provide low shear conditions
31
31 Larger propellers turn at the speed of
31. 400 to 800 rpm
32
32. A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen
32. Concentration is less than the critical concentration
33
33. Which of the following model holds correct for the two-film theory? (where KLL is the mass transfer coefficient, DABDAB diffusivity and ZfZf film thickness)
33. KL=DAB/ZfKL=DAB/Zf
34
34. Froude number is avoided in calculation of power requirements for low viscosity liquid mixing systems when
34. Baffled systems are used
35
35. A fermentation system has a K11a of 3 s−1−1 and a C0+0+ of 5 ppm of O22. If the bulk liquid is completely depleted of oxygen, then the oxygen transfer rate will be equal to
35. 15 mg L-1 s-1
36
36. During aeration, a cylindrical reactor had a height of 10 m. Without aeration, the height was 7.5 m. Under these aeration and mixing conditions, the gas hold up in the reactor is
36. 25%
37
37. A fermentation system has a K11a of 3 s−1−1 and a Co++ of 5 ppm of O22. If the bulk liquid is saturated with oxygen, then the oxygen transfer rate will be equal to
37. Zero
38
38. Which of the following would be best described as radial flow impeller?
38. A Rushton turbine
39
39. Small propellers turn at the speed of either
39. 1150 rpm or 1750 rpm
40
40. In aerobic microorganisms cultures radial flow impellers are used because
40. They provide high shear mixing conditions
