Biochem - Agitation and Aeration [S2] Flashcards
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
Q
- The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams
A
- All of the above answers
26
Q
- During fermentation, the saturation concentration of oxygen was reduced from 7 ppm to 1 ppm. Which one of the following conclusions can be drawn?
A
- Microbial growth is oxygen limited since the oxygen concentration is lesser than the saturation concentration
27
Q
- If the stirrer speed is too slow, bubbles will accumulate and coalesces under the impeller. This phenomenon is known as a
A
- Flooded impeller
28
Q
- 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?
A
- The growth rate is limited by the rate of mass transfer of the alkane into the fermentation medium
29
Q
- 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).
A
- Di2Nρ/μDi2Nρ/μ
30
Q
- The advantage of axial flow impellers over radial flow impellers is that axial flow impellers
A
- Provide low shear conditions
31
Q
31 Larger propellers turn at the speed of
A
- 400 to 800 rpm
32
Q
- A microbial population in a suspension culture will only be limited by oxygen availability if the dissolved oxygen
A
- Concentration is less than the critical concentration
33
Q
- Which of the following model holds correct for the two-film theory? (where KLLis the mass transfer coefficient,DABDABdiffusivity andZfZffilm thickness)
A
- KL=DAB/ZfKL=DAB/Zf
34
Q
- Froude number is avoided in calculation of power requirements for low viscosity liquid mixing systems when
A
- Baffled systems are used
35
Q
- A fermentation system has a K11a of 3 s−1−1and 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
A
- 15 mg L-1 s-1
36
Q
- 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
A
- 25%
37
Q
- A fermentation system has a K11a of 3 s−1−1and a Co++of 5 ppm of O22. If the bulk liquid is saturated with oxygen, then the oxygen transfer rate will be equal to
A
- Zero
38
Q
- Which of the following would be best described as radial flow impeller?
A
- A Rushton turbine
39
Q
- Small propellers turn at the speed of either
A
- 1150 rpm or 1750 rpm
40
Q
- In aerobic microorganisms cultures radial flow impellers are used because
A
- They provide high shear mixing conditions
