Biochem - Agitation and Aeration (S3)

Question 1

1. The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that

Answer 1

1. As the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form

Question 2

2. Turbulent flow range of mixing speed is obtained for

Answer 2

2. Rei>104Rei​>104

Question 3

3. For laminar flow, Reynolds number is correlated with power number as (whereKK, a constant which depends on the container geometry and shape of stirrer;ReiRei​is Reynolds number for agitator;DiDi​, stirrer diameter; andNN, stirrer speed).

Answer 3

3. Np=K(Rei)−1Np​=K(Rei​)−1

Question 4

4. For turbulent flow, Reynolds number is correlated with power number as (whereKK, a constant which depends on the container geometry and shape of stirrer;ReiRei​is Reynolds number for agitator;DiDi​, stirrer diameter; andNN, stirrer speed).

Answer 4

4. Np=KNp​=K

Question 5

5. In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg h−1−1, then the oxygen uptake will be

Answer 5

5. 23 kg h-1

Question 6

6. Axial flow impellers

Answer 6

6. Provide low shear conditions and are suited for use in shear sensitive processes

Question 7

7. Bioreactors, where vortex is formed, another dimensionless number, ___ is useful.

Answer 7

7. Froude

Question 8

8. Oxygen transfer rate is increased with an increase in the stirrer speed in aerated bioreactor because

Answer 8

8. All of the above

Question 9

9. 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

Answer 9

9. The reaction was mass transfer limited at 300 rpm

Question 10

10. An increase in the heat transfer in the stirred tank reactor will be observed at

Answer 10

10. Higher stirrer speed

Question 11

11. In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where Vs and Vii​are the superficial gas velocity and bubble rise velocity).

Answer 11

11. H=Vs/(Vs+Vi)H=Vs/(Vs+Vi​)

Question 12

12. What is the effect of the concentration of dissolved salts and sugars on the oxygen transfer rate?

Answer 12

12. The saturation concentration of oxygen in the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate

Question 13

13. Which of the following impellers generate a flow parallel to the axis of shaft?

Answer 13

13. Axial flow

Question 14

14. In a tall reactor, oxygen transfer rates will be

Answer 14

14. Highest at the base of the reactor

Question 15

15. Which of the following impeller is used in situations where strong vertical currents are desirable for heavily suspending particles?

Answer 15

15. Propeller

Question 16

16. Laminar flow range of mixing speed is obtained for

Answer 16

16. Rei<10Rei​<10

Question 17

17. Which of the following number is calculated from the diameter and peripheral speed of the impeller?

Answer 17

17. Froude number

Question 18

18. A higher liquid height will lead to a higher gas hold up by which the oxygen transfer rate will be

Answer 18

18. Higher at the base of the reactor

Question 19

19. The main function of the dimples provided in the cooling jacket is to

Answer 19

19. Increase the level of turbulence of the cooling water in the jacket

Question 20

20. The power required by an agitator operating in a gas-sparged system is

Answer 20

20. Lesser than the power required by an impeller in operating at same speed in a gas free system

Question 21

21. Which of the following will have the largest interfacial area per unit volume?

Answer 21

21. A bubble with a diameter of 1 mm

Question 22

22. Which device is commonly used for measuring the rate of rotation (rpm) of the stirrer shaft?

Answer 22

22. Tachometer