11. 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)

A. H = V_s/(V_s–V_t)
B. H = V_s/(V_s+ V_t)
C. H = V_s/(V_s.V_t)
D. H = (V_s+V_t)/V_s

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

A.The saturation concentration of oxygen in the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
B.The K_La of the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
C.The K_La of the medium increases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
D. None of the above

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

A. Axial flow
B. Radial flow
C. Both (a)and(b)
D. None of these

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

A. highest at the surface of the reactor
B. highest at the base of the reactor
C. highest in the middle of the reactor
D. the same throughout the reactor

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

A. Propeller
B. Paddle
C. Turbine
D. None of these