21. The reason of using a flat disk in a Turbine is
A. to create high shear conditions
B. to break up bubbles more efficiently than the impeller blades
C. to ensure that the bulk of the energy consumption occurs at the blades
D. all of the above
22. Which of the following is not considered among the three best-known theories of interphase mass transfer?
A. two-film theory
B. penetration theory
C. surface renewal theory
D. Calderbank and Moo-Young theory
23. Which of the following is most likely to cause an increase in the rate of oxygen transfer into a particular aerated fermentation system?
A. Addition of antifoams
B. Increase in temperature
C. Increase in stirrer speed
D. Both (a) and (b)
24. 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. 0.793atml/mmol
B. 0.207atml/mmol
C. 1.26 atml/mmol
D. 8.74 atml/mmol
25. Gas hold up, characterizing the hydrodynamics in a fermenter, mainly depends on the
A. superficial gas velocity
B. power consumption
C. Both (a) and (b)
D. gas concentration