Agitation and Aeration problems
- 1. In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h-1, then the oxygen uptake will be
Options- A. 23 kg.h-1
- B. less than 23 kg.h-1
- C. greater than 23 kg.h-1
- D. 2.3 kg.h-1 Discuss
Correct Answer: 23 kg.h-1
- 2. In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where Vs and Vt are the superficial gas velocity and bubble rise velocity)
Options- A. H = Vs/(Vs-Vt)
- B. H = Vs/(Vs+ Vt)
- C. H = Vs/(Vs.Vt)
- D. H = (Vs+Vt)/Vs Discuss
Correct Answer: H = Vs/(Vs+ Vt)
- 3. For turbulent flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Rei, is Reynolds number for agitator; Di, stirrer diameter and N, stirrer speed)
Options- A. Np = K(Rei)-1
- B. Np = N2Di(Rei)-1
- C. Np = K
- D. Can't be correlated Discuss
Correct Answer: Np = K
- 4. Which of the following will have the largest interfacial area per unit volume?
Options- A. A bubble with a diameter of 1 mm
- B. A bubble with a diameter of 5 mm
- C. A bubble with a diameter of 15 mm
- D. A bubble with a diameter of 50 mm Discuss
Correct Answer: A bubble with a diameter of 1 mm
- 5. The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that
Options- A. a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime
- B. as the stirrer speed increases, the liquid will continue to circulate and then become turbulent
- C. as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
- D. A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate Discuss
Correct Answer: as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form.
- 6. Bioreactors, where vortex is formed, another dimensionless number, __________ is useful.
Options- A. Stanton
- B. Rayleigh
- C. Bond
- D. Froude Discuss
Correct Answer: Froude
- 7. Turbulent flow range of mixing speed is obtained for
Options- A. Rei<10
- B. 10<Rei<104
- C. Rei>104
- D. None of these Discuss
Correct Answer: Rei>104
- 8. Which device is commonly used for measuring the rate of rotation (rpm) of the stirrer shaft?
Options- A. Anemometer
- B. Manometer
- C. Tachometer
- D. Barometer Discuss
Correct Answer: Tachometer
- 9. Axial flow impellers
Options- A. provide high shear conditions for breaking up bubbles
- B. provide low shear conditions and are suited for use in shear sensitive procesess
- C. provide direct flow towards the walls of the reactor
- D. none of the above Discuss
Correct Answer: provide low shear conditions and are suited for use in shear sensitive procesess
- 10. 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
Options- A. the reaction was mass transfer limited at 300 rpm
- B. the reaction was mass transfer limited at 500 rpm
- C. the reaction did not involve any mass transfer step
- D. the movement of molecules in the reactor at 300 rpm occurred due to diffusion alone Discuss
Correct Answer: the reaction was mass transfer limited at 300 rpm
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