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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • Which of the following would be best described as an axial flow impeller?


  • Options
  • A. An impeller with blades pitched at 45° to the vertical
  • B. An impeller which directs liquid flow towards the base of the reactor
  • C. Both (a) and (b)
  • D. An impeller with blades pitched at 75° to the vertical

  • Correct Answer
  • Both (a) and (b) 


  • Agitation and Aeration problems


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    • 1. Surface renewal theory predicts that the mass transfer coefficient is

    • Options
    • A. directly proportional to the square root of the molecular diffusivity
    • B. inversely proportional to the square root of the molecular diffusivity
    • C. directly proportional to the cube root of the molecular diffusivity
    • D. indirectly proportional to the cube root of the molecular diffusivity
    • Discuss
    • 2. Penetration theory assumes that turbulent eddies travel from the bulk of the phase to the interface where they remain constant for a constant exposure time (te). The model correlating KL, mass transfer coefficient and DAB, diffusivity can be expressed as

    • Options
    • A. KL = 2(DAB/?te)0.25
    • B. KL = 2(DAB/?te)0.5
    • C. KL = 2(DAB/?te)0.75
    • D. KL = 2(DAB/?te)
    • Discuss
    • 3. Which have the maximum resistance while transferring carbon dioxide from the bulk liquid to an air bubble?

    • Options
    • A. Moving through the gas liquid interface
    • B. Moving through the bubble boundary layer
    • C. Moving across the cell membrane
    • D. Moving through the bulk liquid
    • Discuss
    • 4. The lowest yield of ATP /is in

    • Options
    • A. fermentation
    • B. aerobic respiration
    • C. anaerobic respiration
    • D. same in (a), (b) and (c)
    • Discuss
    • 5. The growth of an organism on glucose is described by the following Monod model parameters: ?m = 0.5 h-1 and Ks =0.1 g.l-1, if the concentration of glucose in the feed is 10 g.l-1 and the dilution rate is set to 0.4 h-1, then the steady state concentration of glucose in the effluent will be

    • Options
    • A. 0 g.l-1
    • B. 0.5 g.l-1
    • C. 1.0 g.l-1
    • D. 10 g.l-1
    • Discuss
    • 6. Which of the following type(s) of stirrer can be used for microbiological processes?

    • Options
    • A. Mig
    • B. Intermig
    • C. Turbine
    • D. All of these
    • Discuss
    • 7. Which of the following is most likely to cause an increase in the rate of oxygen transfer into a particular aerated fermentation system?

    • Options
    • A. Addition of antifoams
    • B. Increase in temperature
    • C. Increase in stirrer speed
    • D. Both (a) and (b)
    • Discuss
    • 8. Which of the following will have the highest surface area available for oxygen transfer?

    • Options
    • A. A shake flask
    • B. A standing test tube
    • C. A non-sparged stirred tank reactor agitated at 400 rpm
    • D. A sparged stirred tank reactor agitated at 400 rpm
    • Discuss
    • 9. 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

    • Options
    • A. 0.793atml/mmol
    • B. 0.207atml/mmol
    • C. 1.26 atml/mmol
    • D. 8.74 atml/mmol
    • Discuss
    • 10. The oxygen transfer rate in a bioreactor will increase if

    • Options
    • A. oil is added
    • B. antifoam is added
    • C. detergent like molecules are added
    • D. increase in the reactor temperature
    • Discuss


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