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Home Biochemical Engineering Agitation and Aeration Comments

  • Question
  • Oxygen transfer rate is increased with an increase in the stirrer speed in aerated bioreactor because


  • Options
  • A. it decrease the bubble size
  • B. it decreases the size of the boundary layer surrounding a bubble
  • C. it increases the rate of movement of oxygen molecules through the bulk liquid
  • D. all of the above

  • Correct Answer
  • all of the above 


  • Agitation and Aeration problems


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    • 1. In a tall reactor, oxygen transfer rates will be

    • Options
    • 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
    • Discuss
    • 2. A higher liquid height will lead to a higher gas hold up by which the oxygen transfer rate will be

    • Options
    • A. higher throughout the reactor
    • B. lower throughout the reactor
    • C. higher at the base of the reactor
    • D. lower at the base of the reactor
    • Discuss
    • 3. The main function of the dimples provided in the cooling jacket is to

    • Options
    • A. increase the level of turbulence of the cooling water in the jacket
    • B. increase the residence time of the cooling water in the jacket
    • C. increase the cooling water-jacket wall boundary layer size
    • D. all of the above
    • Discuss
    • 4. Which of the following number is calculated from the diameter and peripheral speed of the impeller?

    • Options
    • A. Reynolds number
    • B. Froude number
    • C. Power number
    • D. None of these
    • Discuss
    • 5. Which of the following impeller is used in situation where strong vertical currents are desirable for suspending heavily particles?

    • Options
    • A. Propeller
    • B. Paddle
    • C. Turbine
    • D. None of these
    • Discuss
    • 6. An increase in the heat transfer in the stirred tank reactor will be observed at

    • Options
    • A. higher cooling water temperature
    • B. higher stirrer speed
    • C. the removal of baffles from the reactor
    • D. slower stirrer speed
    • Discuss
    • 7. For laminar 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(Rei)
    • D. Np = KNDi(Rei)-2
    • Discuss
    • 8. Which of the following impellers generate a flow parallel to the axis of shaft?

    • Options
    • A. Axial flow
    • B. Radial flow
    • C. Both (a)and(b)
    • D. None of these
    • Discuss
    • 9. What is the effect of the concentration of dissolved salts and sugars on the oxygen transfer rate?

    • Options
    • 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 KLa of the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
    • C. The KLa of the medium increases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate
    • D. None of the above
    • Discuss
    • 10. The power required by an agitator operating in a gas-sparged system is

    • Options
    • A. lesser than the power required by an impeller in operating at same speed in a gas free system
    • B. more than the power required by an impeller in operating at same speed in a gas free system
    • C. same as the power required by an impeller in operating at same speed in a gas free system
    • D. none of the above
    • Discuss


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