Agitation and Aeration – Section 2

6. Pure oxygen, if used instead of air will increase oxygen transfer rates because

A. the saturation concentration of oxygen is higher
B. the bubble size is smaller
C. the oxygen transfer coefficient is larger
D. the partial pressure of oxygen in the gas phase is lower

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7. For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (k_L) co-relating power consumption (P_m) and fermenter volume (V) can be expressed as

A. k_L ∝ (P_m/V)^0.33
B. k_L ∝ (P_m/V)^0.66
C. k_L ∝ (P_m/V)^0.50
D. k_L ∝ (P_m/V)

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8. Higher temperatures affect oxygen transfer rates by

A. increasing K_La but lowering C*_o
B. lowering K_La but increasing C*_o
C. increasing K_La and increasing C_o
D. lowering K_La and lowering C_o

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9. The Intermig impeller is

A. an axial flow impeller which can be used for the culture of aerobic organisms
B. directed upwards rather than towards the base of the reactor
C. a fork-shaped extensions to the impeller facilitate bubble break up
D. All of the above

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10. Main reason for using baffles in stirred tank reactors are

A. baffles permit turbulence conditions to arise at low stirrer speed
B. baffles will allow axial mixing to occur even with radial flow impellers
C. both (a) and (b)
D. baffles prevent turbulent conditions in stirred tank reactors

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