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Biochemical Engineering Objective Questions { Agitation and Aeration }

85. In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h-1, then the oxygen uptake will be
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
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86. Axial flow impellers
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
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87. Bioreactors, where vortex is formed, another dimensionless number, __________ is useful.
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88. xygen transfer rate is increased with an increase in the stirrer speed in aerated bioreactor because
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
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89. 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
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
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90. An increase in the heat transfer in the stirred tank reactor will be observed at
A.higher cooling water temperature
B.higher stirrer speed
C.the removal of baffles from the reactor
D.slower stirrer speed
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91.  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)
A.H = Vs/(Vs-Vt)
B.H = Vs/(Vs+ Vt)
C.H = Vs/(Vs.Vt)
D.H = (Vs+Vt)/Vs
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