QuizMaster

Question: The power required by an impeller in a gas sparged system compare to the power required by impeller operating at same speed in a gas free liquid is usually
[A].

lesser

[B].

higher

[C].

same

[D].

may be lesser or higher depending upon the geometry

Answer: Option A

Explanation:

No answer description available for this question.

Question: 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

Answer: Option B

Explanation:

No answer description available for this question.

Question: The average fractional gas hold up (H) can be given as (where Zf and Zl are the level of aerated and clear liquid respectively)
[A].

H = (Zf-Zl)/Zf

[B].

H = Zf/Zl

[C].

H = Zf/ZfZl

[D].

H =(Zf+Zl)/Zf

Answer: Option A

Explanation:

No answer description available for this question.

Question: Gas hold up, characterizing the hydrodynamics in a fermenter, mainly depends on the
[A].

superficial gas velocity

[B].

power consumption

[C].

Both (a) and (b)

[D].

gas concentration

Answer: Option C

Explanation:

No answer description available for this question.

Question: Surface renewal theory predicts that the mass transfer coefficient is
[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

Answer: Option A

Explanation:

No answer description available for this question.

Question: 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
[A].

KL = 2(DAB/πte)0.25

[B].

KL = 2(DAB/πte)0.5

[C].

KL = 2(DAB/πte)0.75

[D].

KL = 2(DAB/πte)

Answer: Option B

Explanation:

No answer description available for this question.

Question: Which of the following model holds correct for the two-film theory? (where KL is the mass transfer coefficient, DAB diffusivity and Zf film thickness)
[A].

KL = DAB/Zf

[B].

KL = DAB

[C].

KL= Zf/DAB

[D].

KL = DAB.Zf

Answer: Option A

Explanation:

No answer description available for this question.

Question: Which of the following is not considered among the three best-known theories of interphase mass transfer?
[A].

two-film theory

[B].

penetration theory

[C].

surface renewal theory

[D].

Calderbank and Moo-Young theory

Answer: Option D

Explanation:

No answer description available for this question.

Question: 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

Answer: Option C

Explanation:

No answer description available for this question.

Question: The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that
[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

Answer: Option C

Explanation:

No answer description available for this question.