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# Separation Processes MCQ’s – Mass Transfer in Laminar Flow

1 - Question

The equation of motion for the liquid film in fully developed laminar flow in y-direction is:

a) µd2uy/dx2 + ρg =0

b) µd2uy/dy2 + ρg =0

c) µd2uy/dz2 + ρg =0

d) µd2uy/dx2 = 0

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Answer: cExplanation: Flow is in y direction but changes with respect to z-direction. Hence the equation of motion is µd2uy/dz2 + ρg =0.

2 - Question

Which two forces is the reynold’s number a ratio of?

a) Gravitational force and interfacial force

b) Interfacial force and viscous force

c) Thermal conductivity and electrical conductivity

d) Conduction and convection

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Answer: bExplanation: The reynold’s number Nre = 4τ/µ is the ratio of interfacial and viscous force.

3 - Question

What value of Reynold’s number is obtained with water?

a) 8

b) 16

c) 25

d) 50

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Answer: cExplanation: The value of 25 is obtained with water.

4 - Question

What value of reynold’s number represents a laminar flow?

a) 3

b) 2500

c) 5000

d) 78

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Answer: dExplanation: Only the value of 78 lies between 8 and 1200. SO it represents a laminar flow.

5 - Question

Which of the following is correct about Reynold’s number?

a) 3less thanNreless than1200

b) 3less thanreless than1600

c) 25less thanreless than1200

d) 8less thanreless than1200

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Answer: dExplanation: 8less thanreless than1200 are the correct boundary conditions for Reynold’s number.

6 - Question

Prandtl’s number is the ratio of which two quantities?

a) Momentum conductivity and thermal conductivity

b) Coefficient of convection to thermal conductivity

c) Momentum diffusivity and thermal diffusivity

d) Interfacial force and viscous force

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Answer: cExplanation: Prandtl’s number is the ratio of Momentum diffusivity and thermal diffusivity.

7 - Question

Which of the following is true about prandtl’s number?

a) Npr = Cpµ/k

b) Npr = Cpk/µ

c) Npr = Cvµ/k

d) Npr = Cpµ

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Answer: aExplanation: Prandtl’s number is the ratio of Momentum diffusivity and thermal diffusivity. Hence the formula is Npr = Cpµ/k.

8 - Question

What is the physical significance of nusselt’s number?

a) Ratio of convective heat transfer to conductive heat transfer

b) Ratio of convective heat transfer to conductive heat transfer

c) Ratio of total heat transfer to conductive heat transfer

d) Ratio of total transfer to convective heat transfer

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Answer: cExplanation: Nusselt number is the Ratio of convective heat transfer to conductive heat transfer.

9 - Question

What is the correct formula for nusselt’s number?

a) hµ/k

b) hρ/k

c) hL/k

d) hΔTL/k

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Answer: cExplanation: The nusselt number hL/k is the ratio of total heat transfer to onductive heat transfer.

10 - Question

Which of the following is most true?

a) Na = kcA(cai – ca)

b) Na = kcAΔc

c) Na = kcA(cai – ca)mean

d) Na = kcA(cai – ca)log mean

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Answer: bExplanation: Δc is taken as the driving force and is true every time. It’s expression will change depending upon the conditions