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# Separation Processes MCQ’s – Steady and Unsteady State Mass Transfer Through Stationary Media

1 - Question

The molar diffusion flux for a cylinder with inner radius r1 and outer radius r2 is directly proportional to:

a) Ln(r2/r1)

b) R2/r1

c) 1/ln(r1/r2)

d) 1/ln(r2/r1)

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Answer: dExplanation: The molar diffusion flux for a cylinder with inner radius r1 and outer radius r2 is 2LDab(ca1-ca2)/ ln(r2/r1).

2 - Question

The molar diffusion flux for a plane wall with thickness z2-z1 is directly proportional to:

a) Z2

b) Z2-z1

c) 1/z2-z1

d) Z1-z2

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Answer: cExplanation: The molar diffusion flux for a plane wall with thickness z2-z1 is Dab(ca1-ca2)/ z2-z1.

3 - Question

The molar diffusion flux for a spherical shell with inner radius r1 and outer radius r2 is directly proportional to

a) 4r1r2/r2-r1

b) r2-r1/4r1r2

c) r1r2/r2-r1

d) 2r1r2/r2-r1

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Answer: aExplanation: The molar diffusion flux for a spherical shell with inner radius r1 and outer radius r2 is 4r1r2 Dab(ca1-ca2)/r2-r1.

4 - Question

For which mass transfer the area log mean is considered?

a) Through a sphere

b) Through a cylinder

c) Through a wall

d) Through a ball

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Answer: bExplanation: The mass transfer through a cylinder is given by the formula 2Lab(ca1-ca2)/ ln(r2/r1).Hence log mean of the area is considered.

5 - Question

For which mass transfer the area geometric mean is considered?

a) Through a sphere

b) Through a cylinder

c) Through a wall

d) Through a pipe

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Answer: aExplanation: The molar diffusion flux for a spherical shell with inner radius r1 and outer radius r2 is 4r1r2 Dab(ca1-ca2)/r2-r1.Hence the geometric mean area is considered.

6 - Question

The molar diffusion rate of A in stationary B in only z direction is given by:

a) DabA(ΔCa/Δz)

b) DabA(Δz)

c) -DabA(ΔCa/Δz)

d) DabA(ΔCa)

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Answer: cExplanation: The molar diffusion rate of A in stationary B in only z direction is given by -DabA(ΔCa/Δz).

7 - Question

For one dimensional diffusion in the radial direction only for cylinder and sphere, the fick’s second law becomes:

a) ΔCa/ΔT= Dab/r(Δ/Δr(rΔCa/Δr)

b) ΔCa/ΔT= Dab/(Δ/Δr(ΔCa/Δr)

c) -ΔCa/ΔT= Dab/r(Δ/Δr(rΔCa/Δr)

d) ΔCa/ΔT= Dab/r(Δ/Δr(r/Δr)

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Answer: aExplanation: For one dimensional diffusion in the radial direction only for cylinder and sphere, the fick’s law becomes ΔCa/ΔT= Dab/r(Δ/Δr(rΔCa/Δr).

8 - Question

The fick’s second law is analogous to:

a) Newton;s second law

b) Newton’s third law

c) Fourier’s second law

d) Fourier’s first law

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Answer: cExplanation: The fick’s second law is analogous to fourier’s second law where ca is replaced by temperature T and and Dab by thermal diffusivity.

9 - Question

Which equation is concerned with adsorption equilibria.

a) Gibb’s equation

b) Fourier’s law

c) Fick’s law

d) Freundlich’s equation

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Answer: dExplanation: the freunlich’s equation of x/m = Kp1/n is concerned with adsorption equilibria

10 - Question

For a wetted watch tower, what is the area of mass transfer?

a) Rectangular

b) Spherical

c) Cylindrical

d) Hexagonal

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Answer: cExplanation: The shape of a watch tower is cylindrical, hence the area must be cylindrical.