# Separation Processes Questions and Answers – Steady and Unsteady State Mass Transfer Through Stationary Media

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This set of Separation Processes Questions and Answers for Experienced people focuses on “Steady and Unsteady State Mass Transfer Through Stationary Media”.

1. 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)

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

2. 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

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

3. 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

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

Explanation: 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. 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

Explanation: 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. 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)

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

7. 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)

Explanation: 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. 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

Explanation: 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. Which equation is concerned with adsorption equilibria.
a) Gibb’s equation
b) Fourier’s law
c) Fick’s law
d) Freundlich’s equation

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

10. For a wetted watch tower, what is the area of mass transfer?
a) Rectangular
b) Spherical
c) Cylindrical
d) Hexagonal

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

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