# Separation Processes Questions and Answers – Mass Transfer in Laminar Flow

This set of Separation Processes Multiple Choice Questions & Answers (MCQs) focuses on “Mass Transfer in Laminar Flow”.

1. 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

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

2. 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

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

3. What value of Reynold’s number is obtained with water?
a) 8
b) 16
c) 25
d) 50

Explanation: The value of 25 is obtained with water.

4. What value of reynold’s number represents a laminar flow?
a) 3
b) 2500
c) 5000
d) 78

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

5. 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

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

6. 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

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

7. 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

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

8. 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

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

9. What is the correct formula for nusselt’s number?
a) hµ/k
b) hρ/k
c) hL/k
d) hΔTL/k

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

10. 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

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

Sanfoundry Global Education & Learning Series – Separation Processes.

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