MCQ on Diffusion Mass Transfer - Set 14 - ObjectiveBooks
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# Practice Test: Question Set - 14

1. All moisture in a non-hygroscopic material is the __________ moisture.
(A) Free
(B) Equilibrium
(C) Unbound
(D) Bound

2. Molecular diffusivity of a liquid
(A) Increases with temperature
(B) Decreases with temperature
(C) May increase or decrease with temperature
(D) Is independent of temperature

3. Raschig ring made of porcelain cannot be used for treating concentrated
(A) Hydrochloric acid
(B) Nitric acid
(C) Alkalis
(D) Sulphuric acid

4. Use of natural draft cooling tower is practiced, when the air has low
(A) Humidity
(B) Temperature
(C) Both 'a' & 'b'
(D) Neither 'a' nor 'b'

5. At a fixed pressure, the humidity depends upon the partial pressure of vapor in the mixture. Humidity of a vapor free gas is __________ percent.
(A) 100
(B) 0
(C) 50
(D) Between 0 and 100

6. Tower diameter may be decreased by
(A) Using higher reflux ratio
(B) Use of increased tray spacing
(C) Increasing the liquid flow rate
(D) Increasing the vapor flow rate

7. Pick out the wrong statement.
(A) The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are the same for NSc = NPr= 1
(B) 1 Nm3 of dry air is lighter than 1Nm3 of humid air
(C) The Lewis number of a mixture is unity, when the thermal diffusivity is equal to the mass diffusivity
(D) An Azeotropic mixture of two liquids has boiling point higher than either of them, when it shows negative deviation from Raoult's Law

8. The humid volume may be increased by increasing the
(A) Temperature at constant humidity
(B) Humidity at constant temperature
(C) Both (a) and (b)
(D) Neither (a) nor (b)

9. Pick out the correct relationship. (Where, Ri = internal reflux ratio Ro = external reflux ratio.)
(A) (1 + Ro) = Ro/Ri
(B) (1 - Ro) = Ro/Ri
(C) (1 + Ri) = Ro/Ri
(D) (1 - Ri) = Ro/Ri

10. According to Poiseuille's law, the permeability for gas flow through a capillary is proportional to (where, μ = gas viscosity)
(A) μ
(B) 1/μ
(C) √μ
(D) μ2

11. Even though bubble cap towers are very effective for humidification operation, they are not used commonly in industries, because of the
(A) High evaporation losses of water
(B) High pressure drop of the gas
(C) Difficulty in its fabrication
(D) None of these

12. In case of constant underflow extraction operation, the __________ at all solute concentration.
(A) Solids are drained to the same extent
(B) Ratio of the insoluble to solution is constant
(C) Both (a) & (b)
(D) Neither (a) nor (b)

13. Which of the following has the same dimension as mass diffusivity?
(A) Momentum flux
(B) Kinematic viscosity
(C) Thermal diffusivity
(D) Both (b) and (c)

14. Packed column distillation is limited to the column __________ meters.
(A) Height < 6
(B) Diameter < 0.6
(C) Both (a) & (b)
(D) Neither (a) nor (b)

15. Which of the following decreases during evaporative cooling process with recirculated water supply?
(A) Wet bulb temperature
(B) Relative humidity
(C) Partial pressure of vapor
(D) None of these

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