Mass Transfer - Chemical Engineering Questions and Answers - Set 27

Practice Test: Question Set - 27

1. Ordinary diffusion process is also called __________ diffusion.
    (A) Pressure
    (B) Thermal
    (C) Concentration
    (D) Forced
2. The falling rate period in the drying of a solid is characterized by
    (A) Increase in rate of drying
    (B) Increasing temperatures both on the surface and within the solid
    (C) Decreasing temperatures
    (D) None of these
3. Decoction refers to the use of solvent
    (A) At ambient temperature
    (B) At its boiling point
    (C) In its vapor form
    (D) None of these
4. Schmidt number and Lewis number for pure air at atmospheric conditions are respectively
    (A) < 1 and ≈ 1
    (B) 1 and 0
    (C) > 1 and ≈ 1
    (D) 0 and ≈ 1
5. Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.
    (A) Wetted wall
    (B) Bubble cap
    (C) Perforated tray
    (D) Packed
6. Pick out the correct statement.
    (A) For identical gas flow rates, less pressure drop occurs through a plate tower than through a packed tower
    (B) Plate column can handle greater liquid loads without flooding than packed column, but the liquid hold up is more in the case of plate column
    (C) For the same duty, plate columns weigh less than packed columns
    (D) All (a), (b) and (c)
7. The solvent used in liquid-liquid extraction should have __________ less than one.
    (A) Selectivity
    (B) Distribution co-efficient
    (C) Both (a) and (b)
    (D) Neither (a) nor (b)
8. Diffusion co-efficient generally depends upon the temperature, pressure & the nature of the components of the system. Its dimension is not the same as that of the
    (A) Mass transfer co-efficient
    (B) Thermal diffusivity
    (C) Kinematic viscosity
    (D) Volumetric diffusivity
9. Pick out the wrong statement.
    (A) Different solids have different equilibrium moisture curves
    (B) Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column
    (C) Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column
    (D) Even a forced draft cooling tower cannot cool water below the wet bulb temperature
10. Which of the following equipments is not used for liquid dispersion?
    (A) Wetted wall towers
    (B) Packed towers
    (C) Venturi scrubbers
    (D) Agitated vessels
11. The rough value of diffusion co-efficient of water vapor into air at 25°C may be about __________ cm2/sec.
    (A) 0.25
    (B) 2.5
    (C) 1.25
    (D) 0.0025
12. Molecular diffusion is caused by the
    (A) Transfer of molecules from low concentration to high concentration region
    (B) Thermal energy of the molecules
    (C) Activation energy of the molecules
    (D) Potential energy of the molecules
13. Liquid diffusivity is of the order of __________ cm2 /second.
    (A) 0.01
    (B) 0.1
    (C) 10-5 to 10-6
    (D) > 1
14. The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (for component B diffusing in A) for a binary mixture of
    (A) Newtonian liquids
    (B) Non-Newtonian liquids
    (C) Ideal gases
    (D) Real gases
15. Can a cooling tower cool water below the wet bulb temperature of inlet air?
    (A) Yes
    (B) No
    (C) Yes; but height of cooling tower will be prohibitively high
    (D) Yes; but the air flow rate should be excessively high
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