Mass Transfer Set 16

Mechanical Engineering

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This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on Mass Transfer Set 16

Q1 | Pick out the wrong statement pertaining to leaching.
  • Fine solids cannot be leached in a Pachuca tank
  • Door classifier can be used for leaching of coarse solids
  • Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor
  • Very high temperature is not needed for the leaching of sugar beet
Answer: Fine solids cannot be leached in a Pachuca tank
Q2 | Azeotropism for ethyl alcohol-water system disappears by
  • Increasing temperature
  • Decreasing pressure
  • Increasing pressure
  • No means
Answer: Decreasing pressure
Q3 | Ordinary diffusion process is also called __________ diffusion.
  • Pressure
  • Thermal
  • Concentration
  • Forced
Answer: Concentration
Q4 | The falling rate period in the drying of a solid is characterised by
  • Increase in rate of drying
  • Increasing temperatures both on the surface and within the solid
  • Decreasing temperatures
  • None of these
Answer: Increasing temperatures both on the surface and within the solid
Q5 | Decoction refers to the use of solvent
  • At ambient temperature
  • At its boiling point
  • In its vapor form
  • None of these
Answer: At its boiling point
Q6 | Schmidt number and Lewis number for pure air at atmospheric conditions are respectively
  • < 1 and ? 1
  • 1 and 0
  • > 1 and ? 1
  • 0 and ? 1
Answer: < 1 and ? 1
Q7 | Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.
  • Wetted wall
  • Bubble cap
  • Perforated tray
  • Packed
Answer: Wetted wall
Q8 | Pick out the correct statement.
  • For identical gas flow rates, less pressure drop occurs through a plate tower than through a packed tower
  • 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
  • For the same duty, plate columns weigh less than packed columns
  • All (A), (B) and (C)
Answer: All (A), (B) and (C)
Q9 | The solvent used in liquid-liquid extraction should have __________ less than one.
  • Selectivity
  • Distribution co-efficient
  • Both (A) and (B)
  • Neither (A) nor (B)
Answer: Neither (A) nor (B)
Q10 | 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
  • Mass transfer co-efficient
  • Thermal diffusivity
  • Kinematic viscosity
  • Volumetric diffusivity
Answer: Mass transfer co-efficient
Q11 | Pick out the wrong statement.
  • Different solids have different equilibrium moisture curves
  • Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column
  • Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column
  • Even a forced draft cooling tower cannot cool water below the wet bulb temperature
Answer: Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column
Q12 | Which of the following equipments is not used for liquid dispersion?
  • Wetted wall towers
  • Packed towers
  • Venturi scrubbers
  • Agitated vessels
Answer: Agitated vessels
Q13 | The rough value of diffusion co-efficient of water vapor into air at 25°C may be about __________ cm2/sec.
  • 0.25
  • 2.5
  • 1.25
  • 0.0025
Answer: 0.25
Q14 | Molecular diffusion is caused by the
  • Transfer of molecules from low concentration to high concentration region
  • Thermal energy of the molecules
  • Activation energy of the molecules
  • Potential energy of the molecules
Answer: Thermal energy of the molecules
Q15 | Liquid diffusivity is of the order of __________ cm2 /second.
  • 0.01
  • 0.1
  • 10-5 to 10-6
  • > 1
Answer: 10-5 to 10-6
Q16 | The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (forcomponent B diffusing in A) for a binary mixture of
  • Newtonian liquids
  • Non-Newtonian liquids
  • Ideal gases
  • Real gases
Answer: Ideal gases
Q17 | Can a cooling tower cool water below the wet bulb temperature of inlet air?
  • Yes
  • No
  • Yes; but height of cooling tower will be prohibitively high
  • Yes; but the air flow rate should be excessively high
Answer: No
Q18 | The expression, ln(F/W) = ? xF xW [dx/y* - x)] is
  • Differential distillation equation
  • For NtoG in absorption for dilute mixture
  • Slope of q-line in McCabe-Thiele method
  • For relative volatility
Answer: Differential distillation equation
Q19 | Wetted wall tower experiment determines the
  • Molal diffusivity
  • Volumetric co-efficient
  • Mass transfer co-efficient
  • None of these
Answer: Mass transfer co-efficient
Q20 | Condensation of a vapour-gas mixture just begins, when (where, p = partial pressure of the vapour P = vapour pressure of the liquid).
  • p = P
  • p >>P
  • p < P
  • p << P
Answer: p = P
Q21 | If the overall efficiency and Murphree plate efficiency are equal, then both the equilibrium and operating lines are:
  • Straight
  • Parallel
  • Both (A) & (B)
  • Neither (A) nor (B)
Answer: Both (A) & (B)
Q22 | JD factor for mass transfer is a function of Reynolds number. Mass transfer by molecular diffusion from a single drop to surrounding still air is given by
  • Nsh = 2
  • Nst = 2
  • Nsc = 2
  • None of these
Answer: Nsh = 2
Q23 | In liquid-liquid extraction, the number of phases at plait point is
  • 1
  • 2
  • 3
  • 4
Answer: 1
Q24 | Molecular sieves are porous
  • Alumina
  • Silica
  • Synthetic zeolites crystals/metal alumino-silicates
  • None of these
Answer: Synthetic zeolites crystals/metal alumino-silicates
Q25 | Nitrobenzene (boiling point = 210.6°C) is steam distilled at 1 atm pressure. Nitrobenzene will distil off __________ °C.
  • At < 100
  • At > 210.6
  • Between 100 and 210
  • None of these
Answer: At < 100
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