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This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on Mass Transfer Set 1

Q1 | According to the Fenske equation, what will be the minimum number of plates required in a distillation column to separate an equimolar binary mixture of components A and B into an overhead fraction containing 99 mol% A and a bottom fraction containing 98 mol% B ? Assume that relative volatility (?AB = 2) does not change appreciably in the column.
  • 5
  • 9
  • 12
  • 28
Q2 | With increase in the mass velocity of the gas, the rate of drying during the constant rate period __________, if the conduction and radiation through the solid are negligible.
  • Increases
  • Decreases
  • Remain same
  • Increases linearly
Q3 | During the constant rate period of drying of a solid,
  • Increased air humidity decreases the rate of drying
  • Increasing the air temperature decreases the drying rate
  • Surface evaporation of unbound moisture occurs
  • None of these
Q4 | Large scale drying of wheat is done in a __________ dryer.
  • Fluidised bed
  • Spouted bed
  • Tray
  • Vacuum rotary
Q5 | Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is
  • Insoluble in the liquid
  • Soluble in the liquid
  • Non-ideal in nature
  • At a fixed temperature
Q6 | With increase in temperature, the leaching rate increases due to
  • Decreased liquid viscosity
  • Increased diffusivity
  • Both (A) and (B)
  • Neither (A) nor (B)
Q7 | As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages
  • Increase
  • Decrease
  • Remain unchanged
  • Can either increase or decrease, depends on the system
Q8 | In distillation where q is defined as the moles of liquid flow in the stripping section per mole of feed introduced, for saturated liquid feed
  • q > 1
  • q < 1
  • q = 1
  • q = 0
Q9 | Large scale drying of sugar is done in a __________ dryer.
  • Spouted bed
  • Tray
  • Rotary
  • Truck
Q10 | Though, theoretically the adsorption & desorption isotherms is expected to coincide but sometimes at least a part of the isotherms does not coincide and this phenomenon is known as adsorption hysteresis. In such cases, the desorption equilibrium pressure is __________ that obtained for adsorption.
  • Lower than
  • Higher than
  • Same as
  • Either same or higher than
Q11 | H2S is being absorbed in a gas absorber unit. The height of the transfer unit based on the overall mass transfer coefficient on the gas side is 0.4 m. The equilibrium data is given by, y = 1.5 x. The bulk concentration of H2S has to be reduced from 0.05 to 0.001 mole fraction in the gas side. The height of the tower (in metres) corresponding to an operating line given by, y = 5x + 0.001 is
  • 2
  • 1.56
  • 1
  • 0.56
Q12 | Reboiler is considered as one theoretical plate, because
  • Of the assumption that vapour and liquid leaving the reboiler are in equilibrium
  • Vapour is recycled to the column
  • Reboiler itself contains one plate
  • None of these
Q13 | In an absorption column, the flooding velocity for random packing is __________ that for stacked/regular packing.
  • Greater than
  • Smaller than
  • Equal to
  • Either (A), or (B); depends on the type of packing
Q14 | Experiments were conducted to determine the flux of a species A in a stagnant medium across a gas-liquid interface. The overall mass transfer co-efficient based on the liquid side for dilute systems for the above was estimated to be 4 × 10-3 kg mole/m2 .s. The equilibrium data for the system is given as y = 2x. The flux across the interface (in kg mole/m2 .s) for bulk concentrations of A in gas phase and liquid phase as y = 0.4 and x = 0.01 respectively is:
  • 5.6 × 10-4
  • 8.5 × 10-4
  • 5.6 × 10-3
  • 8.5 × 10-3
Q15 | In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the __________ number.
  • Lewis
  • Grashoff
  • Sherwood
  • None of these
Q16 | When the gas to be dissolved in liquid is a/an __________ then normally co-current adsorber are used.
  • Mixture of two gases
  • Pure gas
  • Ideal gas
  • Sparingly soluble gas
Q17 | Unsaturated air (with dry and wet bulb temperatures being 35 and 25°C respectively) is passed through water spray chamber maintained at 35°C. The air will be
  • Cooled
  • Humidified
  • Both (A) & (B)
  • Dehumidified
Q18 | __________ equation applies to diffusivities in liquids.
  • Gilliland
  • Hirschfelder
  • Wilke and Chang
  • None of these
Q19 | Mass transfer co-efficient is defined as
  • Flux = Co-efficient/concentration difference
  • Co-efficient = Flux/concentration difference
  • Flux=concentration difference/coefficient
  • None of these
Q20 | The relative volatility of a binary mixture at constant temperature __________ the total pressure.
  • Decreases with increase in
  • Increases with increase in
  • Is independent of
  • None of these
Q21 | Large quantity of silica gel is normally dried in a __________ dryer.
  • Freeze
  • Through circulation
  • Rotary vacuum
  • Tray
Q22 | The mass transfer co-efficient for a solid sphere of radius 'a' dissolving in a large volume ofquiescent liquid, in which „D’ is the diffusivity of solute, is
  • D/a
  • D/2a
  • Proportional to ?D
  • Dependent on the Reynolds number
Q23 | The value of „L/mG’ ratio for economical absorption operation ranges from
  • 0.5 to 0.8
  • 0.8 to 1.2
  • 1.25 to 2.0
  • 2.5 to 3.5
Q24 | Cox chart, which is useful in the design of distillation column particularly for petroleumhydrocarbons, is a plot of (where, P = vapor pressure, T = temperature).
  • log P vs. T
  • log P vs. log T
  • T vs. P
  • P vs. log T
Q25 | In a single stage extraction process, 10 kg of pure solvent S (containing no solute A) is mixed with 30 kg of feed F containing A at a mass fraction xf = 0.2. The mixture splits into an extract phase E and a raffinate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg)
  • 6.89
  • 8.89
  • 10
  • 8.25