Free Mass Transfer Operations MCQs with Answers
669 Mass Transfer Operations MCQs from Chemical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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669 questions · page 16 of 34
- A. None of these
- B. Reduce the residence time of solid
- C. Increase the residence time of the solid
- D. Lift and shower the solids thus exposing it thoroughly to the drying action of the gas
Explanation: Flights pick up the solids and cascade them through the hot gas, repeatedly exposing fresh surfaces for heat and moisture transfer.
Correct answer: Lift and shower the solids thus exposing it thoroughly to the drying action of the gas- A. Both A. & B.
- B. Bulk flow
- C. Diffusion
- D. Neither A. nor B.
Explanation: Stefan's law treats diffusion through a stagnant component while also accounting for the bulk motion caused by unequal molar fluxes.
Correct answer: Both A. & B.- A. Mixture (to be separated) shows positive deviation from ideality
- B. Mixture (to be separated) shows negative deviation from ideality
- C. Relative volatility is reasonably constant
- D. Multi-component distillation is involved
Explanation: The Fenske relation estimates the minimum stages at total reflux using relative volatilities, commonly treating them as reasonably…
Correct answer: Relative volatility is reasonably constant- A. Increases pressure drop, increases surface area
- B. Increases pressure drop, decreases surface area
- C. Decreases pressure drop, decreases surface area
- D. Decreases pressure drop, increases surface area
Explanation: Raschig rings offer more effective contact area and generally a more open passage than irregular crushed stone.
Correct answer: Decreases pressure drop, increases surface area- A. Increasing the gas film co-efficient
- B. Increasing the liquid film co-efficient
- C. Increasing the total pressure
- D. Decreasing the total pressure
Explanation: Dilute NaOH reacts rapidly with absorbed SO2, making liquid-film resistance very small and leaving gas-film resistance dominant.
Correct answer: Increasing the gas film co-efficient- A. 0.01
- B. 10-5 to 10-6
- C. 0.1
- D. > 1
Explanation: Molecular diffusivity in liquids is much lower than in gases because liquid molecules are closely packed; its typical order is 10^-5 to…
Correct answer: 10-5 to 10-6- A. Transfer of molecules from low concentration to high concentration region
- B. Activation energy of the molecules
- C. Thermal energy of the molecules
- D. Potential energy of the molecules
Explanation: Molecular diffusion results from the random thermal motion of molecules, which produces a net movement down a concentration gradient.
Correct answer: Thermal energy of the molecules- A. Newtonian liquids
- B. Non-Newtonian liquids
- C. Real gases
- D. Ideal gases
Explanation: For a binary ideal-gas mixture, the mutual diffusivity is symmetric, so DAB equals DBA.
Correct answer: Ideal gases- A. For NtoG in absorption for dilute mixture
- B. Differential distillation equation
- C. Slope of q-line in McCabe-Thiele method
- D. For relative volatility
Explanation: The Rayleigh equation for differential, or batch, distillation is ln(F/W) = ∫ dx/(y* − x), with the limits determined by the initial and…
Correct answer: Differential distillation equation- A. Evaporation
- B. Drift
- C. All A., B. and C.
- D. Blowdown and leakage
Explanation: Cooling-tower makeup water replaces all major losses: evaporation, drift carried out with the air, and blowdown or leakage.
Correct answer: All A., B. and C.- A. Straight
- B. Parallel
- C. Neither A. nor B.
- D. Both A. & B.
Explanation: HETP becomes equal to HTUOG when the equilibrium and operating lines are straight and parallel, giving a constant driving force…
Correct answer: Both A. & B.- A. Operating line always lies below the equilibrium curve
- B. Operating line always lies above the equilibrium curve
- C. Temperature remains unaffected
- D. Temperature always increases
Explanation: In a stripper, the liquid transfers solute to the gas, and the operating line lies below the equilibrium curve on the usual y-x diagram.
Correct answer: Operating line always lies below the equilibrium curve- A. 1
- B. > 1
- C. < 1
- D. 0.5
Explanation: The absorption factor is A = L/(mV), and a value greater than one generally gives favorable absorption with sufficient liquid flow…
Correct answer: > 1- A. Hexane
- B. Hot water
- C. Lime water
- D. Dilute H2SO4 (hot)
Explanation: Hot water dissolves and extracts the soluble flavour, caffeine, and other components from coffee beans, whereas hexane is used mainly for…
Correct answer: Hot water- A. Packed
- B. Tray
- C. Spray
- D. Bubble
Explanation: A bubble column provides intense gas dispersion and a relatively large liquid inventory, giving high liquid holdup and long gas-liquid…
Correct answer: Bubble- A. Liquid film
- B. Gas film
- C. Liquid-gas interface
- D. None of these
Explanation: Carbon dioxide has limited solubility in water compared with highly soluble gases, so the liquid-side concentration gradient provides the…
Correct answer: Liquid film- A. Liquid
- B. Gas
- C. Both A. & B.
- D. Neither A. nor B.
Explanation: Ammonia is highly soluble in water, making the liquid-film resistance relatively small; the gas film usually provides the main resistance…
Correct answer: Gas- A. 5
- B. 30
- C. 60
- D. 100
Explanation: Large-diameter petroleum-refinery distillation columns commonly use tray spacings of about 24 to 36 inches.
Correct answer: 30- A. > 4 :1
- B. < 8 : 1
- C. < 6:1
- D. > 8:1
Explanation: Channelling is reduced when the tower is sufficiently wide relative to the packing, allowing liquid to redistribute instead of following…
Correct answer: > 8:1- A. Liquid extraction
- B. Distillation
- C. Evaporation
- D. Absorption
Explanation: Liquid extraction avoids the large vaporisation duty required by distillation, which is especially important for heat-sensitive materials…
Correct answer: Liquid extraction