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.
Last updated
669 questions · page 32 of 34
- A. Sherwood
- B. Grashoff
- C. Lewis
- D. None of these
Explanation: The Lewis number compares thermal diffusivity with mass diffusivity and therefore represents the relationship between heat and mass…
Correct answer: Lewis- A. Cooled
- B. Dehumidified
- C. Both A. & B.
- D. Humidified
Explanation: The spray water is at 35°C, equal to the air dry-bulb temperature, so it does not provide sensible cooling.
Correct answer: Humidified- A. Co-efficient = Flux/concentration difference
- B. Flux = Co-efficient/concentration difference
- C. Flux=concentration difference/coefficient
- D. None of these
Explanation: The mass-transfer coefficient is defined as the rate of mass flux divided by the driving concentration difference, so flux equals…
Correct answer: Co-efficient = Flux/concentration difference- A. Freeze
- B. Rotary vacuum
- C. Through circulation
- D. Tray
Explanation: Through-circulation dryers are suitable for drying large quantities of porous or granular solids such as silica gel because heated air…
Correct answer: Through circulation625. The value of „L/mG' ratio for economical absorption operation ranges from _____________________?
- A. 0.5 to 0.8
- B. 0.8 to 1.2
- C. 2.5 to 3.5
- D. 1.25 to 2.0
Explanation: For economical absorption, the liquid-to-gas flow ratio relative to the equilibrium-line slope, L/mG, is commonly maintained around 1.25…
Correct answer: 1.25 to 2.0- A. 6.89
- B. 8.89
- C. 10
- D. 8.25
Explanation: Overall balances give E + R = 40 and the solute balance gives 0.5E + 0.05R = 6. Substitution yields 0.45E = 4, so E = 8.89 kg.
Correct answer: 8.89- A. Rotary
- B. Tray
- C. Freeze
- D. None of these
Explanation: Tray dryers can produce nonuniform moisture because trays may experience unequal temperature, airflow, and drying conditions at different…
Correct answer: Tray- A. Temperature is 100°C
- B. Temperature is more than 100° C
- C. Product must be immiscible with water
- D. Temperature is higher than the boiling point of either component
Explanation: Steam distillation is used when the product is immiscible with water, allowing the combined vapour pressures to produce boiling below the…
Correct answer: Product must be immiscible with water- A. Dry bulb temperature
- B. Partial pressure of vapour
- C. Wet bulb temperature
- D. None of these
Explanation: During chemical dehumidification, the desiccant removes water vapour while the dry-bulb temperature is treated as approximately constant…
Correct answer: Dry bulb temperature- A. Cold water
- B. Hot water
- C. Dilute hot caustic solution
- D. Naphtha
Explanation: Coffee solubles are extracted from roasted and ground beans using hot water, which increases solubility and provides the required…
Correct answer: Hot water- A. Steady state diffusion for stagnant case
- B. Fick's first law of diffusion
- C. Steady state equimolar counter diffusion
- D. Liquid M.T.C. by penetration theory
Explanation: For steady equimolar counterdiffusion, the molar flux is proportional to the mole-fraction difference and inversely proportional to the…
Correct answer: Steady state equimolar counter diffusion- A. (De.t)1/2
- B. (De/t)1/2
- C. (4De/t)
- D. (4De/πt)1/2
Explanation: Higbie's penetration theory gives k_c = 2√(D_e/πt), which is equivalently √(4D_e/πt).
Correct answer: (4De/πt)1/2- A. Gas side co-efficient should be increased
- B. Liquid side coefficient should be increased
- C. Gas side co-efficient should be decreased
- D. Liquid side co-efficient should be decreased
Explanation: A sparingly soluble gas offers high resistance in the liquid film, so the liquid-side mass-transfer coefficient should be increased.
Correct answer: Liquid side coefficient should be increased- A. Free
- B. Equilibrium
- C. Unbound
- D. Bound
Explanation: Equilibrium moisture is the moisture content that remains in equilibrium with a specified vapour partial pressure.
Correct answer: Equilibrium- A. Remain same
- B. Decreases
- C. Increases
- D. Either A. or B.; depends on the gas
Explanation: Knudsen permeability depends on molecular thermal speed, which varies as √T.
Correct answer: Increases636. The Knudsen diffusivity is proportional to (where, T = absolute temperature) ______________________?
- A. T4
- B. T2
- C. T
- D. √T
Explanation: Knudsen diffusivity is governed by molecular speed inside the pores: D_K is proportional to √(T/M).
Correct answer: √T637. Which of the following processes is not an example of adsorption applied to gaseous separations ?
- A. Decolouration of yellow glycerine
- B. Dehumidification of air and gas
- C. Removal of objectionable odour and impurities from industrial gases
- D. Recovery of valuable solvent vapors from dilute mixture with air and other gases
Explanation: Decolouration of yellow glycerine is adsorption from a liquid, commonly using activated carbon, rather than separation from a gas.
Correct answer: Decolouration of yellow glycerine- A. Highly humid
- B. Perfectly dry
- C. High temperature
- D. None of these
Explanation: Complete removal of moisture requires air with zero moisture content, because any water vapour in the air establishes a nonzero…
Correct answer: Perfectly dry- A. G/(FG . a)
- B. FG/(G . a)
- C. (G . a)/FG
- D. L/(FG . G)
Explanation: The gas-phase height of a transfer unit is H_G = G/(F_G a), obtained by dividing the gas molar velocity by the volumetric gas-side…
Correct answer: G/(FG . a)- A. Higher contact area
- B. Better contact of the phase
- C. Repeated coalescence & redispersion of the drop phase
- D. None of these
Explanation: Perforated plates repeatedly break up, coalesce, and redisperse the dispersed drops as they pass through the plates.
Correct answer: Repeated coalescence & redispersion of the drop phase