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 21 of 34
- A. Agitated vessels
- B. Packed towers
- C. Venturi scrubbers
- D. Wetted wall towers
Explanation: Agitated vessels are conventionally classified mainly as gas-dispersion or mechanically mixed contactors, whereas wetted-wall, packed, and…
Correct answer: Agitated vessels- A. Thermal diffusivity
- B. Mass transfer co-efficient
- C. Kinematic viscosity
- D. Volumetric diffusivity
Explanation: The diffusion coefficient has units of m²/s, like thermal diffusivity, kinematic viscosity, and volumetric diffusivity.
Correct answer: Mass transfer co-efficient- A. > 1 and ≈ 1
- B. 1 and 0
- C. < 1 and ≈ 1
- D. 0 and ≈ 1
Explanation: For air, the Schmidt number is approximately 0.7, hence less than one, while the Lewis number is close to unity because mass and thermal…
Correct answer: < 1 and ≈ 1- A. Increasing temperatures both on the surface and within the solid
- B. Increase in rate of drying
- C. Decreasing temperatures
- D. None of these
Explanation: During the falling-rate period, the surface is no longer fully wet, so evaporation resistance increases and the surface and interior…
Correct answer: Increasing temperatures both on the surface and within the solid- A. 4
- B. 8
- C. 9
- D. 10
Explanation: For 98% recovery, the outlet acetone fraction is 2% of 0.05, or 0.001. Thus N + 2 = 6 log10(0.05/0.001) ≈ 10.19, giving N ≈ 8.19, so 9…
Correct answer: 9- A. Unidirectional diffusion from liquid to gas phase
- B. Unidirectional diffusion from gas to liquid phase
- C. Either A. or B.
- D. A counter diffusion at an almost equal molar rate
Explanation: In binary distillation, both components diffuse across the gas-liquid interface in opposite directions.
Correct answer: A counter diffusion at an almost equal molar rate- A. Silica gel
- B. Alumina
- C. Fuller's earth
- D. Activated carbon
Explanation: Activated carbon has a highly developed porous surface and strongly adsorbs coloured organic impurities, so it is commonly used to…
Correct answer: Activated carbon- A. Danckwerts
- B. Fick
- C. Toor and Marcello
- D. Stefan
Explanation: Danckwerts proposed the surface-renewal model, which treats fluid elements at an interface as being randomly replaced by fresh elements…
Correct answer: Danckwerts409. If Rm is the minimum reflux ratio, the optimum reflux ratio may be around _________________ Rm ?
- A. 2.5 to 3
- B. 1.2 to 1.5
- C. 3 to 4
- D. 5
Explanation: Operating at the minimum reflux ratio requires an impractically large number of stages, while very high reflux gives excessive energy use.
Correct answer: 1.2 to 1.5- A. Sherwood
- B. Lewis
- C. Stanton
- D. Peclet
Explanation: The Lewis number compares thermal diffusivity with mass diffusivity and therefore relates the rates of heat and mass transfer in…
Correct answer: Lewis411. Gaseous diffusivity at atmospheric pressure is of the order of _____________________ cm2/second?
- A. > 10
- B. 1 to 5
- C. 5 to 10
- D. 1
Explanation: Gas diffusivities at about atmospheric pressure are typically of the order of 1 cm²/s, much larger than liquid diffusivities.
Correct answer: 1- A. The water entrained by the circulating air
- B. Dependent on the water lost by evaporation
- C. Desirable
- D. All A., B. & C.
Explanation: Drift is the mechanical carryover of tiny liquid-water droplets with the air leaving a cooling tower.
Correct answer: The water entrained by the circulating air- A. Lies below the equilibrium line
- B. And equilibrium lines are parallel
- C. Lies above the equilibrium line
- D. Is far from the equilibrium line
Explanation: When the operating and equilibrium lines are parallel, the driving-force relationship remains uniform in the relevant graphical treatment…
Correct answer: And equilibrium lines are parallel- A. Increases
- B. Remains unchanged
- C. Decreases
- D. Increases exponentially
Explanation: Adsorption is usually exothermic, so increasing temperature promotes desorption and lowers the amount adsorbed at a fixed equilibrium…
Correct answer: Decreases- A. Anthracite coal
- B. Rag paper
- C. Inorganic solids
- D. Bamboo
Explanation: Bamboo is a hygroscopic, porous material, so it retains more bound moisture at equilibrium than anthracite coal or inorganic solids.
Correct answer: Bamboo- A. Molecular
- B. Simple
- C. Steam
- D. Extractive
Explanation: Simple distillation is suitable when the components have widely different boiling points, because the more volatile component vaporizes…
Correct answer: Simple- A. Varies inversely as the pressure
- B. Varies directly as the pressure
- C. Is independent of pressure
- D. Is equal to the volumetric diffusivity
Explanation: Molal diffusivity is defined on a molal or chemical-potential basis, which accounts for non-ideal behaviour rather than following the…
Correct answer: Is independent of pressure- A. cm2/sec gm . mole
- B. gm moles/cm2 . sec
- C. gm moles/cm. sec
- D. gm moles/cm2. sec
Explanation: Molal diffusivity is a concentration-weighted diffusivity, so its units are molar concentration multiplied by diffusivity: (gm…
Correct answer: gm moles/cm. sec- A. Spray
- B. Freeze
- C. Tray
- D. Rotary
Explanation: Milk is commonly dried in a spray dryer, where atomized droplets contact hot air and dry rapidly.
Correct answer: Spray- A. Danckwerts
- B. Higbie
- C. Toor and Marcello
- D. Kissinevskii
Explanation: Higbie proposed the penetration theory, which models mass transfer as occurring during brief exposure of fresh fluid elements to an…
Correct answer: Higbie