chemical engineering mass transfer Mcqs
351. Molecular diffusion is caused by the________________?
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A. Potential energy of the molecules

B. Transfer of molecules from low concentration to high concentration region

C. Thermal energy of the molecules

D. Activation energy of the molecules

352. Which of the following operations does not involve leaching ?
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A. Dissolving pharmaceutical products from bark or roots

B. Dissolving gold from ores

C. Removing nicotine from its water solution by kerosene

D. Dissolving sugar from the cells of the beet

353. The caking of crystals can be prevented by _____________________?
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A. Maintaining high critical humidity

B. Maintaining low critical humidity

C. Coating the product with inert material

D. Both A. and C.
354. The equipment used in the extraction of highly corrosive radioactive liquids is_______________________?
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A. Pulse column

B. Spray column

C. Baffle tower

D. Mixer settler

355. In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer?
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A. Less than 2 kg but more than 1 kg of C is transferred to solvent B

B. Less than 1 kg of C is transferred to B

C. No amount of C is transferred to B

D. The entire amount of C is transferred to solvent B
356. Stefans law describes the mass transfer by________________?
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A. Diffusion

B. Bulk flow

C. Both A. & B.

D. Neither A. nor B.

357. Which of the following employs an accessory known as drift eliminator ?
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A. Rotating disc contactor

B. Multiple effect evaporator

C. Mechanical draft cooling tower

D. Rotary dryer

358. If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that___________________?
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A. The system comprises of miscible liquids

B. The system comprises of an azeotrope

C. On heating, a vapor phase will appear; while on cooling, a solid phase will appear

D. The system comprises of partially miscible liquids

359. If f = moles of vapour present per mole of feed, then the slope of feed line is (McCabe- Thiele method) ________________________?
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A. -1/f

B. -f/(1 f)

C. (1 f)/f

D. (f 1)/f

360. With increase in temperature, the rate of extraction in leaching (solid-liquid extraction system) ?
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A. Increases Linearly

B. Increases

C. Remain unaffected

D. Decreases

361. In a counter-current liquid extractor___________________?
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A. Both liquids flow at fixed rate

B. Both liquids can have any desired flow rate

C. Only one of the liquids may be pumped at any desired rate

D. Liquids flow rate depends upon the temperature and pressure

362. Liquid diffusivity is of the order of _______________ cm2 /second?
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A. > 1

B. 10-5 to 10-6

C. 0.1

D. 0.01

363. Air initially at 101. 3 kPa and 40C and with a relative humidity of 50%, is cooled at constant pressure to 30C. The cooled air has a____________________?
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A. Higher wet bulb temperature

B. Higher relative humidity

C. Higher absolute (specific) humidity

D. Higher dew point

364. At what value of reflux ratio, number of theoretical plates in a distillation column is minimum ?
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A. < 1

B. ?

C. 0

D. 1

365. Back-trapping in a distillation column ?
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A. Increases tray efficiency

B. Is desirable, as it provides improved vapour-liquid contact

C. Reduces pressure drop

D. Decreases tray efficiency
366. In which of the following unit operations, the selectivity is an important parameter ?
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A. Solvent extraction

B. Absorption

C. None of these

D. Distillation

367. In distillation, overhead product contains ______________________?
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A. Any number of components

B. Two components

C. Only one component

D. Only saturated liquid

368. The suitable evaporator for concentration of foaming liquids is a ______________________ evaporator?
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A. Short tube

B. Vacuum

C. Long tube

D. Falling film

369. To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate) ____________________?
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A. Increase both G and S

B. Decrease both G and S

C. Increase S and decrease G

D. Increase G and decrease S

370. At __________________ reflux, theoretical number of plates in a distillation coloumn is calculated using Fenske-Underwood equation?
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A. Minimum

B. Operating

C. Maximum permissible

D. Total
371. In liquid-liquid extraction, the number of phases at plait point is __________________?
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A. 3

B. 1

C. 2

D. 4

372. Penetration model (theory) for mass transfer was enunciated by _____________________?
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A. Higbie

B. Kissinevskii

C. Toor and Marcello

D. Danckwerts

373. If f is defined as above, then which of the following applies to a feed at dew point ?
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A. 0 < f < 1

B. f 1

C. f = 1
374. Bollman extractor___________________?
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A. Is a static bed leaching equipment

B. Is used for extraction of oil from oilseed

C. Employs only counter-current extraction

D. Is a centrifugal extractor

375. In case of liquids, the binary diffusivity is proportional to (where, T = temperature) _____________________?
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A. 1/T

B. T

C. T2

D. ?T

376. Rotary dryers cannot handle _______________ materials ?
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A. Sticky

B. Dry

C. Granular

D. Free flowing

377. 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___________________?
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A. None of these

B. Nsh = 2

C. Nst = 2

D. Nsc = 2

378. Absorption accompanied with chemical reaction is exemplified by the absorption of___________________?
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A. Benzol present in coke oven gas by wash oil

B. SO2 in alkaline solution

C. All A., B. and C.

D. Ammonia in water

379. Unit operation involved in the prilling of urea is_____________________?
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A. Evaporation

B. Drying

C. Crystallisation

D. Both B. and C.
380. Which of the following plays an important role in problems of simultaneous heat and mass transfer ?
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A. Sherwood number

B. Prandtl number

C. Lewis number

D. Schmidt number

381. With lapse of time, the overhead composition of light component in case of batch distillation with constant reflux__________________?
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A. Increases

B. Remain same

C. May increase or decrease; depends on system

D. Decreases
382. The most economical range of absorption factor is____________________?
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A. 0 to 3

B. 5 to 15

C. 1.25 to 2

D. 0 to 0.5

383. The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by __________________?
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A. Raising the temperature

B. Lowering the total pressure

C. Both A. and B.

D. Neither A. nor B.

384. As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches ____________________?
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A. That of normal condensation

B. None of these

C. Zero

D. Integral heat of adsorption

385. ______________ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction ?
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A. Packed

B. Bubble

C. Spray

D. Tray

386. The adiabatic saturation curve for a vapour-gas mixture is__________________?
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A. None of these

B. Slightly concave upward

C. Straight line

D. Slightly concave downward

387. The recovery of penicillin from the acidified fermentation broth is done by__________________?
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A. Distillation

B. Evaporation

C. Absorption

D. Liquid extraction
388. The relative saturation of an unsaturated mixture of gas and vapor is independent of the___________________?
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A. None of these

B. Temperature of the mixture

C. Composition of the mixture

D. Nature of the vapor

389. Which of the following is not a continuous drier ?
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A. Spray drier

B. Drum drier

C. Tunnel drier

D. Tray drier
390. With increase in the concentration of the adsorbate, the integral heat of adsorption____________________?
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A. May increase or decrease; depends on the type of adsorbate

B. Remains unchanged

C. Decreases

D. Increases

391. Wet bulb and dry bulb temperatures becomes identical at _______________ percent saturation curve?
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A. None of these

B. 100

C. 50

D. 78

392. A coalescer in a mixer-settler liquid-liquid extraction column______________________?
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A. Comprises of thin bed of substances of extended surface having high porosity

B. All a, b, & c

C. Helps in increasing the bubble size entering the settler

D. Helps in increasing the settling rate of the bubbles

393. Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in ______________ tower?
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A. Packed

B. Wetted wall

C. Perforated tray

D. Bubble cap

394. NSc/NPr is called the______________________?
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A. Sherwood number

B. Stanton number

C. Lewis number

D. Psychrometric ratio

395. Mass transfer co-efficient varies as DAB 0.5, according to the _______________ theory?
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A. Film

B. Surface renewal

C. None of these

D. Penetration

396. Compound A is extracted from a solution of A + B into a pure solvent S. A Co-current unit is used for the liquid-liquid extraction. The inlet rate of the solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400 moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y is in moles of a A/moles of B and X is in moles A/moles of S. The maximum percentage extraction achieved in the unit is_________________________?
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A. 70%

B. 50%

C. 25%

D. 90%

397. Batch tray dryers suffers from the disadvantage of______________________?
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A. High maintenance cost

B. High labour cost & low heat economy

C. Non-uniform & low production rate

D. All a, b & c

398. In case of an ideal solution, the total vapor pressure varies ______________ with the composition expressed as mole fraction?
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A. Exponentially

B. Inversely

C. None of these

D. Linearly
399. The equilibrium liquid composition compared to the vapor composition in case of________________?
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A. More

B. Either more or less; depends on the system

C. Same

D. Less

E. otropic mixture is

400. When the psychometric ratio is ______________ then the adiabatic saturation temperature and wet bulb temperature becomes equal?
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A. 1

B. ?

C. 1