chemical engineering mass transfer Mcqs
251. It takes 6 hours to dry a wet solid from 50% moisture content to the critical moisture content of 15%. How much longer it will take to dry the solid to 10% moisture content, under the same drying conditions? (The equilibrium moisture content of the solid is 5%) ?
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A. 51 min

B. 15 min

C. 94 min

D. 71 min
252. In a binary distillation column, if the feed contains 40 mole % vapour, the q line will have a slope of_________________?
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A. 1.5

B. 0.6

C. -0.6

D. -1.5
253. Flash distillation is _______________________?
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A. Same as simple distillation

B. Used for multi-component systems like crude refining

C. Most useful for handling binary systems

D. Same as differential distillation

254. Relative volatility varies with the concentration of component for an ideal solution. The relative volatility of a binary mixture may be defined as the ratio of vapor pressure of component A to that of component B, when_________________?
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A. Vapor phase obeys Daltons law and liquid phase obeys Raoults law

B. Liquid phase obeys Daltons law and vapor phase obeys Raoults law

C. Only vapor phase follows Raoults law

D. Only liquid phase obeys Daltons law

255. Alcohol is dehydrated using ______________ distillation?
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A. Extractive

B. Molecular

C. Azeotropic

D. Steam

256. In a gas-liquid absorption column, for obtaining the maximum absorption efficiency____________________?
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A. Liquid stream should be distributed uniformly

B. Gas stream should be distributed uniformly

C. Both gas as well as liquid streams should be distributed uniformly

D. By passing should be completely avoided

E. wer: Option C

257. For gas absorption, low viscosity solvents are preferred, because of their ____________________?
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A. Better flow characteristics

B. Rapid absorption rates

C. All A., B. and C.

D. Low pumping pressure drop

258. Freundlich equation applies to the adsorption of solute from___________________?
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A. Dilute solutions, over a small concentration range

B. Concentrated solutions

C. Gaseous solutions at high pressure

D. None of these

259. Rayleigh equation applies to _________________ distillation ?
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A. Molecular

B. Differential

C. Flash

D. Equilibrium

260. Penetration theory relates the average mass transfer co-efficient (K) with diffusivity D. as____________________?
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A. K ?D2

B. K ??D

C. K ?D

D. K ?D1.5

261. For a binary mixture with low relative volatility________________?
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A. An azeotrope may be formed during distillation

B. Use high pressure distillation

C. Use molecular distillation

D. Use steam distillation

262. In case of unsaturated air____________________?
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A. Dew point < wet bulb temperature

B. Wet bulb temperature < dry bulb temperature

C. Both A. and B.

D. Neither A. not B.

263. During sensible cooling process ______________________?
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A. Relative humidity decreases

B. Relative humidity increases

C. Wet bulb temperature decreases

D. Both B. and C.
264. Which of the following processes is followed by unsaturated air (with dry bulb temperature 12C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40C ?
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A. Humidification only

B. Heating only

C. Both heating and humidification

D. Evaporative cooling

265. Which of the following decreases during evaporative cooling process with recirculated water supply ?
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A. Wet bulb temperature

B. Partial pressure of vapour

C. None of these

D. Relative humidity

266. In case of physical adsorption, the difference between heat of adsorption and heat of normal condensation is__________________?
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A. Equal to the heat of wetting

B. Equal to the heat of formation of surface compound

C. Called integral heat of adsorption

D. Zero

267. In a vapor-liquid contacting equipment, the overall gas phase mass transfer co-efficient (M.T.C), KG is related to individual co-efficients (KG and KL) as ___________________ ?
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A. 1/KG = 1/KG + m/KL

B. KG = 1/KG + m/KL

C. KG = 1/KL + m/KG

D. 1/KG = 1/KL + m/KG

268. The slope of 9-line is determined by the______________________?
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A. Plate efficiency to be achieved

B. Reflux ratio

C. Thermal condition of the feed

D. Relative volatility

269. In an absorption column, the flooding velocity for random packing is ___________________ that for stacked/regular packing?
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A. Equal to

B. Either A., or B.; depends on the type of packing

C. Greater than

D. Smaller than
270. The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives___________________?
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A. Low pressure drop and high hold up

B. High pressure drop and high hold up

C. Low pressure drop and low hold up

D. High pressure drop and low hold up

271. For a binary mixture with low relative volatility___________________?
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A. Use molecular distillation

B. Use steam distillation

C. Use high pressure distillation

D. An azeotrope may be formed during distillation
272. Freundlich equation applies to the adsorption of solute from_____________________?
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A. Dilute solutions, over a small concentration range

B. None of these

C. Concentrated solutions

D. Gaseous solutions at high pressure

273. The slope of the operating line for a single component co-current absorber when plotted in terms of mole ratio units is_____________________?
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A. ?

B. -ve

C. 0

D. #NAME?

274. Calculation of mass transfer co-efficient is mostly/normally done using ______________ theory?
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A. Film

B. None of these

C. Penetration

D. Surface renewal

275. The relative saturation of a partially saturated mixture of vapour and gas can be increased by ________________ of the mixture?
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A. Reducing the total pressure

B. Increasing the total pressure

C. Reducing the temperature

D. Both B. and C.
276. An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii) ____________________?
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A. Less number of trays are required

B. Composition of the residue remains unchanged

C. More number of trays are required and the residue composition is more dilute in methanol

D. More number of trays are required but the residue composition remains unchanged

277. If the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be _______________ percent?
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A. 100

B. None of these

C. > 100

D. < 100

278. Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty ?
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A. Perforated tray tower

B. Wetted wall tower

C. Grid tray tower

D. Bubble cap tower
279. An air-water vapour mixture has a dry bulb temperature of 60C and a dew point temperature of 40C. The total pressure is 101.3 kPa and the vapour pressure of water at 40C and 60C are 7.30 kPa and 19.91 kPa respectively. The humidity of air sample expressed as kg of water vapour/kg of dry air is__________________?
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A. 0.048

B. 0.079

C. 0.122

D. 0.152
280. Humid volume is the total volume in m3 of 1 kg of _____________________?
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A. Vapour laden gas at 1 atm. and room temperature

B. Gas plus its accompanying vapour at 1 atm. and gas temperature

C. Gas plus its accompanying vapour at 1 atm. and room temperature

D. Vapour laden gas at 1 atm. and gas temperature

281. Desirable value of absorption factor in an absorber is___________________?
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A. > 1

B. < 1

C. 1

D. 0.5

282. Components, having widely different boiling point in a binary mixture, can be separated using ________________ distillation?
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A. Steam

B. Extractive

C. Molecular

D. Simple
283. The falling rate period in the drying of a solid is characterised by__________________?
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A. Increase in rate of drying

B. Increasing temperatures both on the surface and within the solid

C. Decreasing temperatures

D. None of these

284. According to the film theory of mass transfer, the mass transfer co-efficient is proportional to (where, D = molecular diffusivity) ?
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A. D2

B. D

C. D0.5

D. 1/D

285. The dew point of a saturated gas phase equals the ________________ temperature?
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A. Room

B. None of these

C. Wet bulb

D. Gas
286. For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as___________________?
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A. Re0.53

B. Re0.83

C. Re

D. Re0.33

287. Advantage of continuous drying over batch drying is that the_____________________?
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A. Equipment size required is smaller

B. Drying cost per unit weight of dried product is less

C. All A , B. & C.

D. Product with more uniform moisture content is produced

288. Surface renewal model of mass transfer was enunciated by___________________?
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A. Danckwerts

B. Fick

C. Toor and Marcello

D. Stefan

289. For a fixed number of ideal stages in a distillation column, as the reflux ratio is increased, the difference in composition between the top and bottom product streams__________________?
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A. Increases

B. Decreases

C. Remain unaffected

D. Passes through a maximum

290. ADDUCTS and CLATHRATES are used in case of_____________________?
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A. Absorption

B. Extractive distillation

C. Crystallisation

D. None of these

291. Separation of the isotopes of helium for scientific investigations is done by_____________________?
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A. Thermal diffusion

B. Solvent extraction

C. Reverse osmosis

D. Leaching

292. The wetted wall tower is used to determine_________________________?
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A. The overall M.T.C. of the system

B. M.T.C. of individual components in a liquid-liquid system

C. Individual mass transfer co-efficient (M.T.C.) in gaseous system

D. M.T.C. of liquid in liquid-gas system

293. Dry bulb temperature of the gas is _____________ the wet bulb temperature?
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A. Less than

B. Equal to

C. More than

D. None of these

294. Degree of freedom for leaching and solvent extraction process is_____________________?
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A. 1

B. 3

C. 0

D. 2

295. Flooding in a distillation column is detected by a sharp ___________________?
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A. Increase in pressure drop

B. Increase in Murphree plate efficiency

C. Decrease in liquid hold up in the column

D. Decrease in pressure drop

296. Drift in a cooling tower is ___________________?
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A. The water entrained by the circulating air

B. Dependent on the water lost by evaporation

C. Desirable

D. All A., B. & C.

297. Adsorption is a unit operation which generally involves _______________ systems?
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A. Fluid-solid

B. Gas-solid

C. Solid-solid

D. Liquid-solid

298. Use of raschig rings in place of crushed stones as packing in packed beds (other things being same) ?
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A. Increases pressure drop, decreases surface area

B. Decreases pressure drop, decreases surface area

C. Decreases pressure drop, increases surface area

D. Increases pressure drop, increases surface area

299. Make up water is required in a cooling tower to replace the water lost by___________________?
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A. Drift

B. Evaporation

C. Blowdown and leakage

D. All A., B. and C.
300. Nitrobenzene (boiling point = 210.6C) is steam distilled at 1 atm pressure. Nitrobenzene will distil off _______________ C?
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A. At < 100

B. Between 100 and 210

C. None of these

D. At > 210.6