chemical engineering mechanical operations Mcqs
251. If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the __________________?
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A. Dispersion

B. Flocculation

C. Centrifugation

D. Sedimentation

252. In case of a hammer crusher, the final product size depends on the____________________?
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A. All A., B. and C.

B. Feed rate

C. Clearance between hammer & grinding plates

D. Rotor speed

253. Work index is the gross energy (kWh/tonne of feed) necessary to reduce a very large feed to such a size that 80% of product particles will pass through a 0.1 mm screen. The value of work index determined for wet grinding should be multiplied with ______________ to get the same for dry grinding?
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A. 0.5

B. 1

C. 4.34

D. 1.34
254. The capacity of a pneumatic conveying system depends upon the ______________________?
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A. All A., B. and C.

B. Diameter of the conveying line

C. Bulk density of materials

D. Pressure of the conveying air

255. 200 mesh sieve size corresponds to _____________ microns?
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A. 154

B. 74

C. 200

D. 24

256. Ball mill is used for__________________?
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A. Fine grinding

B. Crushing

C. Attrition

D. Coarse grinding

257. A sand mixture was screened through a standard 10-mesh screen. The mass fraction of the oversize material in feed, overflow and underflow were found to be 0.38, 0.79 and 0.22 respectively. The screen effectiveness based on the oversize is_________________?
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A. 0.68

B. 0.50

C. 0.58

D. 0.62

258. A cottrell precipitator makes use of the ______________ for dusty air cleaning?
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A. Alternating current

B. Corona discharge

C. None of these

D. Electric spark

259. The value of work index does not change materially from one equipment to another. If the value of work index determined for close circuit grinding is Wi, then the same for open circuit grinding will be_________________?
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A. 3.34 Wi

B. Wi

C. 0.5 Wi

D. 1.34 Wi
260. Size reduction of fibrous materials like wood, asbestos, mica etc. is done by a disintegrator exemplified by the _________________?
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A. Stamp mill

B. Bradfords breaker

C. Cage mill

D. Blake jaw crusher

261. In a size reduction crushing operation, the feed size is 10 to 50 mm, while the product size is 2 to 10 mm. This is a case of _______________ crushing?
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A. Secondary

B. Ultrafine

C. Fine

D. Primary

262. For spheres, the surface shape factor is given by (where, A = area, V = volume, and D = diameter) ?
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A. AD/V

B. None of these

C. ? = (A/D2)

D. ?/6 = (V/D3)

263. Specific surface area is the surface area of a unit _______________ of materials?
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A. Either A. or B.

B. Volume

C. Neither A. nor B.

D. Weight

264. Velocity of a small particle of diameter Dp at a distance r from the rotational axis of a cyclone rotating at an angular speed ? is given by (the other symbols are as per standard notation) ?
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A. [(DP2/18). (?s ?/?)] ?2r

B. [(DP2/18). (?s ?/?)] ?2r

C. [(DP/18). (?s ?/?)] ?2r2

D. [(DP/18). (?s ?/?)] ?2r

265. The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a __________________?
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A. Sharpies centrifuge

B. None of these

C. Boundary mixer

D. Propeller agitator

266. Maximum size reduction in a ball mill is done by the, ______________ action?
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A. Cutting

B. Impact

C. Attrition

D. Compression

267. Which of the following is not used as a surface active agent in a flocculation operation ?
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A. Alumina

B. Quartz

C. Sodium silicate

D. Lime

268. _____________ Centrifuge is normally used in sugar mills?
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A. Suspended batch basket

B. Disc-bowl

C. Tubular bowl

D. Perforated horizontal basket continuous

269. Mixer used for rubber compounding is__________________?
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A. Pug mill

B. Muller mixer

C. Banbury internal mixer

D. mixer-extruder

270. Separation of materials into products based on the difference of their sizes is called___________________?
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A. Sizing

B. Flocculation

C. Classification

D. Sorting

271. Balls for ball mills are never made of_________________?
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A. Alloy steel

B. Forged/cast steel

C. Cast iron

D. Lead
272. For spheres, volume shape factor is given by____________________?
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A. ? = (A/D2)

B. 2? = (2A/D2)

C. AD/V

D. ?/6 = (V/D3)
273. Grizzlies are used for separating _____________ solids?
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A. Coarse

B. Any size

C. None of these

D. Fine
274. In a mixer, the quantity, (v. L/D) is termed as __________ number (where, v = longitudinal velocity of material, L = length of the mixer, D = diffusivity in axial mixing) ?
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A. Schmidt

B. Weber

C. Brinkman

D. Peclet
275. Diatomaceous earth is a/an_________________?
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A. Catalyst

B. Explosive

C. Filter aid

D. Filter medium

276. A pebble mill_________________?
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A. Is a ball mill

B. Employs flints or ceramic pebbles as the grinding medium

C. Is a tube mill lined with ceramic or other non-metallic liner

D. Both B. and C.
277. What is the selectivity index, if the grade of tailings & concentrate is the same ?
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A. 1

B. 0

C. 0.5

D. ?

278. Metallic wire mesh is used as a filtering medium for the separation of dust from dust laden gas in case of a/an________________?
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A. Hydrocyclones

B. Air filter

C. Venturi scrubber

D. Bag filter

279. Mixing of light fine powder such as insecticides is done by____________________?
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A. Impact wheels

B. Pug mill

C. Kneader

D. Banbury mixer

280. Production rate _____________ with increased fineness, with a given energy input to the size reduction machine?
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A. May increase or decrease; depends on the machine

B. Remains unchanged

C. Decreases

D. Increases

281. A _____________ mixer resembles a ball mill without balls?
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A. Pug mill

B. Tumbling

C. Banbury

D. Pan

282. Which of the following minerals is not subjected to magnetic separation method ?
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A. Siderite

B. Galena

C. Rutile

D. Chromite

283. Mass flow of granular solid (M) through a circular opening of dia, D follows_____________________?
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A. M ? D2

B. M ? ?D

C. M ? D3

D. M ? D

284. A belt conveyor used for the transportation of materials can___________________?
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A. Run upto 1 km

B. Travel at a speed upto 300 metres/minute

C. Handle materials upto 5000 tons/hr

D. All A., B. and C.
285. Which of the following screens has the maximum capacity ?
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A. Trommels

B. Shaking screen

C. Grizzlies

D. Vibrating screen
286. Filtration should be stopped in a filter press, if the_________________?
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A. Cake becomes very dense

B. Liquor stops flowing out to the discharge

C. Filtration pressure rises suddenly

D. Both B. & C.
287. Choke crushing (in case of a Jaw crusher) compared to free crushing__________________?
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A. Results in increased capacity

B. Consumes less power

C. Consumes more power

D. Both A. and C.

288. Stamp mills are generally used for crushing__________________?
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A. Gold ores

B. Diamond

C. Talc

D. Iron ores

289. Rod mills employed for grinding_________________?
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A. Is useful for handling sticky materials

B. Employ a steel shell having L/D ratio of 1.5 to 3.0

C. Employ steel rods of 2-12 cms diameter extending over full length of the mill

D. All A , B & C
290. In a roll crusher, the specific power consumption and the production rate is affected by the_________________?
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A. Reduction ratio

B. Differential roll speed

C. Both A. and B.

D. Neither A. nor B.

291. Out of the following size reduction equipments, the maximum feed size can be accepted by the__________________?
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A. Tube mill

B. Jet pulveriser

C. Jaw crusher

D. Ball mill

292. Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a ______________ conveyor?
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A. Flight

B. Ribbon

C. Screw

D. Slat or drag

293. A _____________ mill is a revolving mill divided into two or more sections by perforated partitions in which preliminary grinding takes place at one end and the finishing grinding at the discharge end?
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A. Tube

B. Pebble

C. Rod

D. Compartment
294. Pick out the correct statement?
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A. The capacity and the effectiveness of a screen are the same

B. The capacity and the effectiveness of screen are opposing factors

C. The screening surface of a reel (a revolving screen used in flour mills) is made of silk bolting

D. th supported by wire mesh

E. Both B. and C.
295. To produce talcum powder, use_____________________?
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A. Ball mill

B. Jet mill

C. Hammer mill

D. Pin mill

296. The mechanism of size reduction by a hammer mill is by impact and attrition between the________________?
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A. Grinding element & the housing

B. Feed particles

C. Both A. and B.

D. Neither A. nor B.

297. Additives used for promoting the flocculation of particles is a/an _____________________?
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A. Electrolyte

B. Surface active agent

C. Both A. & B.

D. Neither A. nor B.

298. Ultrafine grinders operate principally by_________________?
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A. Impact

B. Slow compression

C. Attrition

D. Cutting action

299. Pebble mills are tumbling mills widely used for grinding in the manufacture of paints & pigments and cosmetic industries, where iron contamination in the product is highly objectionable. Pebbles used in pebble mill are made of__________________?
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A. Concrete

B. Flint or porcelain

C. Stainless steel

D. Bronze

300. Dust laden air can be purified using a____________________?
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A. Gravity settler

B. Bag filter

C. Tubular centrifuge

D. Cyclone separator