mechanical engineering MCQs – Page 86

Practise multiple-choice questions from mechanical engineering for competitive examinations and subject revision. Review each marked answer and report any item that may be outdated or unclear.

4251. Where does the lowest temperature occur in a vapour compression cycle ?
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A. condenser

B. evaporator

C. receiver

D. expansion valve

E. compressor

4252. In a refrigeration system, heat absorbed in comparison to heat rejected is_________________?
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A. more

B. less for small capacity and more for high capacity

C. less

D. more for small capacity and less for high capacity

E. same

4253. Choose the wrong statement ?
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A. Temperature of medium being cooled must be below that of the evaporator

B. frost on evaporator reduces heat transfer

C. refrigerant is circulated in a refrigeration system to transfer heat

D. All solar thermally operated absorption systems are capable only of intermittent operation

E. Refrigerant leaves the condenser as liquid

4254. Which of the following is not a desirable property of a refrigerant_________________?
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A. non-inflammable

B. low boiling point

C. good electrical conductor

D. high triiscibility with oil

E. large latent heat

4255. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant_________________?
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A. remains same

B. depends on other factors

C. none of the above

D. decreases

E. increases
4256. In a vapor compression cycle, the refrigerant immediately after expansion valve is___________________?
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A. wet vapour

B. saturated liquid

C. liquid

D. dry vapour

E. sub-cooled liquid

4257. Pick up the incorrect statement?
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A. weak solution in liquid heat exchanger gives up heat to the strong solution

B. lithium bromide plant cant operate below 0C

C. lithium bromide used in vapour absorption cycle is nonvolatile

D. concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator

E. a separator is used in lithium bromide plant to remove the unwanted water vapour by condensing
4258. Formation of frost on evaporator in refrigerator ________________?
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A. decreases compressor power

B. increases heat transfer rate

C. is immaterial

D. can be avoided by proper design

E. results in loss of heat due to poor heat transfer
4259. Absorption system normally uses the following refrigerant___________________?
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A. Freon-22

B. C02

C. ammonia

D. Freon-11

E. S02

4260. Choose the correct statement?
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A. Superheat and sensible heat of a. refrigerant are same

B. If operating temperature of system is low, then refrigerant with low boiling point should be used

C. Precooling and subcooling bf refrigerant are same

D. Refrigerant is inside the lubes in case of a direct-expansion chiller

E. A refrigerant should have low latent heat

4261. Highest pressure encountered in a refrigeration system should be________________?
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A. near critical pressure

B. there is no such restriction

C. much below critical pressure

D. much above critical pressure

E. critical pressure of refrigerant

4262. Highest temperature encountered in refrigeration cycle should be________________?
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A. could be anywhere

B. much below critical temperature

C. above critical temperature

D. near critical temperature of refrigerant

E. at critica. temperature

4263. If the evaporator temperature of a plant is lowered, keeping the condenser temperature constant, the h.p. of compressor required will be________________?
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A. more

B. more/less depending on rating

C. less

D. same

E. unpredictable

4264. One of the purposes of sub-cooling the liquid refrigerant is to________________?
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A. ensure that only liquid and not the vapour enters the expansion (throttling) valve

B. reduce compressor discharge temperature

C. reduce compressor overheating

D. increase cooling effect

E. none of the above

4265. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is________________?
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A. Ammonia

B. Carbon dioxide

C. Freon

D. Brine

E. Hydrocarbon refrigerant

4266. Pick up the correct statement about giving up of heat from one medium to other in ammonia absorption system ?
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A. ammonia vapour to strong solution

B. strong solution to weak solution

C. weak solution to strong solution

D. strong solution to ammonia vapour

E. ammonia vapour to weak solution