Refrigeration and Air Conditioning

21. Critical temperature is' the temperature above which

  1. a gas will never liquefy
  2. a gas will immediately liquefy
  3. water will evaporate
  4. water will never evaporate
  5. none of the above.

Correct answer: (A)
a gas will never liquefy

22. Domestic refrigerator working on vapour compression cycle uses the following type of expansion device

  1. electrically operated throttling valve
  2. manually operated valve
  3. thermostatic valve
  4. capillary tube
  5. expansion valve.

Correct answer: (D)
capillary tube

23. Efficiency of a Cornot engine is given as 80%. If the- cycle direction be reversed, what will be the value of COP of reversed Carnot cycle

  1. 1.25
  2. 0.8
  3. 0.5
  4. 0.25
  5. none of the above.

Correct answer: (D)
0.25

24. For better COP of refrigerator, the pressure range corresponding to temperature in evaporator and condenser must be

  1. small
  2. high
  3. euqal
  4. anything
  5. under some conditions small and under some conditions high.

Correct answer: (A)
small

25. For obtaining high COP, the pressure range of compressor should be

  1. high
  2. low
  3. optimum
  4. any value
  5. there is no such criterion.

Correct answer: (B)
low

26. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then

  1. bigger cabinet should be used
  2. smaller cabinet should be used
  3. perfectly tight vapour seal should be used
  4. refrigerant with lower evaporation temperature should be used
  5. refrigerant with high boiling point must be used.

Correct answer: (C)
perfectly tight vapour seal should be used

27. Formation of frost on evaporator in refrigerator

  1. results in loss of heat due to poor heat transfer
  2. increases heat transfer rate
  3. is immaterial
  4. can be avoided by proper design
  5. decreases compressor power.

Correct answer: (A)
results in loss of heat due to poor heat transfer

28. Freon group of refrigerants are

  1. inflammable
  2. toxic
  3. non-inflammable and toxic
  4. non-toxic and inflammable
  5. non-toxic and non-inflammable.

Correct answer: (E)
non-toxic and non-inflammable.

29. Highest pressure encountered in a refrigeration system should be

  1. critical pressure of refrigerant
  2. much below critical pressure
  3. much above critical pressure
  4. near critical pressure
  5. there is no such restriction.

Correct answer: (B)
much below critical pressure

30. Highest temperature encountered in refrigeration cycle should be

  1. near critical temperature of refrigerant
  2. above critical temperature
  3. at critica. temperature
  4. much below critical temperature
  5. could be anywhere.

Correct answer: (D)
much below critical temperature

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