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Refrigeration And Air Conditioning MCQ

Refrigeration And Air Conditioning MCQ Question and Answer

1.Nusselt number (NN) is given by

  • ANN = hl/k
  • BNN = μ cp/k
  • CNN = ρ V l /μ
  • DNN = V²/t.cp
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Correct Answer : (A)

NN = hl/k

Explanation:

2.In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

  • AB.P.F. – 1
  • B1 - B. P.F.
  • C1/ B.P.F.
  • D1 + B.P.F.
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Correct Answer : (A)

B.P.F. – 1

Explanation:

3.The undesirable property of a refrigerant is

  • ANon-toxic
  • BNon-flammable
  • CNon-explosive
  • DHigh boiling point
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Correct Answer : (D)

High boiling point

Explanation:

4.The desirable property of a refrigerant is

  • ALow boiling point
  • BHigh critical temperature
  • CHigh latent heat of vaporization
  • DAll of these
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Correct Answer : (A)

Low boiling point

Explanation:

5.The operating pressure for refrigerating units using R-12 as a refrigerant is

  • A2 bar
  • B8 bar
  • C15 bar
  • D30 bar
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Correct Answer : (B)

8 bar

Explanation:

6.Cooling water is required for following equipment in ammonia absorption plant

  • ACondenser
  • BEvaporator
  • CAbsorber
  • DCondenser, absorber and separator (rectifier)
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Correct Answer : (D)

Condenser, absorber and separator (rectifier)

Explanation:

7.The coefficient of performance of a domestic refrigerator is ________ as compared to a domestic air-conditioner.

  • ASame
  • BLess
  • CMore
  • DNone of these
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Correct Answer : (B)

Less

Explanation:

8.In aqua ammonia and Lithium bromide water absorption refrigeration systems, the refrigerants are respectively

  • AWater and water
  • BWater and lithium bromide
  • CAmmonia and lithium bromide
  • DAmmonia and water
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Correct Answer : (D)

Ammonia and water

Explanation:

9.In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature

  • AWhich lies between the dry bulb and wet bulb temperatures of the incoming stream
  • BWhich lies between the wet bulb and dew point temperatures of the incoming stream
  • CWhich is lower than the dew point temperature of the incoming stream
  • DOf adiabatic saturation of incoming stream
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Correct Answer : (C)

Which is lower than the dew point temperature of the incoming stream

Explanation:

10.During heating and dehumidification process, dry bulb temperature

  • ARemains constant
  • BIncreases
  • CDecreases
  • DNone of these
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Correct Answer : (B)

Increases

Explanation:

11.During cooling and dehumidification, dry bulb temperature

  • ARemains constant
  • BIncreases
  • CDecreases
  • DNone of these
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Correct Answer : (C)

Decreases

Explanation:

12.In a domestic vapour compression refrigerator, the refrigerant commonly used is

  • ACO
  • BAmmonia
  • CR-12
  • DAll of these
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Correct Answer : (C)

R-12

Explanation:

13.In refrigerators, the temperature difference between the evaporating refrigerant and the medium being cooled should be

  • AHigh, of the order of 25°
  • BAs low as possible (3 to 11°C)
  • CZero
  • DAny value
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Correct Answer : (B)

As low as possible (3 to 11°C)

Explanation:

14.The minimum temperature to which water can be cooled in a cooling tower is

  • ADew point temperature of air
  • BWet bulb temperature of air
  • CDry bulb temperature of air
  • DAmbient air temperature
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Correct Answer : (B)

Wet bulb temperature of air

Explanation:

15.Air refrigeration cycle is used in

  • ADomestic refrigerators
  • BCommercial refrigerators
  • CAir conditioning
  • DGas liquefaction
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Correct Answer : (D)

Gas liquefaction

Explanation:

16.A refrigeration cycle operates between condenser temperature of + 27°C and evaporator temperature of -23°C. The Carnot coefficient of performance of cycle will be

  • A0.2
  • B1.2
  • C5
  • D6
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Correct Answer : (C)

5

Explanation:

17.The bypass factor (B. P. F.) in case of sensible heating of air is (Where td₁ = Dry bulb temperature of air entering the heating coil, td₂ = Dry bulb temperature of air leaving the heating coil, and td₃ = Dry bulb temperature of heating coil)

  • A(td₂ - td₃)/(td₃ - td₁)
  • B(td₃ - td₂)/(td₃ - td₁)
  • C(td₃ - td₁)/(td₂ - td₃)
  • D(td₃ - td₁)/(td₃ - td₂)
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Correct Answer : (B)

(td₃ - td₂)/(td₃ - td₁)

Explanation:

18.The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

  • A0.1 to 0.5 h.p. per ton of refrigeration
  • B0.5 to 0.8 h.p. per ton of refrigeration
  • C1 to 2 h.p. per ton of refrigeration
  • D2 to 5 h.p. per ton of refrigeration
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Correct Answer : (C)

1 to 2 h.p. per ton of refrigeration

Explanation:

19.The freezing point of R-12 is

  • A-86.6°C
  • B-95.2°C
  • C-107.7°C
  • D-157.7°C
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Correct Answer : (D)

-157.7°C

Explanation:

20.The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by

  • A(C.O.P.)P = (C.O.P.)R + 2
  • B(C.O.P.)P = (C.O.P.)R + 1
  • C(C.O.P)P = (C.O.P)R – 1
  • D(C.O.P)P = (C.O.P)R
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Correct Answer : (B)

(C.O.P.)P = (C.O.P.)R + 1

Explanation: