300+ Top Refrigeration & Air Conditioning MCQs & Answers

Refrigeration and Air Conditioning Multiple Choice Questions

1. In vapour compression cycle using NH₃ as refrigerant, initial charge is filled at

A. Suction of compressor

B. Delivery of compressor

C. High pressure side close to receiver

D. Low pressure side near receiver

Answer: C

2. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called

A. Wet bulb temperature

B. Dry bulb temperature

C. Dew point temperature

D. None of these

Answer: B

3. Absorption system normally uses the following refrigerant

A. Freon-11

B. Freon-22

C. CO2

D. Ammonia

Answer: D

4. Which of the following statement is correct?

A. In vapour absorption refrigerator, the compression of refrigerant is avoided.

B. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.

C. In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

D. All of the above

Answer: D

5. In a refrigeration cycle, the flow of refrigerant is controlled by

A. Compressor

B. Condenser

C. Evaporator

D. Expansion valve

Answer: D

6. The colour of the flame of halide torch, in case of leakage of Freon refrigerant, will change to

A. Bright green

B. Yellow

C. Red

D. Orange

Answer: A

7. For air conditioning the operation theater in a hospital, the percentage of outside air in the air supplied is

A. Zero

B. 20

C. 50

D. 100

Answer: D

8. Allowable pressure on high pressure side or ammonia absorption system is of the order of

A. Atmospheric pressure

B. Slightly above atmospheric pressure

C. 24 bars

D. 56 bars

Answer: D

9. The C.O.P. of a Carnot refrigerator in winter will be _________ as compared to C.O.P. in summer.

A. Same

B. Lower

C. Higher

D. None of these

Answer: C

10. Chaperon equation is a relation between

A. Temperature, pressure and enthalpy

B. Specific volume and enthalpy

C. Temperature and enthalpy

D. Temperature, pressure, specific volume and enthalpy

Answer: D

Refrigeration & Air Conditioning MCQs

11. During humidification process, __________ increases.

A. Wet bulb temperature

B. Relative humidity

C. Dry bulb temperature

D. Specific humidity

Answer: B

12. Where does the lowest temperature occur in a vapour compression cycle?

A. Condenser

B. Evaporator

C. Compressor

D. Expansion valve

Answer: B

13. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure, is called

A. Humidity ratio

B. Relative humidity

C. Absolute humidity

D. Degree of saturation

Answer: B

14. Under cooling in a refrigeration cycle

A. Increases C.O.P

B. Decreases C.O.P

C. C.O.P remains unaltered

D. Other factors decide C.O.P

Answer: A

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

A. CO₂

B. Ammonia

C. R-12

D. All of these

Answer: C

16. The COP of a vapour compression plant in comparison to vapour absorption plant is

A. More

B. Less

C. Same

D. More/less depending on size of plant

Answer: A

17. The fluids used in Electrolux refrigerator are

A. Water and hydrogen

B. Ammonia and hydrogen

C. Ammonia, water and hydrogen

D. None of these

Answer: C

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

A. Electrically operated throttling valve

B. Manually operated valve

C. Thermostatic valve

D. Capillary tube

Answer: D

19. The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is

A. High pressure saturated liquid

B. Wet vapour

C. Very wet vapour

D. Dry vapour

Answer: C

20. An important characteristic of absorption system of refrigeration is

A. Noisy operation

B. Quiet operation

C. Cooling below 0°C

D. Very little power consumption

Answer: B

21. The centrifugal compressors are generally used for refrigerants that require

A. Small displacements and low condensing pressures

B. Large displacements and high condensing pressures

C. Small displacements and high condensing pressures

D. Large displacements and low condensing pressures

Answer: D

22. Rick up the incorrect statement

A. Lithium bromide used in vapour absorption cycle is non volatile

B. Lithium bromide plant can’t operate below 0°C

C. A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing

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

Answer: C

23. During dehumidification process, the relative humidity

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: C

24. The refrigerant widely used in domestic refrigerators is

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. R-12

Answer: D

25. The moisture in a refrigerant is removed by

A. Evaporator

B. Safety relief valve

C. Dehumidifier

D. Driers

Answer: D

26. During sensible cooling of air ________ decreases.

A. Wet bulb temperature

B. Relative humidity

C. Dry bulb temperature

D. Specific humidity

Answer: C

27. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant

A. Decreases

B. Increases

C. Remain same

D. Depends on other factors

Answer: B

28. The wet bulb depression is zero when relative humidity is

A. Zero

B. 0.5

C. 0.75

D. 1.0

Answer: D

29. The C.O.P of a refrigeration cycle with increase in evaporator temperature, keeping condenser temperature constant, will

A. Increase

B. Decrease

C. Remain unaffected

D. May increase or decrease depending on the type of refrigerant used

Answer: A

30. During humidification process, dry bulb temperature

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: A

31. The vapour pressure of refrigerant should be

A. Lower than atmospheric pressure

B. Higher than atmospheric pressure

C. Equal to atmospheric pressure

D. Could be anything

Answer: B

32. Which of the following statement is wrong?

A. The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.

B. In vapour compression cycle, the useful part of the heat transfer is at the condenser.

C. In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.

D. The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.

Answer: D

33. In a vapour compression system, the condition of refrigerant before passing through the condenser is

A. Saturated liquid

B. Wet vapour

C. Dry saturated vapour

D. Superheated vapour

Answer: D

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

A. Bigger cabinet should be used

B. Smaller cabinet should be used

C. Perfectly tight vapour seal should be used

D. Refrigerant with lower evaporation temperature should be used

Answer: C

35. During sensible heating of air _________ decreases.

A. Wet bulb temperature

B. Relative humidity

C. Dry bulb temperature

D. Specific humidity

Answer: B

36. One ton refrigeration corresponds to

A. 50 kcal/ min

B. 50 kcal/ hr

C. 80 kcal/ min

D. 80 kcal/ hr

Answer: A

37. The process, generally used in winter air-conditioning to warm and humidity the air, is called

A. Humidification

B. Dehumidification

C. Heating and humidification

D. Cooling and dehumidification

Answer: C

38. The leaks in a refrigeration system using Freon are detected by

A. Halide torch which on detection produces greenish flame lighting

B. Sulphur sticks which on detection gives white smoke

C. Using reagents

D. Smelling

Answer: A

39. The reduced ambient air cooling system has

A. One cooling turbine and one heat exchanger

B. One cooling turbine and two heat exchangers

C. Two cooling turbines and one heat exchanger

D. Two cooling turbines and two heat exchangers

Answer: C

40. In vapour compression cycle, the condition of refrigerant is saturated liquid

A. After passing through the condenser

B. Before passing through the condenser

C. After passing through the expansion throttle valve

D. Before entering the expansion valve

Answer: A

41. Which of the following refrigerant has the maximum ozone depletion potential in the stratosphere?

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. Fluorine

Answer: D

42. If the evaporator temperature of a plant is lowered, keeping the condenser temperature constant, the h.p. of compressor required will be

A. Same

B. More

C. Less

D. More/less depending on rating

Answer: B

43. Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.

A. Equalize

B. Reduce

C. Increase

D. None of these

Answer: C

44. Pick up the wrong statement. A refrigerant should have

A. Tow specific heat of liquid

B. High boiling point

C. High latent heat of vaporisation

D. Higher critical temperature

Answer: B

45. The pressure at the inlet of a refrigerant compressor is called

A. Suction pressure

B. Discharge pressure

C. Critical pressure

D. Back pressure

Answer: A

46. Condensing temperature in a refrigerator is the temperature

A. Of cooling medium

B. Of freezing zone

C. Of evaporator

D. At which refrigerant gas becomes liquid

Answer: D

47. In aircraft, air refrigeration Cycle is used because of

A. Low weight per tonne of refrigeration

B. High heat transfer rate

C. Low temperature at high altitudes

D. Higher coefficient of performance

Answer: A

48. Highest pressure encountered in a refrigeration system should be

A. Critical pressure of refrigerant

B. Much below critical pressure

C. Much above critical pressure

D. Near critical pressure

Answer: B

49. The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and

A. Carbon dioxide

B. Sulphur dioxide

C. Lithium bromide

D. R-12

Answer: C

50. One ton of the refrigeration is

A. The standard unit used in refrigeration problems

B. The cooling effect produced by melting 1 ton of ice

C. The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

D. The refrigeration effect to produce 1 ton of ice at NTP conditions

Answer: C

51. The dry bulb temperature during sensible heating of air

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: B

52. Vertical lines on pressure-enthalpy chart show constant

A. Pressure lines

B. Temperature lines

C. Total heat lines

D. Entropy lines

Answer: C

53. During heating and dehumidification process, dry bulb temperature

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: B

54. The evolution of heat of solution takes place in ammonia absorption plant when

A. Ammonia vapour goes into solution

B. Ammonia vapour is driven out of solution

C. Lithium bromide mixes with ammonia

D. Weak solution mixes with strong solution

Answer: A

55. In a pressure enthalpy chart, the space to the left of the saturated liquid line represents

A. Wet vapour region

B. Superheated vapour region

C. Sub-cooled liquid region

D. None of these

Answer: C

56. In vapour compression cycle, the condition of refrigerant is high pressure saturated liquid

A. After passing through the condenser

B. Before passing through the condenser

C. After passing through the expansion or throttle valve

D. Before entering the expansion valve

Answer: D

57. In a bootstrap air evaporative cooling system, the evaporator is provided

A. Between the combustion chamber and the first heat exchanger

B. Between the first heat exchanger and the secondary compressor

C. Between the secondary compressor and the second heat exchanger

D. Between the second heat exchanger and the cooling turbine

Answer: D

58. The COP of a domestic refrigerator

A. Is less than 1

B. Is more than 1

C. Is equal to 1

D. Depends upon the make

Answer: B

59. The air cooling system mostly used in transport type aircrafts is

A. Simple air cooling system

B. Simple evaporative air cooling system

C. Bootstrap air cooling system

D. All of these

Answer: C

60. The higher temperature in vapour compression cycle occurs at

A. Receiver

B. Expansion valve

C. Evaporator

D. Compressor discharge

Answer: D

61. Dry bulb temperature is the temperature of air recorded by a thermometer, when

A. It is not affected by the moisture present in the air

B. Its bulb is surrounded by a wet cloth exposed to the air

C. The moisture present in it begins to condense

D. None of the above

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

A. High, of the order of 25°

B. As low as possible (3 to 11°C)

C. Zero

D. Any value

Answer: B

63. The evaporator changes the low pressure liquid refrigerant from the expansion valve into

A. High pressure liquid refrigerant

B. Low pressure liquid and vapour refrigerant

C. Low pressure vapour refrigerant

D. None of these

Answer: C

64. Choose the correct statement

A. A refrigerant should have low latent heat

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

C. Pre-cooling and sub-cooling bf refrigerant are same

D. Superheat and sensible heat of a refrigerant are same

Answer: B

65. Carbon dioxide is

A. Colourless

B. Odourless

C. Non-flammable

D. All of these

Answer: D

66. Reducing suction pressure in refrigeration cycle

A. Lowers evaporation temperature

B. Increases power required per ton of refrigeration

C. Lowers compressor capacity because vapour is lighter

D. All of the above

Answer: D

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

A. Same

B. Less

C. More

D. None of these

Answer: B

68. If a gas is to be liquefied, its temperature must be

A. Increased to a value above its critical temperature

B. Reduced to a value below its critical temperature

C. Equal to critical temperature

D. None of the above

Answer: C

69. The capacity of a domestic refrigerator is in the range of

A. 0.1 to 0.3 TR

B. 1 to 3 TR

C. 3 to 5 TR

D. 5 to 7 TR

Answer: A

70. The lowest thermal diffusivity is of

A. Iron

B. Lead

C. Aluminium

D. Rubber

Answer: D

71. In a vapour compression cycle, the refrigerant immediately after expansion valve is

A. Liquid

B. Sub-cooled liquid

C. Saturated liquid

D. Wet vapour

Answer: D

72. Which of the following statement is correct for ammonia as a refrigerant?

A. It is toxic to mucous membranes.

B. It requires large displacement per TR compared to fluoro carbons.

C. It reacts with copper and its alloys.

D. All of these

Answer: D

73. Critical pressure of a liquid is the pressure

A. Above which liquid will remain liquid

B. Above which liquid becomes gas

C. Above which liquid becomes vapour

D. Above which liquid becomes solid

Answer: A

74. The optimum effective temperature for human comfort is

A. Higher in winter than in summer

B. Lower in winter than in summer

C. Same in winter and summer

D. Not dependent on season

Answer: B

75. Formation of frost on evaporator in refrigerator

A. Results in loss of heat due to poor heat transfer

B. Increases heat transfer rate

C. Is immaterial

D. Can be avoided by proper design

Answer: A

76. A one tonne refrigerating machine means that

A. One tonne is the total mass of machine

B. One tonne refrigerant is used

C. One tonne of water can be converted into ice

D. One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

Answer: D

77. The suction pipe diameter of refrigerating unit compressor in comparison to delivery side is

A. Bigger

B. Smaller

C. Equal

D. Smaller/bigger depending on capacity

Answer: A

78. 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

Answer: B

79. Presence of moisture in a refrigerant affects the working of

A. Compressor

B. Condenser

C. Evaporator

D. Expansion valve

Answer: D

80. During heating and humidification, the final relative humidity of air

A. Can be lower or higher than that of the entering air

B. Is lower than that of the entering air

C. Is higher than that of the entering air

D. None of the above

Answer: A

81. Which of the following cycles uses air as the refrigerant?

A. Ericson

B. Stirling

C. Carnot

D. Bell Coleman

Answer: D

82. The curved lines on a psychrometric chart indicates

A. Dry bulb temperature

B. Wet bulb temperature

C. Dew point temperature

D. Relative humidity

Answer: D

83. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

A. Involves no change in volume

B. Takes place at constant temperature

C. Takes place at constant entropy

D. Takes place at constant pressure

Answer: D

84. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

A. Positive

B. Negative

C. Zero

D. None of these

Answer: B

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

A. 0.1 to 0.5 h.p. per ton of refrigeration

B. 0.5 to 0.8 h.p. per ton of refrigeration

C. 1 to 2 h.p. per ton of refrigeration

D. 2 to 5 h.p. per ton of refrigeration

Answer: C

86. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

A. 0.376

B. 0.4

C. 0.6

D. 0.67

Answer: C

87. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

A. More

B. Less

C. Equally

D. Unpredictable

Answer: A

88. Most thermostatic expansion valves are set for a superheat of

A. 5°C

B. 10°C

C. 15°C

D. 20°C

Answer: A

89. In a refrigeration system, heat absorbed in comparison to heat rejected is

A. More

B. Less

C. Same

D. More for small capacity and less for high capacity

Answer: B

90. A thermostatic expansion valve in a refrigeration system

A. Ensures the evaporator completely filled with refrigerant of the load

B. Is suitable only for constant load systems

C. Maintains different temperatures in evaporator in proportion to load

D. None of the above

Answer: A

91. Freon group of refrigerants are

A. Inflammable

B. Toxic

C. Non-inflammable and toxic

D. Nontoxic and non-inflammable

Answer: D

92. The boiling point of ammonia is

A. -10.5°C

B. -30°C

C. -33.3°C

D. -77.7°C

Answer: C

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

A. High

B. Low

C. Optimum

D. Any value

Answer: B

94. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

A. 1.33

B. 2.33

C. 3.33

D. 4.33

Answer: B

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

A. Condenser

B. Evaporator

C. Absorber

D. Condenser, absorber and separator (rectifier)

Answer: D

96. The freezing point of sulphur dioxide is

A. -56.6°C

B. -75.2°C

C. -77.7°C

D. -135.8°C

Answer: B

97. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

A. 1: 1

B. 1: 9

C. 9: 1

D. 1: 3

Answer: B

98. In a refrigeration system, the expansion device is connected between the

A. Compressor and condenser

B. Condenser and receiver

C. Receiver and evaporator

D. Evaporator and compressor

Answer: C

99. The vapour compression refrigerator employs the following cycle

A. Rankine

B. Carnot

C. Reversed Rankine

D. Reversed Carnot

Answer: D

100. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

A. 1

B. 1.25

C. 2.15

D. 5.12

Answer: B

101. Rating of a domestic refrigerator is of the order of

A. 0.1 ton

B. 5 tons

C. 10 tons

D. 40 tons

Answer: A

102. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

A. Heat dissipated to the surroundings

B. Heat stored in the human body

C. Sum ofA. andB.

D. Difference ofA. andB.

Answer: C

103. The bank of tubes at the back of domestic refrigerator is

A. Condenser tubes

B. Evaporator tubes

C. Refrigerant cooling tubes

D. Capillary tubes

Answer: A

104. In a lithium bromide absorption refrigeration system

A. Lithium bromide is used as a refrigerant and water as an absorbent

B. Water is used as a refrigerant and lithium bromide as an absorbent

C. Ammonia is used as a refrigerant and lithium bromide as an absorbent

D. None of the above

Answer: B

105. The condition of refrigerant after passing through the condenser in a vapour compression system is

A. Saturated liquid

B. Wet vapour

C. Dry saturated vapour

D. Superheated vapour

Answer: A

106. The value of C.O.P in vapour compression cycle is usually

A. Always less than unity

B. Always more than unity

C. Equal to unity

D. Any one of the above

Answer: B

107. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

A. T₁ / (T₂ – T₁)

B. (T₂ – T₁)/T₁

C. (T₁ – T₂)/T₁

D. T₂/ (T₂ – T₁)

Answer: A

108. Which of the following is not a desirable property of a refrigerant?

A. High risibility with oil

B. Low boiling point

C. Good electrical conductor

D. Large latent heat

Answer: C

109. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

A. Sub-cooling or under-cooling

B. Super-cooling

C. Normal cooling

D. None of these

Answer: A

110. 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

A. Ammonia

B. Carbon dioxide

C. Freon

D. Brine

Answer: B

111. The capillary tube, as an expansion device, is used in

A. Domestic refrigerators

B. Water coolers

C. Room air conditioners

D. All of these

Answer: D

112. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

A. 0.2

B. 1.2

C. 5

D. 6

Answer: D

113. Which of the following statement is correct?

A. The human body can lose heat even if its temperature is less than the atmospheric temperature.

B. The increase in air movement increases the evaporation from the human body.

C. The warm air increases the rate of radiation of heat from the human body.

D. BothA. andB.

Answer: D

114. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

A. Collect liquid refrigerant and prevent it from going to compressor

B. Detect liquid in vapour

C. Superheat the vapour

D. Collect vapours

Answer: A

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

A. Dew point temperature of air

B. Wet bulb temperature of air

C. Dry bulb temperature of air

D. Ambient air temperature

Answer: B

116. Highest temperature encountered in refrigeration cycle should be

A. Near critical temperature of refrigerant

B. Above critical temperature

C. At critical Temperature

D. Much below critical temperature

Answer: D

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

A. 2 bar

B. 8 bar

C. 15 bar

D. 30 bar

Answer: B

118. The domestic refrigerator uses following type of compressor

A. Centrifugal

B. Axial

C. Miniature sealed unit

D. Piston type reciprocating

Answer: D

119. A bootstrap air cooling system has

A. One heat exchanger

B. Two heat exchangers

C. Three heat exchangers

D. Four heat exchangers

Answer: B

120. Critical temperature is the temperature above which

A. A gas will never liquefy

B. A gas will immediately liquefy

C. Water will evaporate

D. Water will never evaporate

Answer: A

121. Which of the following statement is correct?

A. The constant enthalpy lines are also constant wet bulb temperature lines

B. The wet bulb and dry bulb temperature are equal at saturation condition

C. The wet bulb temperature is a measure of enthalpy of moist air

D. All of the above

Answer: D

122. In vapour compression cycle, the condition of refrigerant is very wet vapour

A. After passing through the condenser

B. Before passing through the condenser

C. After passing through the expansion or throttle valve

D. Before entering the compressor

Answer: D

123. During cooling and dehumidification, dry bulb temperature

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: C

124. Ammonia absorption refrigeration cycle requires

A. Very little work input

B. Maximum work input

C. Nearly same work input as for vapour compression cycle

D. Zero work input

Answer: A

125. Which of the following refrigerant has the highest freezing point.

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. R-12

Answer: B

126. A standard ice point temperature corresponds to the temperature of

A. Water at 0°C

B. Ice at 4°C

C. Solid and dry ice

D. Mixture of ice and water under equilibrium conditions

Answer: D

127. The sub-cooling in a refrigeration cycle

A. Does not alter C.O.P.

B. Increases C.O.P.

C. Decreases C.O.P.

D. None of these

Answer: B

128. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,

A. Will be higher

B. Will be lower

C. Will remain unaffected

D. May be higher or lower depending upon the nature of non-condensable gases

Answer: A

129. The Freon group of refrigerants are

A. Halocarbon refrigerants

B. Zoetrope refrigerants

C. Inorganic refrigerants

D. Hydrocarbon refrigerants

Answer: A

130. For better C.O.P of refrigerator, the pressure range corresponding to temperature in evaporator and condenser must be

A. Small

B. High

C. Equal

D. Anything

Answer: A

131. In vapour compression refrigeration system, refrigerant occurs as liquid between

A. Condenser and expansion valve

B. Compressor and evaporator

C. Expansion valve and evaporator

D. Compressor and condenser

Answer: C

132. The wet bulb depression indicates _________ humidity of the air.

A. Absolute

B. Relative

C. Specific

D. None of these

Answer: B

133. The sensible heat factor during the heating and humidification process is given by (where h₁ = Enthalpy of air entering the heating coil, h₂ = Enthalpy of air leaving the heating coil, and hA = Enthalpy of air at the end of humidification process)

A. (hA – h2)/ (h1 – h2)

B. (h2 – hA)/ (h1 – h2)

C. (h1 – h2)/ (hA – h2)

D. (hA – h1)/ (h2 – h1)

Answer: D

134. The lower horizontal line of the refrigeration cycle plotted on pressure-enthalpy diagram represents

A. Condensation of the refrigerant vapour

B. Evaporation of the refrigerant liquid

C. Compression of the refrigerant vapour

D. Metering of the refrigerant liquid

Answer: B

135. The leakage in a refrigeration system using Freon is detected by

A. Halide torch

B. Sulphur sticks

C. Soap and water

D. All of these

Answer: A

136. The conditioned air supplied to the room must have the capacity to take up

A. Room sensible heat load only

B. Room latent heat load only

C. Both room sensible heat and latent heat loads

D. None of the above

Answer: C

137. Moisture in Freon refrigeration system causes

A. Ineffective refrigeration

B. High power consumption

C. Freezing automatic regulating valve

D. Corrosion of whole system

Answer: C

138. The boiling point of ________ is 10.5°C.

A. Ammonia

B. R-12

C. Sulphur dioxide

D. Carbon dioxide

Answer: C

139. The refrigeration effect in a dry evaporator compared to flooded evaporator in a similar plant is

A. Same

B. More

C. Less

D. More or less depending on ambient conditions

Answer: C

140. The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as

A. Mean radiant temperature

B. Effective temperature

C. Dew point temperature

D. None of these

Answer: B

141. Which of the following refrigerants has lowest freezing point?

A. Freon-12

B. NH3

C. CO2

D. Freon-22

Answer: D

142. The thermostatic expansion valve is used in ________ type of evaporators.

A. Flooded

B. DX coil

C. Dry

D. None of these

Answer: C

143. The boiling point of ammonia is

A. 100°C

B. 50°C

C. 33.3°C

D. 0°C

Answer: C

144. The specific humidity during heating and humidification process.

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: B

145. The relative coefficient of performance is

A. Actual COP/theoretical COP

B. Theoretical COP/actual COP

C. Actual COP × theoretical COP

D. None of these

Answer: A

146. The wet bulb temperature at 100% relative humidity is ________ dew point temperature.

A. Same as

B. Lower than

C. Higher than

D. None of these

Answer: A

147. Vapour compression refrigeration is somewhat like

A. Carnot cycle

B. Rankine’s cycle

C. Reversed Carnot cycle

D. None of the above

Answer: D

148. A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be

A. 1 kW

B. 2 kW

C. 3 kW

D. 4 kW

Answer: D

149. Aqua ammonia is used as refrigerant in the following type of refrigeration system

A. Compression

B. Direct

C. Indirect

D. Absorption

Answer: D

150. Air conditioning means

A. Cooling

B. Heating

C. Dehumidifying

D. All of these

Answer: D

151. The advantage of dry compression is that

A. It permits higher speeds to be used

B. It permits complete evaporation in the evaporator

C. It results in high volumetric and mechanical efficiency

D. All of the above

Answer: D

152. The specific humidity during dehumidification process

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: C

153. The C.O.P. of a refrigeration cycle with lowering of condenser temperature, keeping the evaporator temperature constant, will

A. Increase

B. Decrease

C. May increase or decrease depending on the type of refrigerant used

D. Remain unaffected

Answer: A

154. The alignment circle is marked on the psychrometric chart at

A. 20°C DBT and 50% RH

B. 26°C DBT and 50% RH

C. 20°C DBT and 60% RH

D. 26°C DBT and 60% RH

Answer: B

155. 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

A. 0.2

B. 1.2

C. 5

D. 6

Answer: C

156. Relative humidity is given by (where pv = Partial pressure of water vapour, pb = Barometric pressure, ps = Pressure of saturated air, pd = Pressure at dry bulb temperature, pw = Saturation pressure corresponding to wet bulb temperature, and μ = Degree of saturation)

A. 0.622 Pv / (Pb – Pv)

B. μ/[1 – (1 – μ) (Ps/Pb)]

C. [Pv (Pb – Pd)]/ [Pd (Pb – Pv)]

D. None of these

Answer: B

157. In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is

A. Less than 2 kg

B. More than or equal to 3.65 kg

C. More than 10 kg

D. There is no such consideration

Answer: B

158. During sensible cooling,

A. Relative humidity remains constant

B. Wet bulb temperature increases

C. Specific humidity increases

D. Partial pressure of vapour remains constant

Answer: D

159. Choose the wrong statement

A. Temperature of medium being cooled must be below that of the evaporator

B. Refrigerant leaves the condenser as liquid

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

D. Frost on evaporator reduces heat transfer

Answer: A

160. The superheating in a refrigeration cycle

A. Does not alter C.O.P.

B. Increases C.O.P.

C. Decreases C.O.P.

D. None of these

Answer: C

161. Refrigeration in aeroplanes usually employs the following refrigerant

A. CO2

B. Freon-11

C. Freon-22

D. Air

Answer: D

162. The condition of refrigerant as it leaves the compressor in a vapour compression system is

A. Saturated liquid

B. Wet vapour

C. Dry saturated vapour

D. Superheated vapour

Answer: D

163. The coefficient of performance is the ratio of the refrigerant effect to the

A. Heat of compression

B. Work done by compressor

C. Enthalpy increase in compressor

D. All of the above

Answer: D

164. 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)

Answer: B

165. Air refrigeration operates on

A. Carnot cycle

B. Reversed Carnot cycle

C. Rankine’s cycle

D. Brayton cycle

Answer: D

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

A. Which lies between the dry bulb and wet bulb temperatures of the incoming stream

B. Which lies between the wet bulb and dew point temperatures of the incoming stream

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

D. Of adiabatic saturation of incoming stream

Answer: C

167. Superheating in a refrigeration cycle

A. Increases C.O.P

B. Decreases C.O.P

C. C.O.P remains unaltered

D. Other factors decide C.O.P

Answer: B

168. The specific humidity during cooling and dehumidification

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: C

169. Chaperon equation is applicable for registration at

A. Saturation point of vapour

B. Saturation point of liquid

C. Sublimation temperature

D. Triple point

Answer: A

170. For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of

A. Copper

B. Aluminium

C. Steel

D. Brass

Answer: C

171. The refrigerant for a refrigerator should have

A. High sensible heat

B. High total heat

C. High latent heat

D. Low latent heat

Answer: C

172. The bypass factor for a cooling coil

A. Increases with increase in velocity of air passing through it

B. Decreases with increase in velocity of air passing through it

C. Remains unchanged with increase in velocity of air passing through it

D. May increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

Answer: A

173. Accumulators should have adequate volume to store refrigerant charge at least

A. 10%

B. 25%

C. 50%

D. 75%

Answer: C

174. The dry bulb temperature lines, on the psychrometric chart are

A. Vertical and uniformly spaced

B. Horizontal and uniformly spaced

C. Horizontal and non-uniformly spaced

D. Curved lines

Answer: A

175. In S.J. unit, one ton of refrigeration is equal to

A. 210 kJ/ min

B. 21 kJ/ min

C. 420 kJ/ min

D. 840 kJ/ min

Answer: A

176. The cooling system used for supersonic aircrafts and rockets is

A. Simple air cooling system

B. Bootstrap air cooling system

C. Reduced ambient air cooling system

D. Regenerative air cooling system

Answer: D

177. Short horizontal lines on pressure-enthalpy chart show

A. Constant pressure lines

B. Constant temperature lines

C. Constant total heat lines

D. Constant entropy lines

Answer: A

178. Which of the following statement is wrong?

A. The value of C.O.P. is always greater than one

B. In a vapour compression system, the condition of refrigerant before entering the compressor is dry saturated vapour

C. The space between the saturated liquid line and saturated vapour line, in a pressure enthalpy chart, is wet vapour region

D. None of the above

Answer: D

179. One ton of refrigeration is equal to the refrigeration effect corresponding to melting of 1000 kg of ice

A. In 1 hour

B. In 1 minute

C. In 24 hours

D. In 12 hours

Answer: C

180. In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by

A. Liquid pump

B. Generator

C. Absorber and generator

D. Absorber, generator and liquid pump

Answer: D

181. Efficiency of a Carnot engine is given as 80%. If the cycle direction be reversed, what will be the value of C.O.P. of reversed Carnot Cycle?

A. 1.25

B. 0.8

C. 0.5

D. 0.25

Answer: D

182. The refrigerant supplied to a compressor must be

A. Superheated vapour refrigerant

B. Dry saturated liquid refrigerant

C. A mixture of liquid and vapour refrigerant

D. None of these

Answer: A

183. One of the purposes of sub cooling the liquid refrigerant is to

A. Reduce compressor overheating

B. Reduce compressor discharge temperature

C. Increase cooling effect

D. Ensure that only liquid and not the vapour enters the expansion (throttling) valve

Answer: D

184. The ratio of heat extracted in the refrigerator to the work-done on the refrigerant is called

A. Coefficient of performance of refrigeration

B. Coefficient of performance of heat pump

C. Relative coefficient of performance

D. Refrigerating efficiency

Answer: A

185. In vapour compression cycle the condition off refrigerant is dry saturated vapour

A. After passing through the condenser

B. Before passing through the condenser

C. After passing through the expansion or throttle valve

D. Before entering the compressor

Answer: D

186. In larger industrial and commercial reciprocating compression systems, refrigerant widely used is

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. R-12

Answer: A

187. In vapour compression cycle the condition of refrigerant is superheated vapour

A. After passing through the condenser

B. Before passing through the condenser

C. After passing through the expansion or throttle valve

D. Before entering the expansion valve

Answer: B

188. In which of the following refrigeration system, waste heat can be effectively used?

A. Vapour compression cycle

B. Vapour absorption cycle

C. Air refrigeration cycle

D. None of these

Answer: B

189. Pick up the correct statement about giving up of heat from one medium to other in ammonia absorption system

A. Strong solution to weak solution

B. Weak solution to strong solution

C. Strong solution to ammonia vapour

D. Ammonia vapours to weak solution

Answer: B

190. The material of pipe lines for a system using Freon as a refrigerant should be

A. Brass

B. Copper

C. Steel

D. Aluminium

Answer: B

191. Ammonia is

A. Non-toxic

B. Non-inflammable

C. Toxic and non-inflammable

D. Highly toxic and inflammable

Answer: D

192. The sensible heat factor during cooling and dehumidification process is given by (where h₁ = Enthalpy of air entering the cooling coil, h₂ = Enthalpy of air leaving the cooling coil, and hA = Enthalpy of air at the end of dehumidification process)

A. (hA – h2)/ (h1 – h2)

B. (h2 – hA)/ (h1 – h2)

C. (h1 – h2)/ (hA – h2)

D. (hA – h1)/ (h2 – h1)

Answer: A

193. Most of the domestic refrigerators work on the following refrigeration system

A. Vapour compression

B. Vapour absorption

C. Carnot cycle

D. Electrolux refrigerator

Answer: A

194. For unsaturated air, the dew point temperature is __________ wet bulb temperature.

A. Equal to

B. Less than

C. More than

D. None of these

Answer: B

195. Air refrigeration cycle is used in

A. Domestic refrigerators

B. Commercial refrigerators

C. Air conditioning

D. Gas liquefaction

Answer: D

196. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

A. Wet bulb temperature

B. Dry bulb temperature

C. Dew point temperature

D. None of these

Answer: A

197. The C.O.P. of an absorption type refrigerator is given by (where T₁ = Temperature at which the working substance receives heat, T₂ = Temperature of cooling water, and T₃ = Evaporator temperature)

A. [T₁ (T₂ – T₃)] / [T₃ (T₁ – T₂)]

B. [T₃ (T₁ – T₂)]/ [T₁ (T₂ – T₃)]

C. [T₁ (T₁ – T₂)] / [T₃ (T₂ – T₃)]

D. [T₃ (T₂ – T₃)] / [T₁ (T₁ – T₂)]

Answer: B

198. The humidity ratio or specific humidity is the mass of water vapour present in

A. 1 m3 of wet air

B. 1 m3 of dry air

C. 1 kg of wet air

D. 1 kg of dry air

Answer: D

199. During adiabatic saturation process on unsaturated air __________ remains constant.

A. Relative humidity

B. Dew point temperature

C. Dry bulb temperature

D. Wet bulb temperature

Answer: D

200. Degree of saturation or percentage humidity is

A. The mass of water vapour present in 1 m³ of dry air

B. The mass of water vapour present in 1 kg of dry air

C. The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure

D. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

Answer: C

201. The reciprocating refrigerant compressors are very suitable for

A. Small displacements and low condensing pressures

B. Large displacements and high condensing pressures

C. Small displacements and high condensing pressures

D. Large displacements and low condensing pressures

Answer: C

202. The desirable property of a refrigerant is

A. Low boiling point

B. High critical temperature

C. High latent heat of vaporisation

D. All of these

Answer: D

203. The humidification process, on the psychrometric chart is shown by

A. Horizontal line

B. Vertical line

C. Inclined line

D. Curved line

Answer: B

204. The evaporator used in household refrigerators is

A. Frosting evaporator

B. Non-frosting evaporator

C. Defrosting evaporator

D. None of these

Answer: A

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

A. B.P.F. – 1

B. 1 – B. P.F.

C. 1/ B.P.F.

D. 1 + B.P.F.

Answer: B

206. In a refrigerating machine, heat rejected is _________ heat absorbed.

A. Equal to

B. Less than

C. Greater than

D. None of these

Answer: C

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

A. Water and water

B. Water and lithium bromide

C. Ammonia and lithium bromide

D. Ammonia and water

Answer: D

208. In air-conditioning of aeroplanes, using air as a refrigerant, the cycle used is

A. Reversed Carnot cycle

B. Reversed Joule cycle

C. Reversed Brayton cycle

D. Reversed Otto cycle

Answer: C

209. The mass of water vapour present in __________ is called absolute humidity.

A. 1 m3 of water

B. 1 m3 of dry air

C. 1 kg of wet air

D. 1 kg of dry air

Answer: B

210. While designing the refrigeration system of an aircraft, the prime consideration is that the

A. System has high C.O.P.

B. Power per TR is low

C. Mass of refrigerant circulated in the system is low

D. Mass of the refrigeration equipment is low

Answer: D

211. The formation of frost on cooling coils in a refrigerator

A. Increases heat transfer

B. Improves C.O.P. of the system

C. Increases power consumption

D. Reduces power consumption

Answer: C

212. The power per tonne of refrigeration is

A. 3.5/C.O.P.

B. C.O.P/3.5

C. 3.5 × C.O.P.

D. None of these

Answer: A

213. The wet bulb temperature during sensible heating of air

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: B

214. The relative humidity is defined as

A. The mass of water vapour present in 1 m3 of dry air

B. The mass of water vapour present in 1 kg of dry air

C. The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure

D. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

Answer: D

215. As relative humidity decreases, the dew point temperature will be ________ wet bulb temperature.

A. Same as

B. Lower than

C. Higher than

D. None of these

Answer: B

216. In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be

A. 0.3

B. 0.6

C. 0.67

D. 1.5

Answer: B

217. An Electrolux refrigerator is called a _________ absorption system.

A. Single fluid

B. Two fluids

C. Three fluids

D. None of these

Answer: C

218. It is desired to condition the outside air from 70% relative humidity and 45° C dry bulb temperature to 50% relative humidity and 25° C dry bulb temperature (room condition). The practical arrangement will be

A. Dehumidification

B. Cooling and humidification

C. Cooling and dehumidification

D. Dehumidification and pure sensible cooling

Answer: C

219. The difference between dry bulb temperature and wet bulb temperature, is called

A. Dry bulb depression

B. Wet bulb depression

C. Dew point depression

D. Degree of saturation

Answer: B

220. The coefficient of performance of Heat Pump is always _________ one.

A. Equal to

B. Less than

C. Greater than

D. None of these

Answer: C

221. An evaporator is also known as

A. Freezing coil

B. Cooling coil

C. Chilling coil

D. All of these

Answer: D

222. A refrigeration system

A. Removes heat from a low temperature body and delivers it to a high temperature body

B. Removes heat from a high temperature body and delivers it to a low temperature body

C. Rejects energy to a low temperature body

D. None of the above

Answer: A

223. Nusselt number (NN) is given by

A. NN = hl/k

B. NN = μ cp/k

C. NN = ρ V l /μ

D. NN = V²/t.cp

Answer: A

224. The temperature of ammonia after compression in a vapour compression system is

A. 20 to 50°C

B. 50 to 70°C

C. 70 to 110°C

D. None of these

Answer: C

225. A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be

A. Lack of cooling water

B. Water temperature being high

C. Dirty condenser surface

D. All of these

Answer: D

226. For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference ™ for parallel flow is ________ that for counter flow.

A. Equal to

B. Less than

C. Greater than

D. None of these

Answer: A

227. A vapour absorption refrigerator uses _________ as a refrigerant.

A. Water

B. Ammonia

C. Freon

D. Aqua-ammonia

Answer: D

228. Bell Coleman cycle is a

A. Reversed Carnot cycle

B. Reversed Otto cycle

C. Reversed Joule cycle

D. Reversed Rankine cycle

Answer: C

229. The coefficient of performance of Electrolux refrigerator is the ratio of

A. Heat supplied by the gas burner to the heat absorbed by the evaporator

B. Heat absorbed by the evaporator to the heat supplied by the gas burner

C. Heat supplied by the gas burner minus the heat absorbed by the evaporator to the heat supplied by the gas burner

D. Heat absorbed by the evaporator minus the heat supplied by the gas burner to the heat absorbed by the evaporator

Answer: B

230. Which of the following refrigerant has the lowest freezing point?

A. R-11

B. R-12

C. R-22

D. Ammonia

Answer: C

231. In Electrolux refrigerator

A. Ammonia is absorbed in hydrogen

B. Ammonia is absorbed in water

C. Ammonia evaporates in hydrogen

D. Hydrogen evaporates in ammonia

Answer: C

232. One tonne of refrigeration (1TR) means that the heat removing capacity is

A. 21 kJ/min

B. 210 kJ/min

C. 420 kJ/min

D. 620 kJ/min

Answer: B

233. The superheated vapour region, in a pressure enthalpy chart, is represented by the space

A. To the left of saturated liquid line

B. To the right of saturated liquid line

C. Between the saturated liquid line and saturated vapour line

D. None of the above

Answer: C

234. A good refrigerant should have

A. High latent heat of vaporisation and low freezing point

B. High operating pressures and low freezing point

C. High specific volume and high latent heat of vaporisation

D. Low C.O.P. and low freezing point

Answer: A

235. Air refrigeration cycle is used in

A. Commercial refrigerators

B. Domestic refrigerators

C. Air-conditioning

D. Gas liquefaction

Answer: D

236. In a saturated air-water vapour mixture, the

A. Dry bulb temperature is higher than wet bulb temperature

B. Dew point temperature is lower than wet bulb temperature

C. Dry bulb, wet bulb and dew point temperature are same

D. Dry bulb temperature is higher than dew point temperature

Answer: C

237. The capillary tube is not used in large capacity refrigeration systems because

A. Cost is too high

B. Capacity control is not possible

C. It is made of copper

D. Required pressure drop cannot be achieved

Answer: B

238. The thermostatic expansion valve operates on the changes in the

A. Degree of superheat at exit from the evaporator

B. Temperature of the evaporator

C. Pressure in the evaporator

D. None of the above

Answer: A

239. In a vapour compression system, the condition of refrigerant before entering the expansion or throttle valve is

A. High pressure saturated liquid

B. Wet vapour

C. Very wet vapour

D. Dry vapour

Answer: A

240. The freezing point of R-12 is

A. -86.6°C

B. -95.2°C

C. -107.7°C

D. -135.8°C

Answer: D

241. The unit of thermal diffusivity is

A. m/hK

B. m/h

C. m²/h

D. m²/hK

Answer: C

242. The comfort conditions in air conditioning are at (where DBT = Dry bulb temperature, and RH = Relative humidity)

A. 25°C DBT and 100% RH

B. 20°C DBT and 80% RH

C. 22°C DBT and 60% RH

D. 25°C DBT and 40% RH

Answer: C

243. The pressure at the outlet of a refrigerant compressor is called

A. Suction pressure

B. Discharge pressure

C. Critical pressure

D. Back pressure

Answer: B

244. The bypass factor, in case of sensible cooling of air, is given by (where td₁ = Dry bulb temperature of air entering the cooling coil, td₂ = Dry bulb temperature of air leaving the cooling coil, and td₃ = Dry bulb temperature of the cooling coil)

A. (td₁ -td₃)/( td₂ -td₃)

B. (td₂ -td₃)/( td₁ -td₃)

C. (td₃ -td₁)/( td₂ -td₃)

D. (td₃ -td₂)/( td₁ -td₃)

Answer: B

245. The operating temperature of a cold storage is 2°C. The heat leakage from the surrounding is 30 kW for the ambient temperature of 40°C. The actual C.O.P. of refrigeration plant used is one fourth that of ideal plant working between the same temperatures. The power required to drive the plant is

A. 1.86 kW

B. 3.72 kW

C. 7.44 kW

D. 18.6 kW

Answer: D

246. In chemical dehumidification process,

A. Dew point temperature decreases

B. Wet bulb temperature decreases

C. Dry bulb temperature increases

D. All of these

Answer: D

247. Environmental protection agencies advice against the use of chlorofluorocarbon refrigerants since

A. These react with water vapour and cause acid rain

B. These react with plants and cause greenhouse effect

C. These react with oxygen and cause its depletion

D. These react with ozone layer

Answer: D

248. When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by

A. Operating the machine at higher speeds

B. Operating the machine at lower speeds

C. Raising the higher temperature

D. Lowering the higher temperature

Answer: D

249. The bypass factor of a cooling coil decreases with

A. Decrease in fin spacing and increase in number of rows

B. Increase in fin spacing and increase in number of rows

C. Increase in fin spacing and decrease in number of rows

D. Decrease in fin spacing and decrease in number of rows

Answer: A

250. A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called

A. Dry air

B. Moist air

C. Saturated air

D. Specific humidity

Answer: C

251. The total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called

A. Kinetic theory of gases

B. Newton’s law of gases

C. Dalton’s law of partial pressures

D. Avogadro’s hypothesis

Answer: C

252. The relative humidity lines on a psychrometric chart are

A. Vertical and uniformly spaced

B. Horizontal and uniformly spaced

C. Horizontal and non-uniformly spaced

D. Curved lines

Answer: D

253. The C.O.P. of a heat pump working on a reversed Carnot cycle is

A. T₁/(T₂ – T₁)

B. (T₂ – T₁)/T₁

C. (T₁ – T₂)/T₁

D. T₂/(T₂ – T₁)

Answer: D

254. A vapour absorption refrigeration system

A. Gives noisy operation

B. Gives quiet operation

C. Requires little power consumption

D. Cools below 0°C

Answer: B

255. A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300 K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with Cp = 1 kJ/kg)

A. 25 kJ/kg

B. 50 kJ/kg

C. 100 kJ/kg

D. 125 kJ/kg

Answer: B

256. The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure, is called

A. Humidity ratio

B. Relative humidity

C. Absolute humidity

D. Degree of saturation

Answer: D

257. During dehumidification process, _________ remains constant.

A. Wet bulb temperature

B. Relative humidity

C. Dry bulb temperature

D. Specific humidity

Answer: C

258. Pressure of water vapour is given by

A. 0.622 Pv/ (Pb – Pv)

B. μ/[1 – (1 – μ) (Ps/Pb)]

C. [Pv (Pb – Pd)]/ [Pd (Pb – Pv)]

D. None of these

Answer: D

259. R-12 is generally preferred over R-22 in deep freezers since

A. It has low operating pressures

B. It gives higher coefficient of performance

C. It is miscible with oil over large range of temperatures

D. All of the above

Answer: C

260. In a spray washing system, if the temperature of water is higher than the dry bulb temperature of entering air, then the air is

A. Heated and dehumidified

B. Heated and humidified

C. Cooled and humidified

D. Cooled and dehumidified

Answer: B

261. A valve which maintains a constant degree of superheat at the end of the evaporator coil, is called

A. Automatic expansion valve

B. High side float valve

C. Thermostatic expansion valve

D. Low side float valve

Answer: D

262. An infinite parallel planes with emissivities e₁ and e₂, the interchange factor for radiation from surface 1 to surface 2 is given by

A. (e₁ + e₂)/ e₁ + e₂ – e₁e₂

B. 1/e₁ + 1/e₂

C. e₁ + e₂

D. e₁e₂

Answer: A

263. The emissivity of a polished silver body is _________ as compared to black body.

A. Same

B. Low

C. Very low

D. High

Answer: C

264. Air refrigerator works on

A. Reversed Carnot cycle

B. Bell Coleman cycle

C. BothA. andB.

D. None of these

Answer: C

265. The relative coefficient of performance is equal to

A. (Theoretical C.O.P.)/ (Actual C.O.P.)

B. (Actual C.O.P.) /(Theoretical C.O.P.)

C. (Actual C.O.P.) × (Theoretical C.O.P.)

D. None of these

Answer: B

266. In case of sensible cooling of air, the coil efficiency is given by

A. B.P.F. – 1

B. 1 – B.P.F.

C. 1/ B.P.F.

D. 1 + B.P.F.

Answer: B

267. For large tonnage (more than 200 TR) air-conditioning applications, the compressor recommended is

A. Reciprocating

B. Rotating

C. Centrifugal

D. Screw

Answer: C

268. The wet bulb temperature during sensible cooling of air

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: C

269. A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be

A. 1/4

B. 1/3

C. 3

D. 4

Answer: D

270. A refrigerant with the highest critical pressure is

A. R-11

B. R-12

C. R-22

D. Ammonia

Answer: D

271. In aqua ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in

A. Condenser

B. Evaporator

C. Absorber

D. None of these

Answer: A

272. Most air cooled condensers are designed to operate with a temperature difference of

A. 5°C

B. 8°C

C. 14°C

D. 22°C

Answer: C

273. In a reversed Brayton cycle, the heat is absorbed by the air during

A. Isentropic compression process

B. Constant pressure cooling process

C. Isentropic expansion process

D. Constant pressure expansion process

Answer: D

274. Wet bulb temperature is the temperature of air recorded by a thermometer, when

A. It is not affected by the moisture present in the air

B. Its bulb is surrounded by a wet cloth exposed to the air

C. The moisture present in it begins to condense

D. None of the above

Answer: B

275. The difference between dry bulb temperature and dew point temperature, is called

A. Dry bulb depression

B. Wet bulb depression

C. Dew point depression

D. Degree of saturation

Answer: C

276. In mechanical refrigeration system, the refrigerant has the maximum temperature

A. In evaporator

B. Before expansion valve

C. Between compressor and condenser

D. Between condenser and evaporator

Answer: C

277. The central air conditioning system has ___________ overall efficiency as compared to individual systems.

A. Same

B. Lower

C. Higher

D. None of these

Answer: C

278. Moisture should be removed from refrigerants to avoid

A. Freezing at the expansion valve

B. Restriction to refrigerant flow

C. Corrosion of steel plates

D. All of these

Answer: D

279. The specific humidity during humidification process

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: B

280. During a refrigeration cycle, heat is rejected by the refrigerant in a

A. Compressor

B. Condenser

C. Evaporator

D. Expansion valve

Answer: B

281. In a vapour compression system, the condition of refrigerant is dry saturated vapour

A. Before entering the compressor

B. After leaving the compressor

C. Before entering the condenser

D. After leaving the condenser

Answer: A

282. During sensible cooling of air, specific humidity

A. Remains constant

B. Increases

C. Decreases

D. None of these

Answer: A

283. In a psychrometric chart, specific humidity (moisture content) lines are

A. Vertical and uniformly spaced

B. Horizontal and uniformly spaced

C. Horizontal and non-uniformly spaced

D. Curved lines

Answer: B

284. The horizontal and non-uniformly spaced lines on a psychrometric chart indicates

A. Dry bulb temperature

B. Wet bulb temperature

C. Dew point temperature

D. Specific humidity

Answer: C

285. In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

A. It considerably reduces mass of the system

B. It improves the C.O.P., as the condenser is small

C. The positive work in isentropic expansion of liquid is very small

D. It leads to significant cost reduction

Answer: C

286. Which of the following refrigerant is highly toxic and flammable?

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. R-12

Answer: A
287. The dehumidification process, on the psychrometric chart, is shown by

A. Horizontal line

B. Vertical line

C. Inclined line

D. Curved line

Answer: B

288. The wet bulb temperature at 100% relative humidity is ________ dry bulb temperature.

A. Same as

B. Lower than

C. Higher than

D. None of these

Answer: A

289. The human body feels comfortable when the heat stored in the body is

A. Positive

B. Negative

C. Zero

D. None of these

Answer: C

290. The heat rejection factor (HRF) is given by

A. 1 + C.O.P

B. 1 – C.O.P.

C. 1 + (1/C.O.P)

D. 1 – (1/C.O.P)

Answer: C

291. In order to collect liquid refrigerant and to prevent it from going to a ________, a device known as accumulator is used at the suction of compressor.

A. Compressor

B. Condenser

C. Expansion valve

D. Evaporator

Answer: A

292. The vertical and uniformly spaced lines on a psychrometric chart indicates

A. Dry bulb temperature

B. Wet bulb temperature

C. Dew point temperature

D. Specific humidity

Answer: A

293. The undesirable property of a refrigerant is

A. Non-toxic

B. Non-flammable

C. Non-explosive

D. High boiling point

Answer: D

294. The process, generally used in summer air conditioning to cool and dehumidify the air, is called

A. Humidification

B. Dehumidification

C. Heating and humidification

D. Cooling and dehumidification

Answer: D

295. The leakage in a refrigeration system using ammonia is detected by

A. Halide torch

B. Sulphur sticks

C. Soap and water

D. All of these

Answer: B

296. The lowest temperature during the cycle in a vapour compression system occurs after

A. Compression

B. Expansion

C. Condensation

D. Evaporation

Answer: D

297. In a domestic refrigerator, a capillary tube controls the flow of refrigerant from the

A. Expansion valve to the evaporator

B. Evaporator to the thermostat

C. Condenser to the expansion valve

D. Condenser to the evaporator

Answer: A

298. The refrigerant used in small tonnage commercial machines (hermetically sealed units) is

A. Ammonia

B. Carbon dioxide

C. Sulphur dioxide

D. R-12

Answer: C

299. When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be

A. Cooled and humidified

B. Cooled and dehumidified

C. Heated and humidified

D. Heated and dehumidified

Answer: A

300. A refrigerant compressor is used to

A. Raise the pressure of the refrigerant

B. Raise the temperature of the refrigerant

C. Circulate the refrigerant through the refrigerating system

D. All of the above

Answer: D

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