Refrigeration & Air-Conditioning Practice Set-5

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1. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant entropy lines

Constant temperature lines

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

Inclined line

Horizontal line

Curved line

Vertical line

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

Absorber, generator and liquid pump

Absorber and generator

Generator

Liquid pump

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

5. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

All of these

Low boiling point

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

Greater than

None of these

Equal to

Less than

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Otto cycle

Reversed Carnot cycle

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

None of these

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

In 12 hours

In 24 hours

In 1 hour

In 1 minute

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

Vapour absorption

Electrolux refrigerator

Carnot cycle

Vapour compression

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11. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

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

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

Reduce compressor discharge temperature

Increase cooling effect

Reduce compressor overheating

13. Air refrigeration cycle is used in

Commercial refrigerators

Gas liquefaction

Air conditioning

Domestic refrigerators

14. 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)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

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

1/ B.P.F.

B.P.F. - 1

1 - B. P.F.

1 + B.P.F.

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

Equal to

Less than

More than

None of these

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

Copper

Brass

Aluminium

Steel

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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

20. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

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21. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of vapour

Saturation point of liquid

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

Strong solution to ammonia vapour

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to weak solution

23. 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 h_A = Enthalpy of air at the end of dehumidification process)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

24. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

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

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Mass of the refrigeration equipment is low

26. Ammonia is

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

Non-toxic

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Before passing through the condenser

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

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

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

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

10%

75%

25%

50%

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

Vapour absorption cycle

None of these

Air refrigeration cycle

Vapour compression cycle

32. Degree of saturation or percentage humidity is

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

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

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

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

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

Ammonia and lithium bromide

Water and lithium bromide

Ammonia and water

Water and water

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

1 m3 of dry air

1 m3 of water

1 kg of wet air

1 kg of dry air

35. The specific humidity during cooling and dehumidification

None of these

Remains constant

Increases

Decreases

36. 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?

1.25

0.5

0.8

0.25

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

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

210 kJ/ min

21 kJ/ min

840 kJ/ min

420 kJ/ min

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

1 kg of dry air

1 kg of wet air

1 m3 of wet air

1 m3 of dry air

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

Copper

Aluminium

Steel

Brass

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

Relative coefficient of performance

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Refrigerating efficiency

43. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

None of these

Defrosting evaporator

44. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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

45. The power per tonne of refrigeration is

C.O.P/3.5

None of these

3.5 × C.O.P.

3.5/C.O.P.

Refrigeration & Air-Conditioning Practice Set-5

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