Refrigeration & Air-Conditioning Practice Set-5

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

Vapour absorption

Electrolux refrigerator

Carnot cycle

Vapour compression

2. The evaporator used in household refrigerators is

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

None of these

3. Ammonia is

Toxic and non-inflammable

Non-inflammable

Non-toxic

Highly toxic and inflammable

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

Greater than

Less than

Equal to

None of these

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Carnot cycle

Reversed Joule cycle

6. The bypass factor for a cooling coil

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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

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

Equal to

None of these

Less than

More than

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

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

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

Regenerative air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Simple air cooling system

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

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Relative humidity

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11. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

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

In 24 hours

In 1 minute

In 12 hours

In 1 hour

13. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

Low boiling point

All of these

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

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of wet air

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

Reduce compressor discharge temperature

Reduce compressor overheating

Increase cooling effect

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

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

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

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

1 kg of dry air

1 m3 of dry air

1 m3 of water

1 kg of wet air

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

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

Water and water

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

Weak solution to strong solution

Strong solution to weak solution

Ammonia vapours to weak solution

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

Absorber, generator and liquid pump

Generator

Absorber and generator

Liquid pump

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

21 kJ/ min

840 kJ/ min

420 kJ/ min

210 kJ/ min

26. The power per tonne of refrigeration is

None of these

3.5/C.O.P.

3.5 × C.O.P.

C.O.P/3.5

27. The specific humidity during cooling and dehumidification

Decreases

None of these

Remains constant

Increases

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

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

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

Vertical line

Horizontal line

Curved line

Inclined line

30. 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)

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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31. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

32. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant pressure lines

Constant temperature lines

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

75%

50%

10%

25%

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

Reduces power consumption

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

35. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

B.P.F. - 1

1 - B. P.F.

1 + B.P.F.

1/ B.P.F.

37. The refrigerant for a refrigerator should have

High sensible heat

High total heat

Low latent heat

High latent heat

38. 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?

0.5

0.25

0.8

1.25

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

Wet bulb temperature

Dew point temperature

None of these

Dry bulb temperature

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

Air refrigeration cycle

Vapour absorption cycle

None of these

Vapour compression cycle

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41. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

Air conditioning

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

Copper

Brass

Steel

Aluminium

43. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

Triple point

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

Brass

Copper

Steel

Aluminium

45. Degree of saturation or percentage humidity is

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 m³ of dry air

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

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

Refrigeration & Air-Conditioning Practice Set-5

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