Refrigeration & Air-Conditioning Practice Set-5

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

Coefficient of performance of refrigeration

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of heat pump

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

3. The evaporator used in household refrigerators is

None of these

Defrosting evaporator

Non-frosting evaporator

Frosting evaporator

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

Reduced ambient air cooling system

Simple air cooling system

Bootstrap air cooling system

Regenerative air cooling system

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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

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

More than

None of these

Equal to

Less than

7. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

All of these

High critical temperature

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

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

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

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

10. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of wet air

12. 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

13. The specific humidity during cooling and dehumidification

None of these

Remains constant

Decreases

Increases

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

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

50%

10%

75%

25%

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

17. 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)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

In 1 minute

In 12 hours

In 24 hours

In 1 hour

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

1 kg of dry air

1 m3 of water

1 m3 of dry air

1 kg of wet air

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

None of these

Vapour absorption cycle

Air refrigeration cycle

Vapour compression cycle

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21. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

Air conditioning

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

23. Degree of saturation or percentage humidity is

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 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 kg of dry air

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Power per TR is low

Mass of the refrigeration equipment is low

25. The refrigerant for a refrigerator should have

High sensible heat

Low latent heat

High latent heat

High total heat

26. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant temperature lines

Constant entropy lines

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

Steel

Copper

Aluminium

Brass

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

1 - B. P.F.

1/ B.P.F.

1 + B.P.F.

B.P.F. - 1

29. 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

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

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

Liquid pump

Absorber and generator

Generator

Absorber, generator and liquid pump

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31. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Brass

Aluminium

Copper

Steel

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

Increases power consumption

Improves C.O.P. of the system

Increases heat transfer

Reduces power consumption

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

None of these

Greater than

Less than

Equal to

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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?

0.8

0.5

0.25

1.25

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

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

Water and water

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

39. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

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

Curved line

Vertical line

Horizontal line

Inclined line

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41. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

3.5/C.O.P.

None of these

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

840 kJ/ min

21 kJ/ min

420 kJ/ min

210 kJ/ min

43. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

44. 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

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

Dry bulb temperature

None of these

Dew point temperature

Wet bulb temperature

Refrigeration & Air-Conditioning Practice Set-5

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