Refrigeration & Air-Conditioning Practice Set-5

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

In 1 minute

In 24 hours

In 12 hours

In 1 hour

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

3. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

4. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant entropy lines

Constant temperature lines

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

None of these

More than

Equal to

Less than

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

None of these

Less than

Equal to

Greater than

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

System has high C.O.P.

Mass of the refrigeration equipment is low

Power per TR is low

Mass of refrigerant circulated in the system is low

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

1 kg of dry air

1 m3 of water

1 kg of wet air

1 m3 of dry air

9. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

10. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

1 m3 of wet air

1 m3 of dry air

1 kg of wet air

1 kg of dry air

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

Steel

Brass

Aluminium

Copper

13. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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

Vapour absorption

Electrolux refrigerator

Vapour compression

Carnot cycle

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

Vertical line

Curved line

Inclined line

Horizontal line

16. Degree of saturation or percentage humidity is

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

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

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

Dew point temperature

Wet bulb temperature

Relative humidity

Dry bulb temperature

18. 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

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

20. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

None of these

3.5/C.O.P.

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21. The specific humidity during cooling and dehumidification

Decreases

Increases

Remains constant

None of these

22. Ammonia is

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

23. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

None of these

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

Increases heat transfer

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

25. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Commercial refrigerators

Gas liquefaction

26. 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

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

Air refrigeration cycle

Vapour compression cycle

None of these

Vapour absorption cycle

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

Reversed Carnot cycle

Reversed Joule cycle

Reversed Otto cycle

Reversed Brayton cycle

29. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Decreases 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

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

Aluminium

Brass

Steel

Copper

32. The desirable property of a refrigerant is

All of these

Low boiling point

High critical temperature

High latent heat of vaporisation

33. 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.

34. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

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

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

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

Absorber, generator and liquid pump

Generator

Liquid pump

Absorber and generator

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

39. 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

Ammonia vapours to weak solution

Strong solution to weak solution

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

Increase cooling effect

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

Reduce compressor discharge temperature

Reduce compressor overheating

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41. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

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

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Simple air cooling system

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

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Refrigerating efficiency

Relative coefficient of performance

44. 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

0.25

0.8

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

25%

10%

50%

75%

Refrigeration & Air-Conditioning Practice Set-5

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