Refrigeration & Air-Conditioning Practice Set-5

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1. 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 condenser

After passing through the expansion or throttle valve

2. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

50%

10%

75%

25%

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

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

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

Equal to

Greater than

None of these

Less than

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

Aluminium

Copper

Brass

Steel

7. The power per tonne of refrigeration is

3.5/C.O.P.

C.O.P/3.5

3.5 × C.O.P.

None of these

8. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

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

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

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11. 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 refrigeration

Refrigerating efficiency

Coefficient of performance of heat pump

12. 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 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

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

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

1 kg of wet air

1 m3 of water

1 m3 of dry air

1 kg of dry air

14. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

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

Less than

More than

None of these

Equal to

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

Reduce compressor discharge temperature

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

Increase cooling effect

Reduce compressor overheating

17. 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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

Strong solution to weak solution

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

20. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

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21. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

System has high C.O.P.

23. 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.

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

In 12 hours

In 1 minute

In 24 hours

In 1 hour

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

Vertical line

Horizontal line

Inclined line

Curved line

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

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

Simple air cooling system

27. 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 m3 of wet air

1 kg of dry air

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

None of these

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

29. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

Air conditioning

30. The bypass factor for a cooling coil

Increases 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

Decreases with increase in velocity of air passing through it

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

Vapour compression

Vapour absorption

Carnot cycle

Electrolux refrigerator

32. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant pressure lines

Constant total heat lines

33. 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

34. The desirable property of a refrigerant is

All of these

High critical temperature

High latent heat of vaporisation

Low boiling point

35. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

420 kJ/ min

210 kJ/ min

21 kJ/ min

840 kJ/ min

37. 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

0.8

0.5

0.25

38. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

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

Aluminium

Brass

Copper

Steel

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

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

Water and water

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

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

Increases power consumption

Increases heat transfer

Reduces power consumption

Improves C.O.P. of the system

43. Chaperon equation is applicable for registration at

Saturation point of liquid

Sublimation temperature

Triple point

Saturation point of vapour

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

45. The specific humidity during cooling and dehumidification

Remains constant

Decreases

None of these

Increases

Refrigeration & Air-Conditioning Practice Set-5

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