Refrigeration & Air-Conditioning Practice Set-5

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

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

2. 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 ammonia vapour

Weak solution to strong solution

Strong solution to weak solution

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

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

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

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Refrigerating efficiency

Relative coefficient of performance

5. The refrigerant for a refrigerator should have

High latent heat

Low latent heat

High sensible heat

High total heat

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

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

Electrolux refrigerator

Vapour compression

Vapour absorption

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

None of these

9. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

10. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant temperature lines

Constant pressure lines

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

In 1 hour

In 12 hours

In 24 hours

In 1 minute

12. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

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

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

Horizontal line

Vertical line

Inclined line

Curved line

15. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

All of these

Low boiling point

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

Mass of the refrigeration equipment is low

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

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

Less than

More than

Equal to

None of these

18. 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

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

Absorber and generator

Liquid pump

Generator

Absorber, generator and liquid pump

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

Aluminium

Copper

Brass

Steel

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21. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

Increases 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

Remains unchanged with increase in velocity of air passing through it

22. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

23. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

24. 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

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

Reduced ambient air cooling system

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

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

1 m3 of wet air

1 kg of wet air

1 kg of dry air

1 m3 of dry air

27. Air refrigeration cycle is used in

Air conditioning

Commercial refrigerators

Gas liquefaction

Domestic refrigerators

28. The power per tonne of refrigeration is

3.5 × C.O.P.

None of these

3.5/C.O.P.

C.O.P/3.5

29. 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)

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

None of these

Less than

Equal to

Greater than

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

25%

75%

10%

50%

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

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

Steel

Aluminium

Brass

Copper

34. 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

35. Ammonia is

Non-inflammable

Toxic and non-inflammable

Non-toxic

Highly toxic and inflammable

36. 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 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

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

1 m3 of water

1 m3 of dry air

1 kg of dry air

1 kg of wet air

38. 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.

39. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

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

840 kJ/ min

21 kJ/ min

420 kJ/ min

210 kJ/ min

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

Increases power consumption

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

42. 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?

0.25

1.25

0.5

0.8

43. The specific humidity during cooling and dehumidification

Increases

Remains constant

Decreases

None of these

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

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

Water and lithium bromide

Ammonia and water

Water and water

Ammonia and lithium bromide

Refrigeration & Air-Conditioning Practice Set-5

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