Refrigeration & Air-Conditioning Practice Set-5

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1. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Air conditioning

Commercial refrigerators

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

Equal to

More than

Less than

None of these

3. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant pressure lines

Constant temperature lines

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

25%

75%

50%

10%

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

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

6. The bypass factor for a cooling coil

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

Remains unchanged with increase in velocity of air passing through it

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

8. The power per tonne of refrigeration is

3.5/C.O.P.

3.5 × C.O.P.

None of these

C.O.P/3.5

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

Ammonia and lithium bromide

Water and water

Water and lithium bromide

Ammonia and water

10. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

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

Generator

Absorber and generator

Absorber, generator and liquid pump

Liquid pump

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

210 kJ/ min

840 kJ/ min

21 kJ/ min

420 kJ/ min

13. 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

14. 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

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

Steel

Brass

Copper

Aluminium

16. 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 m3 of dry air

1 kg of dry air

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)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

18. 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

Coefficient of performance of heat pump

Refrigerating efficiency

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

In 1 hour

In 24 hours

In 12 hours

In 1 minute

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. Chaperon equation is applicable for registration at

Triple point

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

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

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

23. 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)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

None of these

Greater than

Equal to

Less than

25. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 kg 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 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

26. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

27. The specific humidity during cooling and dehumidification

None of these

Increases

Decreases

Remains constant

28. 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

29. 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

30. Ammonia is

Non-toxic

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

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

1 kg of wet air

1 m3 of water

1 kg of dry air

1 m3 of dry air

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

Electrolux refrigerator

Vapour compression

Vapour absorption

Carnot cycle

34. The desirable property of a refrigerant is

Low boiling point

High latent heat of vaporisation

High critical temperature

All of these

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

Air refrigeration cycle

None of these

Vapour compression cycle

Vapour absorption cycle

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

Horizontal line

Curved line

Inclined line

Vertical line

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?

0.8

0.5

1.25

0.25

38. 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

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

Brass

Steel

Aluminium

Copper

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

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

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

Dew point temperature

Dry bulb temperature

None of these

Wet bulb temperature

42. 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

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

1 m3 of dry air

1 m3 of water

1 kg of wet air

1 kg of dry air

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

Simple air cooling system

Bootstrap air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

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

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

Refrigeration & Air-Conditioning Practice Set-5

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