Refrigeration & Air-Conditioning Practice Set-5

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1. 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

2. Chaperon equation is applicable for registration at

Triple point

Sublimation temperature

Saturation point of vapour

Saturation point of liquid

3. 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

4. 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

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

840 kJ/ min

210 kJ/ min

420 kJ/ min

21 kJ/ min

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

75%

50%

10%

25%

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

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

Aluminium

Copper

Brass

Steel

9. The specific humidity during cooling and dehumidification

Decreases

Increases

None of these

Remains constant

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

Inclined line

Horizontal line

Curved line

Vertical line

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11. 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 mass of water vapour present in 1 m³ of dry air

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

12. 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

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

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

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

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

1 kg of wet air

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

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

Water and water

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

Wet bulb temperature

None of these

Dew point temperature

Dry bulb temperature

17. Ammonia is

Non-inflammable

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

18. 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

19. The desirable property of a refrigerant is

Low boiling point

High latent heat of vaporisation

High critical temperature

All of these

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

Greater than

None of these

Less than

Equal to

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

None of these

More than

Less than

Equal to

22. 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?

0.5

0.8

1.25

0.25

23. The evaporator used in household refrigerators is

None of these

Non-frosting evaporator

Defrosting evaporator

Frosting evaporator

24. The bypass factor for a cooling coil

Decreases 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

Increases with increase in velocity of air passing through it

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

Power per TR is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

26. 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

27. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant pressure lines

Constant entropy lines

Constant total heat lines

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

Brass

Steel

Aluminium

Copper

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

In 24 hours

In 1 hour

In 1 minute

In 12 hours

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

33. 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

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

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)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

36. 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

37. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Commercial refrigerators

Gas liquefaction

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

Weak solution to strong solution

Strong solution to weak solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

39. The refrigerant for a refrigerator should have

High latent heat

Low latent heat

High total heat

High sensible heat

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

Carnot cycle

Electrolux refrigerator

Vapour absorption

Vapour compression

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

Reduce compressor overheating

Reduce compressor discharge temperature

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

Increase cooling effect

42. 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

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

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

Increases heat transfer

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

45. 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.

B.P.F. - 1

1 + B.P.F.

Refrigeration & Air-Conditioning Practice Set-5

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