Refrigeration & Air-Conditioning Practice Set-5

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1. 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

Reduce compressor overheating

Increase cooling effect

2. 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

None of these

Wet bulb temperature

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

More than

Less than

None of these

Equal to

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

Strong solution to ammonia vapour

Strong solution to weak solution

Weak solution to strong solution

Ammonia vapours to weak solution

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

210 kJ/ min

420 kJ/ min

840 kJ/ min

21 kJ/ min

6. Ammonia is

Non-inflammable

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

8. Degree of saturation or percentage humidity is

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

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

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

1 m3 of water

1 kg of wet air

1 m3 of dry air

1 kg of dry air

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11. 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

12. 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 kg of wet air

1 m3 of wet air

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

Reduced ambient air cooling system

Bootstrap air cooling system

Regenerative air cooling system

Simple air cooling system

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

Copper

Steel

Brass

Aluminium

16. 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 refrigeration

Coefficient of performance of heat pump

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

18. 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)

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

Vertical line

Horizontal line

Curved line

Inclined line

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

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

None of these

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

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

50%

10%

25%

75%

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

1 kg of wet air

1 kg of dry air

1 m3 of water

1 m3 of dry air

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

In 24 hours

In 12 hours

In 1 minute

In 1 hour

25. 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

26. The refrigerant for a refrigerator should have

High sensible heat

Low latent heat

High total heat

High latent heat

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

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

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

Aluminium

Steel

Brass

Copper

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

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

30. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

None of these

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

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

Increases heat transfer

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Otto cycle

Reversed Carnot cycle

33. The power per tonne of refrigeration is

C.O.P/3.5

None of these

3.5 × C.O.P.

3.5/C.O.P.

34. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Greater than

None of these

Less than

Equal to

36. 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

0.25

1.25

37. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

Low boiling point

High critical temperature

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

Absorber and generator

Generator

Liquid pump

Absorber, generator and liquid pump

39. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant temperature lines

Constant total heat lines

40. The specific humidity during cooling and dehumidification

Decreases

None of these

Remains constant

Increases

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

Power per TR is low

System has high C.O.P.

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

42. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

43. 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.

44. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

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

Ammonia and lithium bromide

Ammonia and water

Water and water

Water and lithium bromide

Refrigeration & Air-Conditioning Practice Set-5

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