Refrigeration & Air-Conditioning Practice Set-5

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

Greater than

Equal to

None of these

Less than

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

Regenerative air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Simple air cooling system

3. The refrigerant for a refrigerator should have

High total heat

High sensible heat

Low latent heat

High latent heat

4. 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.

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

6. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant entropy lines

Constant temperature lines

Constant total heat lines

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

Absorber, generator and liquid pump

Generator

Absorber and generator

Liquid pump

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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

9. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Defrosting evaporator

Frosting evaporator

10. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Domestic refrigerators

Commercial refrigerators

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

12. 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

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

50%

25%

10%

75%

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

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

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

Increases heat transfer

Reduces power consumption

Improves C.O.P. of the system

Increases power consumption

16. Chaperon equation is applicable for registration at

Saturation point of liquid

Triple point

Sublimation temperature

Saturation point of vapour

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

Before entering the compressor

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

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

Carnot cycle

Vapour compression

Vapour absorption

Electrolux refrigerator

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

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

Reversed Brayton cycle

20. 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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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21. 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

None of these

Wet bulb temperature

Dew point temperature

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

Reduce compressor discharge temperature

Reduce compressor overheating

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

Increase cooling effect

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

24. 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

0.25

1.25

0.5

25. 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

26. 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

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

None of these

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

28. 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

29. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

30. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

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

Ammonia and water

Water and lithium bromide

Water and water

Ammonia and lithium bromide

32. 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

33. 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 refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

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

1 kg of dry air

1 m3 of wet air

1 m3 of dry air

1 kg of wet air

35. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

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

Copper

Steel

Brass

Aluminium

37. 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

Relative coefficient of performance

Refrigerating efficiency

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

Brass

Copper

Aluminium

Steel

39. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

Low boiling point

High critical temperature

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

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Curved lines

Vertical and uniformly spaced

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41. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

42. 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

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

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

Equal to

Less than

More than

None of these

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

Vertical line

Curved line

Horizontal line

Inclined line

45. Ammonia is

Highly toxic and inflammable

Non-inflammable

Non-toxic

Toxic and non-inflammable

Refrigeration & Air-Conditioning Practice Set-5

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