Refrigeration & Air-Conditioning Practice Set-5

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1. 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

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

In 1 minute

In 24 hours

In 12 hours

In 1 hour

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

4. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

5. 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

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

10%

25%

50%

75%

7. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

8. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of vapour

Saturation point of liquid

Triple point

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

10. 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

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

12. Degree of saturation or percentage humidity is

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 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

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

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

Air refrigeration cycle

Vapour absorption cycle

None of these

Vapour compression cycle

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

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

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

Ammonia and water

Water and water

Water and lithium bromide

Ammonia and lithium bromide

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

Brass

Aluminium

Steel

Copper

18. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High total heat

High sensible heat

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

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

Carnot cycle

Electrolux refrigerator

Vapour absorption

Vapour compression

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21. 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.

22. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

Air conditioning

23. 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.

Mass of the refrigeration equipment is low

Power per TR is low

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

25. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

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

Less than

More than

None of these

Equal to

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

28. 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

29. The power per tonne of refrigeration is

None of these

3.5/C.O.P.

3.5 × C.O.P.

C.O.P/3.5

30. 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

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31. 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

Wet bulb temperature

Dew point temperature

None of these

32. 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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

34. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant entropy lines

Constant temperature lines

35. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

Non-inflammable

36. 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

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

Liquid pump

Absorber and generator

Generator

Absorber, generator and liquid pump

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

420 kJ/ min

210 kJ/ min

21 kJ/ min

840 kJ/ min

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

1 kg of dry air

1 m3 of water

1 m3 of dry air

1 kg of wet air

40. The desirable property of a refrigerant is

All of these

Low boiling point

High latent heat of vaporisation

High critical temperature

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

Less than

Greater than

Equal to

None of these

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

Inclined line

Horizontal line

Curved line

Vertical line

43. The specific humidity during cooling and dehumidification

Remains constant

None of these

Decreases

Increases

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

Brass

Aluminium

Copper

Steel

45. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

Refrigeration & Air-Conditioning Practice Set-5

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