Refrigeration & Air-Conditioning Practice Set-5

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

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

Increases heat transfer

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

Copper

Brass

Steel

Aluminium

3. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant temperature lines

Constant total heat lines

4. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

1 + B.P.F.

B.P.F. - 1

1 - B. P.F.

1/ B.P.F.

5. 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

6. 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

Refrigerating efficiency

Coefficient of performance of heat pump

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

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

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

9. Ammonia is

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

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

1 kg of wet air

1 kg of dry air

1 m3 of wet air

1 m3 of dry air

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11. 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

12. Air refrigeration cycle is used in

Domestic refrigerators

Commercial refrigerators

Gas liquefaction

Air conditioning

13. The desirable property of a refrigerant is

Low boiling point

High latent heat of vaporisation

High critical temperature

All of these

14. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

15. 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 ammonia vapour

Strong solution to weak solution

16. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

17. The refrigerant for a refrigerator should have

High latent heat

High sensible heat

Low latent heat

High total heat

18. 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 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 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

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Simple air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

22. The bypass factor for a cooling coil

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

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

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

Inclined line

Vertical line

Horizontal line

Curved line

25. The specific humidity during cooling and dehumidification

None of these

Decreases

Remains constant

Increases

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

27. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

Frosting evaporator

None of these

28. 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

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

None of these

Vapour absorption cycle

Air refrigeration cycle

Vapour compression cycle

30. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

None of these

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

840 kJ/ min

420 kJ/ min

210 kJ/ min

21 kJ/ min

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

1 m3 of water

1 m3 of dry air

1 kg of dry air

1 kg of wet air

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

None of these

Equal to

Less than

More than

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)

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

35. 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

36. The power per tonne of refrigeration is

3.5/C.O.P.

None of these

3.5 × C.O.P.

C.O.P/3.5

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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

Relative humidity

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

System has high C.O.P.

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

Power per TR is low

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

Brass

Aluminium

Copper

Steel

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

Greater than

None of these

Less than

Equal to

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

Ammonia and water

Ammonia and lithium bromide

Water and lithium bromide

Water and water

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

50%

10%

25%

75%

43. 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?

1.25

0.25

0.5

0.8

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

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

Reduce compressor discharge temperature

Reduce compressor overheating

Increase cooling effect

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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