Refrigeration & Air-Conditioning Practice Set-5

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

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

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

Vapour absorption cycle

Vapour compression cycle

Air refrigeration cycle

None of these

3. 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

Increase cooling effect

Reduce compressor overheating

Reduce compressor discharge temperature

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

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

6. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Gas liquefaction

Air conditioning

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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

8. 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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

9. The refrigerant for a refrigerator should have

High total heat

High latent heat

High sensible heat

Low latent heat

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

Reversed Carnot cycle

Reversed Otto cycle

Reversed Brayton cycle

Reversed Joule cycle

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

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

1 kg of dry air

12. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

Low boiling point

High critical temperature

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

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

Power per TR is low

System has high C.O.P.

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

Less than

Equal to

None of these

More than

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

Water and water

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

16. The evaporator used in household refrigerators is

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

None of these

17. 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

0.5

0.8

0.25

18. The refrigerant supplied to a compressor must be

None of these

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

Dry saturated liquid refrigerant

19. 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

20. 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

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

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

210 kJ/ min

21 kJ/ min

420 kJ/ min

840 kJ/ min

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

Improves C.O.P. of the system

Increases heat transfer

Reduces power consumption

Increases power consumption

25. 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.

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

Aluminium

Steel

Brass

Copper

27. Ammonia is

Non-inflammable

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

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

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Relative coefficient of performance

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

Absorber and generator

Absorber, generator and liquid pump

Generator

Liquid pump

30. Chaperon equation is applicable for registration at

Saturation point of liquid

Sublimation temperature

Triple point

Saturation point of vapour

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

Less than

Greater than

None of these

Equal to

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

Aluminium

Steel

Copper

Brass

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

Vapour absorption

Carnot cycle

Electrolux refrigerator

Vapour compression

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

10%

50%

25%

75%

35. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant pressure lines

Constant total heat lines

36. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

37. 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

38. 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

Dry bulb temperature

None of these

Dew point temperature

39. The power per tonne of refrigeration is

None of these

3.5 × C.O.P.

C.O.P/3.5

3.5/C.O.P.

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

1 m3 of water

1 kg of wet air

1 kg of dry air

1 m3 of dry air

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41. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

In 24 hours

In 1 minute

In 12 hours

In 1 hour

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

Curved line

Horizontal line

Inclined line

Vertical line

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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