Refrigeration & Air-Conditioning Practice Set-5

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1. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

2. 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

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

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

Regenerative air cooling system

Bootstrap air cooling system

Simple air cooling system

Reduced ambient air cooling system

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

Horizontal line

Inclined line

Curved line

Vertical line

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

Increases heat transfer

Increases power consumption

Reduces power consumption

Improves C.O.P. of the system

6. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant temperature lines

Constant entropy lines

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

Reduce compressor discharge temperature

Reduce compressor overheating

Increase cooling effect

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

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

10. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High sensible heat

High latent heat

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

Less than

Greater than

None of these

Equal to

12. 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

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

In 1 hour

In 24 hours

In 12 hours

In 1 minute

14. 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 m3 of wet air

1 kg of wet air

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

Brass

Copper

Steel

Aluminium

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

Vapour absorption cycle

None of these

Vapour compression cycle

Air refrigeration cycle

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

18. 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

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

Equal to

Less than

More than

None of these

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

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

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21. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Non-frosting evaporator

Defrosting evaporator

22. The specific humidity during cooling and dehumidification

Remains constant

None of these

Decreases

Increases

23. 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

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

21 kJ/ min

420 kJ/ min

840 kJ/ min

210 kJ/ min

25. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

3.5/C.O.P.

None of these

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

1 + B.P.F.

1 - B. P.F.

1/ B.P.F.

B.P.F. - 1

27. 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

Coefficient of performance of heat pump

Refrigerating efficiency

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

Ammonia and lithium bromide

Water and lithium bromide

Water and water

Ammonia and water

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

Ammonia vapours to weak solution

Strong solution to ammonia vapour

Strong solution to weak solution

Weak solution to strong solution

30. 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

0.8

0.25

0.5

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31. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

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. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Triple point

Sublimation temperature

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

75%

25%

10%

50%

35. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

Dew point temperature

Wet bulb temperature

None of these

Dry bulb temperature

36. Ammonia is

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

Non-toxic

37. 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

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

Absorber, generator and liquid pump

Generator

Liquid pump

Absorber and generator

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

Brass

Aluminium

Steel

Copper

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

Vapour compression

Vapour absorption

Carnot cycle

Electrolux refrigerator

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

42. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

44. The desirable property of a refrigerant is

High critical temperature

All of these

Low boiling point

High latent heat of vaporisation

45. Degree of saturation or percentage humidity is

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 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

Refrigeration & Air-Conditioning Practice Set-5

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