Refrigeration & Air-Conditioning Practice Set-5

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1. 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

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

System has high C.O.P.

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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

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

Electrolux refrigerator

Vapour absorption

Vapour compression

Carnot cycle

5. 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

6. 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

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

Coefficient of performance of heat pump

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of refrigeration

8. 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?

0.5

0.8

0.25

1.25

9. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Triple point

Saturation point of vapour

10. The bypass factor for a cooling coil

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

Increases with increase in velocity of air passing through it

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

None of these

Greater than

Equal to

Less than

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

14. 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

15. 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

16. 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

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

Aluminium

Copper

Brass

Steel

20. The specific humidity during cooling and dehumidification

Decreases

None of these

Remains constant

Increases

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21. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Commercial refrigerators

Gas liquefaction

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

Copper

Steel

Brass

Aluminium

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

24. 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.

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

Increases power consumption

Increases heat transfer

Improves C.O.P. of the system

Reduces power consumption

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

50%

25%

10%

75%

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

420 kJ/ min

210 kJ/ min

840 kJ/ min

21 kJ/ min

28. 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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Vertical line

Horizontal line

Curved line

Inclined line

30. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

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31. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

32. 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

33. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant pressure lines

Constant entropy lines

Constant total heat lines

34. 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

35. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

Low boiling point

All of these

36. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

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

Vapour compression cycle

Air refrigeration cycle

None of these

Vapour absorption cycle

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

1 m3 of water

1 kg of dry air

1 m3 of dry air

1 kg of wet air

39. 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

Dew point temperature

None of these

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

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

Water and water

Ammonia and water

Ammonia and lithium bromide

Water and lithium bromide

42. The evaporator used in household refrigerators is

Non-frosting evaporator

Defrosting evaporator

None of these

Frosting evaporator

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

Equal to

More than

Less than

None of these

44. 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 1 minute

In 12 hours

45. The refrigerant for a refrigerator should have

High latent heat

Low latent heat

High sensible heat

High total heat

Refrigeration & Air-Conditioning Practice Set-5

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