Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

2. Ammonia is

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

Non-toxic

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

1 m3 of wet air

1 kg of wet air

1 m3 of dry air

1 kg of dry air

4. 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 - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

5. The evaporator used in household refrigerators is

Defrosting evaporator

None of these

Non-frosting evaporator

Frosting evaporator

6. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

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

Absorber and generator

Liquid pump

Absorber, generator and liquid pump

Generator

9. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Steel

Aluminium

Copper

Brass

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

Increase cooling effect

Reduce compressor discharge temperature

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

Reduce compressor overheating

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

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

Vapour absorption cycle

Air refrigeration cycle

None of these

Vapour compression cycle

14. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

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

Less than

Greater than

Equal to

None of these

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

1 m3 of dry air

1 kg of dry air

1 m3 of water

1 kg of wet air

17. The power per tonne of refrigeration is

3.5/C.O.P.

C.O.P/3.5

None of these

3.5 × C.O.P.

18. 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 mass of water vapour present in 1 m³ 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

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

Bootstrap air cooling system

Simple air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

20. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant entropy lines

Constant temperature lines

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21. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

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

Copper

Aluminium

Brass

Steel

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

Ammonia and lithium bromide

Water and water

Ammonia and water

Water and lithium bromide

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

25. 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

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

Increases power consumption

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

28. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Triple point

Saturation point of vapour

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

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

30. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Gas liquefaction

Commercial refrigerators

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

Horizontal line

Inclined line

Vertical line

Curved line

32. 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.

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

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

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

More than

Equal to

None of these

Less than

35. 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?

0.25

0.8

0.5

1.25

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

None of these

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

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

Vapour compression

Vapour absorption

Carnot cycle

Electrolux refrigerator

39. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

All of these

High critical temperature

40. 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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41. 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

42. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High latent heat

High total heat

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

10%

25%

50%

75%

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

In 1 hour

In 1 minute

In 12 hours

In 24 hours

45. 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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Refrigeration & Air-Conditioning Practice Set-5

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