Refrigeration & Air-Conditioning Practice Set-5

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1. 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?

0.8

0.25

0.5

1.25

2. Ammonia is

Non-toxic

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

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

Increase cooling effect

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

Reduce compressor discharge temperature

Reduce compressor overheating

4. The desirable property of a refrigerant is

High critical temperature

All of these

High latent heat of vaporisation

Low boiling point

5. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

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

10%

50%

75%

25%

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

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

Weak solution to strong solution

Strong solution to weak solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

9. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

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

210 kJ/ min

21 kJ/ min

420 kJ/ min

840 kJ/ min

12. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Air conditioning

Gas liquefaction

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

Ammonia and water

Water and water

Water and lithium bromide

Ammonia and lithium bromide

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

In 1 hour

In 12 hours

In 24 hours

In 1 minute

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

Greater than

Less than

None of these

Equal to

16. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

17. 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

18. The power per tonne of refrigeration is

3.5/C.O.P.

C.O.P/3.5

3.5 × C.O.P.

None of these

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

Aluminium

Brass

Steel

Copper

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

1 m3 of water

1 kg of wet air

1 m3 of dry air

1 kg of dry air

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

Vapour absorption

Vapour compression

Carnot cycle

Electrolux refrigerator

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

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

24. 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)]

25. 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.

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

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

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

Brass

Aluminium

Copper

Steel

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

Mass of refrigerant circulated in the system is low

Power per TR is low

System has high C.O.P.

Mass of the refrigeration equipment is low

29. 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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

30. The refrigerant for a refrigerator should have

High latent heat

High total heat

High sensible heat

Low latent heat

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31. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

None of these

Dry saturated liquid refrigerant

Superheated vapour refrigerant

32. 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

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

Horizontal line

Inclined line

Vertical line

Curved line

34. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant entropy lines

Constant temperature lines

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

Simple air cooling system

Regenerative air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

36. 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 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 kg of dry air

The mass of water vapour present in 1 m³ of dry air

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

Generator

Liquid pump

Absorber, generator and liquid pump

Absorber and generator

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

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

39. 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 kg of wet air

1 m3 of wet air

40. 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

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Air refrigeration cycle

Vapour absorption cycle

None of these

Vapour compression cycle

43. 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

44. Chaperon equation is applicable for registration at

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

Triple point

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

Less than

None of these

Equal to

More than

Refrigeration & Air-Conditioning Practice Set-5

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