Refrigeration & Air-Conditioning Practice Set-5

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1. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant total heat lines

Constant entropy lines

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

Strong solution to weak solution

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

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

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

None of these

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

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

5. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Sublimation temperature

Saturation point of vapour

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

Equal to

Less than

None of these

More than

7. 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

System has high C.O.P.

Power per TR is low

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

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

9. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

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

In 24 hours

In 1 hour

In 1 minute

In 12 hours

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11. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

12. The desirable property of a refrigerant is

Low boiling point

All of these

High latent heat of vaporisation

High critical temperature

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

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

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

Increases heat transfer

15. Air refrigeration cycle is used in

Commercial refrigerators

Gas liquefaction

Air conditioning

Domestic refrigerators

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

Liquid pump

Absorber, generator and liquid pump

Generator

Absorber and generator

17. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

18. 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.

B.P.F. - 1

1 + B.P.F.

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

20. 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

0.5

0.8

1.25

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21. 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

22. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

Frosting evaporator

None of these

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

Simple air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

24. 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

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

26. 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

Increases 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

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

28. Degree of saturation or percentage humidity is

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 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 m³ of dry air

29. 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

30. Ammonia is

Highly toxic and inflammable

Non-inflammable

Non-toxic

Toxic and non-inflammable

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31. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

32. 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

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

Horizontal line

Inclined line

Vertical line

Curved line

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

10%

75%

50%

25%

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

None of these

Less than

Equal to

Greater than

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

Increase cooling effect

Reduce compressor overheating

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

Reduce compressor discharge temperature

37. The refrigerant for a refrigerator should have

High total heat

High latent heat

Low latent heat

High sensible heat

38. 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

Dry bulb temperature

None of these

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

1 m3 of dry air

1 m3 of wet air

1 kg of dry air

1 kg of wet air

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

Steel

Aluminium

Copper

Brass

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41. 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)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

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

Aluminium

Steel

Brass

Copper

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

21 kJ/ min

840 kJ/ min

210 kJ/ min

420 kJ/ min

Refrigeration & Air-Conditioning Practice Set-5

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