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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

2. 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.

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

In 1 minute

In 24 hours

In 12 hours

In 1 hour

4. The refrigerant supplied to a compressor must be

None of these

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

5. The power per tonne of refrigeration is

None of these

3.5/C.O.P.

3.5 × C.O.P.

C.O.P/3.5

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

Greater than

None of these

Equal to

Less than

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

Brass

Aluminium

Copper

Steel

8. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

9. The desirable property of a refrigerant is

All of these

High critical temperature

High latent heat of vaporisation

Low boiling point

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

10%

50%

75%

25%

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

More than

Less than

None of these

Equal to

12. 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

Power per TR is low

Mass of refrigerant circulated in the system is low

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

14. The specific humidity during cooling and dehumidification

Increases

Remains constant

None of these

Decreases

15. 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 dry air

1 m3 of wet air

16. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Sublimation temperature

Saturation point of liquid

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

None of these

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

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

1 kg of dry air

1 m3 of dry air

1 m3 of water

1 kg of wet air

20. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

Remains unchanged 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

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

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

Reduces power consumption

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

23. 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

0.5

0.8

0.25

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

Vertical line

Horizontal line

Inclined line

Curved line

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

1 kg of dry air

1 m3 of water

1 kg of wet air

1 m3 of dry air

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

Vapour absorption

Vapour compression

Carnot cycle

Electrolux refrigerator

27. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

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

Reduced ambient air cooling system

Simple air cooling system

Regenerative air cooling system

Bootstrap air cooling system

29. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant total heat lines

Constant entropy lines

Constant pressure lines

30. 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

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

Ammonia and water

Water and lithium bromide

Water and water

Ammonia and lithium bromide

32. 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 weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

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

Reversed Brayton cycle

Reversed Joule cycle

Reversed Carnot cycle

Reversed Otto cycle

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

21 kJ/ min

210 kJ/ min

420 kJ/ min

840 kJ/ min

35. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

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

Copper

Steel

Brass

Aluminium

37. 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

Dry bulb temperature

None of these

Wet bulb temperature

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

Absorber and generator

Absorber, generator and liquid pump

Generator

Liquid pump

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

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Refrigerating efficiency

Relative coefficient of performance

40. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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41. Ammonia is

Toxic and non-inflammable

Non-toxic

Non-inflammable

Highly toxic and inflammable

42. Air refrigeration cycle is used in

Air conditioning

Commercial refrigerators

Domestic refrigerators

Gas liquefaction

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

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

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

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

Refrigeration & Air-Conditioning Practice Set-5

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