Refrigeration & Air-Conditioning Practice Set-5

Page 1 of 5

1. 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

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

Electrolux refrigerator

Vapour absorption

Vapour compression

Carnot cycle

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

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

Improves C.O.P. of the system

Increases power consumption

Increases heat transfer

Reduces power consumption

7. 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

1.25

0.25

0.5

8. Ammonia is

Toxic and non-inflammable

Non-toxic

Non-inflammable

Highly toxic and inflammable

9. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

10. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

Page 2 of 5

11. The evaporator used in household refrigerators is

None of these

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

12. 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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

13. Degree of saturation or percentage humidity is

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 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

14. The power per tonne of refrigeration is

3.5 × C.O.P.

3.5/C.O.P.

C.O.P/3.5

None of these

15. The refrigerant for a refrigerator should have

High latent heat

High sensible heat

Low latent heat

High total heat

16. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant pressure lines

Constant temperature lines

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

Brass

Aluminium

Copper

Steel

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

Air refrigeration cycle

Vapour compression cycle

Vapour absorption cycle

None of these

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

Inclined line

Horizontal line

Curved line

Vertical line

20. 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

Page 3 of 5

21. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

22. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

23. 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

24. The specific humidity during cooling and dehumidification

Increases

Decreases

None of these

Remains constant

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

26. 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

Reduce compressor discharge temperature

Increase cooling effect

27. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

Triple point

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

In 12 hours

In 24 hours

In 1 minute

In 1 hour

29. 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.

30. 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

Page 4 of 5

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of water

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

50%

10%

25%

75%

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

Coefficient of performance of refrigeration

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of heat pump

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

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

Water and water

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

None of these

Less than

More than

Equal to

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

Brass

Steel

Copper

Aluminium

38. 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

39. 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 ammonia vapour

Strong solution to weak solution

Weak solution to strong solution

40. The bypass factor for a cooling coil

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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Page 5 of 5

41. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Gas liquefaction

Commercial refrigerators

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

Reversed Carnot cycle

44. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

High critical temperature

Low boiling point

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

Less than

None of these

Greater than

Equal to

Refrigeration & Air-Conditioning Practice Set-5

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection

Refrigeration & Air-Conditioning Practice Set-5

Share this Now with Friends:

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection