Refrigeration & Air-Conditioning Practice Set-5

Page 1 of 5

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

Vapour absorption

Vapour compression

Electrolux refrigerator

Carnot cycle

2. 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

1.25

0.5

3. The desirable property of a refrigerant is

All of these

Low boiling point

High latent heat of vaporisation

High critical temperature

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

Dry bulb temperature

None of these

Dew point temperature

Wet bulb temperature

5. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Mass of the refrigeration equipment is low

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

Inclined line

Horizontal line

Vertical line

Curved line

8. 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

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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

10. The bypass factor for a cooling coil

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

May increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

Page 2 of 5

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

Reduce compressor overheating

Reduce compressor discharge temperature

Increase cooling effect

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

12. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant total heat lines

Constant pressure lines

13. The power per tonne of refrigeration is

None of these

C.O.P/3.5

3.5 × C.O.P.

3.5/C.O.P.

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

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

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

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

840 kJ/ min

210 kJ/ min

21 kJ/ min

420 kJ/ min

17. Air refrigeration cycle is used in

Air conditioning

Commercial refrigerators

Gas liquefaction

Domestic refrigerators

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

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

None of these

Greater than

Less than

Equal to

20. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

Page 3 of 5

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

22. 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 kg of dry air

The mass of water vapour present in 1 m³ 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

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Joule cycle

Reversed Brayton cycle

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

Aluminium

Steel

Copper

Brass

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

Increases power consumption

Improves C.O.P. of the system

Reduces power consumption

Increases heat transfer

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

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

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

Liquid pump

Generator

Absorber, generator and liquid pump

Absorber and generator

28. The specific humidity during cooling and dehumidification

None of these

Increases

Decreases

Remains constant

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

Less than

None of these

Equal to

More than

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

In 12 hours

In 1 minute

In 24 hours

In 1 hour

Page 4 of 5

31. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

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

Steel

Copper

Brass

Aluminium

33. 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 heat pump

Refrigerating efficiency

Coefficient of performance of refrigeration

34. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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

Water and water

Ammonia and water

Ammonia and lithium bromide

Water and lithium bromide

36. The refrigerant for a refrigerator should have

High latent heat

High sensible heat

Low latent heat

High total heat

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

50%

75%

25%

10%

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

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

None of these

39. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

1/ B.P.F.

B.P.F. - 1

1 + B.P.F.

1 - B. P.F.

40. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-inflammable

Non-toxic

Page 5 of 5

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

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

Bootstrap air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

Simple air cooling system

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

44. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

None of these

Non-frosting evaporator

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

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

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