Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by

(C.O.P)_P = (C.O.P)_R - 1

(C.O.P)_P = (C.O.P)_R

(C.O.P.)_P = (C.O.P.)_R + 1

(C.O.P.)_P = (C.O.P.)_R + 2

2. In a vapour compression cycle, the refrigerant immediately after expansion valve is

Saturated liquid

Wet vapour

Liquid

Sub-cooled liquid

3. In a pressure enthalpy chart, the space to the left of the saturated liquid line represents

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

None of these

4. Carbon dioxide is

Odourless

Colourless

All of these

Non-flammable

5. The evaporator changes the low pressure liquid refrigerant from the expansion valve into

Low pressure vapour refrigerant

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

6. In refrigerators, the temperature difference between the evaporating refrigerant and the medium being cooled should be

Any value

Zero

As low as possible (3 to 11°C)

High, of the order of 25°

7. The evolution of heat of solution takes place in ammonia absorption plant when

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

8. The lowest thermal diffusivity is of

Iron

Aluminium

Lead

Rubber

9. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Temperature lines

Entropy lines

Total heat lines

10. During heating and humidification, the final relative humidity of air

Is lower than that of the entering air

Can be lower or higher than that of the entering air

None of the above

Is higher than that of the entering air

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11. In a bootstrap air evaporative cooling system, the evaporator is provided

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

12. Pick up the wrong statement. A refrigerant should have

High boiling point

High latent heat of vaporisation

Tow specific heat of liquid

Higher critical temperature

13. The coefficient of performance of a domestic refrigerator is ________ as compared to a domestic air-conditioner.

None of these

Same

Less

More

14. The pressure at the inlet of a refrigerant compressor is called

Suction pressure

Critical pressure

Back pressure

Discharge pressure

15. Which of the following statement is correct for ammonia as a refrigerant?

It requires large displacement per TR compared to fluoro carbons.

It is toxic to mucous membranes.

All of these

It reacts with copper and its alloys.

16. The optimum effective temperature for human comfort is

Not dependent on season

Lower in winter than in summer

Same in winter and summer

Higher in winter than in summer

17. Dry bulb temperature is the temperature of air recorded by a thermometer, when

The moisture present in it begins to condense

It is not affected by the moisture present in the air

Its bulb is surrounded by a wet cloth exposed to the air

None of the above

18. Which of the following refrigerant has the maximum ozone depletion potential in the stratosphere?

Carbon dioxide

Fluorine

Ammonia

Sulphur dioxide

19. The COP of a domestic refrigerator

Is less than 1

Is equal to 1

Depends upon the make

Is more than 1

20. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

Remains constant

None of these

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21. Presence of moisture in a refrigerant affects the working of

Expansion valve

Evaporator

Condenser

Compressor

22. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

23. In vapour compression cycle, the condition of refrigerant is high pressure saturated liquid

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

24. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

25. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

Lowers evaporation temperature

26. The capacity of a domestic refrigerator is in the range of

3 to 5 TR

0.1 to 0.3 TR

5 to 7 TR

1 to 3 TR

27. One ton of the refrigeration is

The standard unit used in refrigeration problems

The refrigeration effect to produce 1 ton of ice at NTP conditions

The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

The cooling effect produced by melting 1 ton of ice

28. If a gas is to be liquefied, its temperature must be

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

Equal to critical temperature

29. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of freezing zone

At which refrigerant gas becomes liquid

Of cooling medium

30. The suction pipe diameter of refrigerating unit compressor in comparison to delivery side is

Bigger

Smaller/bigger depending on capacity

Equal

Smaller

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31. In aircraft, air refrigeration Cycle is used because of

Higher coefficient of performance

Low weight per tonne of refrigeration

Low temperature at high altitudes

High heat transfer rate

32. Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.

Equalize

None of these

Increase

Reduce

33. Choose the correct statement

Superheat and sensible heat of a refrigerant are same

If operating temperature of system is low, then refrigerant with low boiling point should be used

Pre-cooling and sub-cooling bf refrigerant are same

A refrigerant should have low latent heat

34. The higher temperature in vapour compression cycle occurs at

Receiver

Compressor discharge

Evaporator

Expansion valve

35. If the evaporator temperature of a plant is lowered, keeping the condenser temperature constant, the h.p. of compressor required will be

Less

More/less depending on rating

Same

More

36. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

Increases

None of these

37. The air cooling system mostly used in transport type aircrafts is

Simple air cooling system

All of these

Simple evaporative air cooling system

Bootstrap air cooling system

38. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid will remain liquid

39. The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and

R-12

Lithium bromide

Carbon dioxide

Sulphur dioxide

40. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne of water can be converted into ice

One tonne refrigerant is used

One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

Refrigeration & Air-Conditioning Practice Set-2

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