Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

2. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Is immaterial

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

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

4. 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 - 1

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

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

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

None of these

Reduce

Increase

Equalize

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

Ammonia

Carbon dioxide

Sulphur dioxide

Fluorine

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

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

8. The dry bulb temperature during sensible heating of air

None of these

Increases

Remains constant

Decreases

9. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

The standard unit used in refrigeration problems

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

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

10. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Same in winter and summer

Not dependent on season

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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

12. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

13. During heating and dehumidification process, dry bulb temperature

None of these

Remains constant

Decreases

Increases

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

Smaller/bigger depending on capacity

Equal

Smaller

Bigger

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

Simple air cooling system

Simple evaporative air cooling system

Bootstrap air cooling system

All of these

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

Expansion valve

Condenser

Evaporator

Compressor

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

Superheated vapour region

Sub-cooled liquid region

None of these

Wet vapour region

18. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Total heat lines

Pressure lines

19. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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

One tonne refrigerant is used

One tonne of water can be converted into ice

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

High, of the order of 25°

Any value

As low as possible (3 to 11°C)

Zero

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21. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is less than 1

Is more than 1

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

Is higher than that of the entering air

Can be lower or higher than that of the entering air

None of the above

Is lower than that of the entering air

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

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

24. 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

25. Carbon dioxide is

All of these

Colourless

Non-flammable

Odourless

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

The moisture present in it begins to condense

None of the above

It is not affected by the moisture present in the air

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

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

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

High pressure liquid refrigerant

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

Equal to critical temperature

None of the above

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

29. Choose the correct statement

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

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

Superheat and sensible heat of a refrigerant are same

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

0.1 to 0.3 TR

3 to 5 TR

5 to 7 TR

1 to 3 TR

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31. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

Of freezing zone

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

High boiling point

Tow specific heat of liquid

High latent heat of vaporisation

Higher critical temperature

33. The lowest thermal diffusivity is of

Aluminium

Rubber

Iron

Lead

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

Discharge pressure

Back pressure

Suction pressure

Critical pressure

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

More/less depending on rating

Less

Same

More

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

Wet vapour

Sub-cooled liquid

Saturated liquid

Liquid

37. The higher temperature in vapour compression cycle occurs at

Expansion valve

Evaporator

Compressor discharge

Receiver

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

None of these

More

Same

Less

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

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

It is toxic to mucous membranes.

All of these

40. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

All of these

Refrigeration & Air-Conditioning Practice Set-2

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