Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

High latent heat of vaporisation

Higher critical temperature

High boiling point

Tow specific heat of liquid

2. The lowest thermal diffusivity is of

Lead

Aluminium

Rubber

Iron

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

Condenser

Expansion valve

Evaporator

Compressor

4. Carbon dioxide is

Odourless

All of these

Colourless

Non-flammable

5. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

6. A one tonne refrigerating machine means that

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 of water can be converted into ice

One tonne is the total mass of machine

One tonne refrigerant is used

7. 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 + 2

(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 - 1

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

Same

More

None of these

Less

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

10. One ton of the refrigeration is

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 cooling effect produced by melting 1 ton of ice

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

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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

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

12. Choose the correct statement

Pre-cooling and sub-cooling bf refrigerant are same

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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

13. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Not dependent on season

Same in winter and summer

14. The dry bulb temperature during sensible heating of air

Increases

Decreases

Remains constant

None of these

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

Discharge pressure

Back pressure

Suction pressure

Critical pressure

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

More

Same

Less

More/less depending on rating

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

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

None of the above

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

Sulphur dioxide

Ammonia

Fluorine

Carbon dioxide

19. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

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

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

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21. The COP of a domestic refrigerator

Is less than 1

Is equal to 1

Depends upon the make

Is more than 1

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

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

All of these

It reacts with copper and its alloys.

23. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes vapour

24. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Is immaterial

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

Reduce

Equalize

None of these

Increase

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

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

27. 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

28. The higher temperature in vapour compression cycle occurs at

Expansion valve

Receiver

Compressor discharge

Evaporator

29. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

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

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

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

Wet vapour

Saturated liquid

Sub-cooled liquid

Liquid

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

As low as possible (3 to 11°C)

Any value

Zero

High, of the order of 25°

33. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

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

Sub-cooled liquid region

Superheated vapour region

None of these

Wet vapour region

35. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Total heat lines

Entropy lines

Temperature lines

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

Equal to critical temperature

None of the above

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

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

None of the above

Can be lower or higher than that of the entering air

Is higher than that of the entering air

Is lower than that of the entering air

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

Carbon dioxide

Lithium bromide

R-12

Sulphur dioxide

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

Smaller

Smaller/bigger depending on capacity

Equal

Bigger

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

Higher coefficient of performance

Low weight per tonne of refrigeration

High heat transfer rate

Low temperature at high altitudes

Refrigeration & Air-Conditioning Practice Set-2

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