Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

High, of the order of 25°

Zero

Any value

As low as possible (3 to 11°C)

2. The higher temperature in vapour compression cycle occurs at

Receiver

Compressor discharge

Evaporator

Expansion valve

3. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

More

Less

Same

None of these

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

Carbon dioxide

Sulphur dioxide

Fluorine

Ammonia

6. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Temperature lines

Total heat lines

Entropy lines

7. 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

8. The optimum effective temperature for human comfort is

Not dependent on season

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

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

Suction pressure

Discharge pressure

Back pressure

Critical pressure

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

3 to 5 TR

5 to 7 TR

1 to 3 TR

0.1 to 0.3 TR

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11. The dry bulb temperature during sensible heating of air

Remains constant

None of these

Increases

Decreases

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

Simple air cooling system

Bootstrap air cooling system

Simple evaporative air cooling system

All of these

13. The lowest thermal diffusivity is of

Iron

Rubber

Aluminium

Lead

14. 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

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

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

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

None of the above

16. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

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 is the total mass of machine

One tonne refrigerant is used

17. 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 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

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

Higher critical temperature

High boiling point

High latent heat of vaporisation

Tow specific heat of liquid

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

None of the above

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

20. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is more than 1

Is less than 1

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

Lithium bromide

Carbon dioxide

R-12

Sulphur dioxide

22. Choose the correct statement

A refrigerant should have low latent heat

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

Superheat and sensible heat of a refrigerant are same

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

None of the above

Is higher than that of the entering air

Can be lower or higher than that of the entering air

Is lower than that of the entering air

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

Superheated vapour region

Wet vapour region

Sub-cooled liquid region

None of these

25. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

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

More

More/less depending on rating

Same

Less

27. 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

Increase

Reduce

Equalize

28. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of evaporator

Of freezing zone

At which refrigerant gas becomes liquid

29. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

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

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

High heat transfer rate

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31. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

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

Liquid

Saturated liquid

Wet vapour

Sub-cooled liquid

33. Carbon dioxide is

Odourless

Non-flammable

Colourless

All of these

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

Bigger

Smaller

Equal

Smaller/bigger depending on capacity

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

Compressor

Condenser

Expansion valve

Evaporator

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

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

None of these

High pressure liquid refrigerant

37. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

38. 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

39. 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

40. 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.

It reacts with copper and its alloys.

All of these

Refrigeration & Air-Conditioning Practice Set-2

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