Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

Carbon dioxide

R-12

Lithium bromide

Sulphur dioxide

3. The lowest thermal diffusivity is of

Aluminium

Rubber

Lead

Iron

4. Choose the correct statement

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

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

A refrigerant should have low latent heat

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

Same

More

Less

More/less depending on rating

6. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

7. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

8. 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

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

Expansion valve

Condenser

Compressor

Evaporator

10. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Increases power required per ton of refrigeration

All of these

Lowers compressor capacity because vapour is lighter

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

All of these

Simple air cooling system

Simple evaporative air cooling system

Bootstrap air cooling system

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

As low as possible (3 to 11°C)

Zero

Any value

High, of the order of 25°

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

Increase

Reduce

Equalize

None of these

14. Formation of frost on evaporator in refrigerator

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

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

Fluorine

Carbon dioxide

Ammonia

Sulphur dioxide

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

Tow specific heat of liquid

Higher critical temperature

High latent heat of vaporisation

High boiling point

17. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Critical pressure of refrigerant

Much above critical pressure

Much below critical pressure

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

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

Increased to a value above its critical temperature

19. 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 - 1

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

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

20. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes gas

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

Superheated vapour region

Wet vapour region

None of these

Sub-cooled liquid region

22. The COP of a domestic refrigerator

Depends upon the make

Is less than 1

Is more than 1

Is equal to 1

23. 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 is the total mass of machine

One tonne refrigerant is used

One tonne of water can be converted into ice

24. 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

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

Smaller/bigger depending on capacity

Bigger

Equal

Smaller

26. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Entropy lines

Temperature lines

Total heat lines

27. The dry bulb temperature during sensible heating of air

Increases

Decreases

None of these

Remains constant

28. Carbon dioxide is

All of these

Odourless

Non-flammable

Colourless

29. The optimum effective temperature for human comfort is

Not dependent on season

Same in winter and summer

Higher in winter than in summer

Lower in winter than in summer

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

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

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31. The higher temperature in vapour compression cycle occurs at

Expansion valve

Receiver

Compressor discharge

Evaporator

32. 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

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

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

34. 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 goes into solution

Ammonia vapour is driven out of solution

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

Saturated liquid

Liquid

Wet vapour

Sub-cooled liquid

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

Suction pressure

Discharge pressure

Critical pressure

Back pressure

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

5 to 7 TR

3 to 5 TR

0.1 to 0.3 TR

1 to 3 TR

38. 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

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

It is not affected by the moisture present in the air

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

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

Low weight per tonne of refrigeration

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

None of these

Same

More

Less

Refrigeration & Air-Conditioning Practice Set-2

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