Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Carbon dioxide is

All of these

Colourless

Non-flammable

Odourless

2. 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

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

3. 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

4. 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

Equalize

Reduce

Increase

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

Equal

Smaller/bigger depending on capacity

Bigger

Smaller

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

It is not affected by the moisture present in the air

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

The moisture present in it begins to condense

None of the above

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

Back pressure

Discharge pressure

Critical pressure

Suction pressure

8. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is equal to 1

Is more than 1

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

Between the first heat exchanger and the secondary compressor

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

10. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Is immaterial

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

None of the above

Is higher than that of the entering air

Is lower than that of the entering air

Can be lower or higher than that of the entering air

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

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

Low pressure vapour refrigerant

14. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Pressure lines

Entropy lines

15. The dry bulb temperature during sensible heating of air

Increases

Decreases

Remains constant

None of these

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

Carbon dioxide

Ammonia

Fluorine

Sulphur dioxide

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

Bootstrap air cooling system

Simple air cooling system

All of these

Simple evaporative air cooling system

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

None of the above

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

Equal to 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 + 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

20. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Evaporator

Receiver

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

Tow specific heat of liquid

High boiling point

High latent heat of vaporisation

Higher critical temperature

22. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

Not dependent on season

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

High heat transfer rate

Higher coefficient of performance

Low temperature at high altitudes

Low weight per tonne of refrigeration

24. During heating and dehumidification process, dry bulb temperature

Remains constant

None of these

Decreases

Increases

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

High, of the order of 25°

As low as possible (3 to 11°C)

Any value

Zero

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

0.1 to 0.3 TR

3 to 5 TR

1 to 3 TR

5 to 7 TR

27. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

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

All of these

It requires large displacement per TR compared to fluoro carbons.

It is toxic to mucous membranes.

It reacts with copper and its alloys.

29. 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 depending on rating

More

Less

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

Lithium bromide

R-12

Carbon dioxide

Sulphur dioxide

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31. The lowest thermal diffusivity is of

Iron

Rubber

Lead

Aluminium

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

Saturated liquid

Sub-cooled liquid

Wet vapour

Liquid

33. A one tonne refrigerating machine means that

One tonne refrigerant is used

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

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

None of these

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

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

None of these

Less

Same

More

36. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

37. 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

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

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

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

Compressor

Condenser

Evaporator

Expansion valve

40. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

All of these

Increases power required per ton of refrigeration

Refrigeration & Air-Conditioning Practice Set-2

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