Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Tow specific heat of liquid

High latent heat of vaporisation

Higher critical temperature

High boiling point

2. During heating and dehumidification process, dry bulb temperature

Remains constant

Decreases

None of these

Increases

3. Choose the correct statement

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

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

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

None of these

Less

Same

More

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

Fluorine

Sulphur dioxide

Ammonia

Carbon dioxide

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

Is higher than that of the entering air

None of the above

Can be lower or higher than that of the entering air

Is lower than that of the entering air

7. The higher temperature in vapour compression cycle occurs at

Receiver

Evaporator

Expansion valve

Compressor discharge

8. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

9. 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)

Zero

Any value

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

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

Equal to critical temperature

None of the above

Page 2 of 4

11. The lowest thermal diffusivity is of

Iron

Lead

Rubber

Aluminium

12. 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

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

Smaller

Equal

Smaller/bigger depending on capacity

Bigger

14. 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

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

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

Between the first heat exchanger and the secondary compressor

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

Suction pressure

Critical pressure

Discharge pressure

Back pressure

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

Higher coefficient of performance

Low weight per tonne of refrigeration

Low temperature at high altitudes

High heat transfer rate

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

Expansion valve

Condenser

Evaporator

Compressor

19. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

Increases power required per ton of refrigeration

All of these

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

All of these

Bootstrap air cooling system

Simple air cooling system

Simple evaporative air cooling system

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

Wet vapour region

Superheated vapour region

None of these

Sub-cooled liquid region

22. 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

23. 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

24. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Is immaterial

Increases heat transfer rate

25. 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

Less

More

26. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

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

The standard unit used in refrigeration problems

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

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

Sub-cooled liquid

Liquid

Saturated liquid

Wet vapour

28. 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

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

29. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Is less than 1

Depends upon the make

30. Carbon dioxide is

Odourless

All of these

Colourless

Non-flammable

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

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

32. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Entropy lines

Temperature lines

Total heat lines

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

All of these

It is toxic to mucous membranes.

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

34. 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

35. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Much above critical pressure

Critical pressure of refrigerant

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

Lithium bromide

Sulphur dioxide

R-12

Carbon dioxide

37. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid will remain liquid

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

None of these

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

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

40. The dry bulb temperature during sensible heating of air

Remains constant

None of these

Increases

Decreases

Refrigeration & Air-Conditioning Practice Set-2

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