Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

High pressure liquid refrigerant

2. Choose the correct statement

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

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

3. The COP of a domestic refrigerator

Is more than 1

Is less than 1

Is equal to 1

Depends upon the make

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

Increase

Reduce

None of these

Equalize

5. Carbon dioxide is

Non-flammable

All of these

Colourless

Odourless

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

It reacts with copper and its alloys.

It is toxic to mucous membranes.

All of these

It requires large displacement per TR compared to fluoro carbons.

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

None of these

Same

Less

More

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

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

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

Equal to critical temperature

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

10. During heating and dehumidification process, dry bulb temperature

Remains constant

None of these

Decreases

Increases

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

Sub-cooled liquid

Saturated liquid

Liquid

Wet vapour

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

High, of the order of 25°

Any value

As low as possible (3 to 11°C)

Zero

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

14. The higher temperature in vapour compression cycle occurs at

Receiver

Evaporator

Compressor discharge

Expansion valve

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

Low temperature at high altitudes

Low weight per tonne of refrigeration

High heat transfer rate

Higher coefficient of performance

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

Can be lower or higher than that of the entering air

Is lower than that of the entering air

Is higher than that of the entering air

None of the above

17. 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

18. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

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

None of these

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

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

More/less depending on rating

Less

More

Same

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21. 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

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

R-12

Sulphur dioxide

Lithium bromide

Carbon dioxide

23. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Pressure lines

Entropy lines

Total heat lines

24. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid becomes solid

25. A one tonne refrigerating machine means that

One tonne refrigerant is used

One tonne is the total mass of machine

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

26. 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

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

Smaller/bigger depending on capacity

Bigger

Equal

Smaller

28. 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

29. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

30. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

Of cooling medium

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31. The lowest thermal diffusivity is of

Iron

Rubber

Lead

Aluminium

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

High boiling point

Tow specific heat of liquid

Higher critical temperature

High latent heat of vaporisation

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

Evaporator

Expansion valve

Compressor

Condenser

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

Back pressure

Suction pressure

Discharge pressure

Critical pressure

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

0.1 to 0.3 TR

1 to 3 TR

5 to 7 TR

3 to 5 TR

36. 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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

None of the above

37. 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

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

Sulphur dioxide

Carbon dioxide

Fluorine

Ammonia

39. 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

40. The dry bulb temperature during sensible heating of air

Decreases

Increases

Remains constant

None of these

Refrigeration & Air-Conditioning Practice Set-2

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