Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Sub-cooled liquid

Wet vapour

Liquid

Saturated liquid

2. The COP of a domestic refrigerator

Depends upon the make

Is equal to 1

Is less than 1

Is more than 1

3. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

4. Choose the correct statement

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

A refrigerant should have low latent heat

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

Smaller

Bigger

Smaller/bigger depending on capacity

Equal

6. 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

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

As low as possible (3 to 11°C)

Any value

High, of the order of 25°

Zero

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

Sulphur dioxide

Carbon dioxide

R-12

Lithium bromide

9. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

None of these

Increases

10. 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

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

Expansion valve

Compressor

Condenser

Evaporator

12. 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 combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

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

Carbon dioxide

Sulphur dioxide

Ammonia

Fluorine

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

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

15. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Increases heat transfer rate

Is immaterial

16. 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

(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

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

0.1 to 0.3 TR

5 to 7 TR

3 to 5 TR

1 to 3 TR

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

Simple air cooling system

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

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

Sub-cooled liquid region

Superheated vapour region

None of these

Wet vapour region

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

Discharge pressure

Back pressure

Critical pressure

Suction pressure

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

Is higher than that of the entering air

None of the above

Is lower than that of the entering air

Can be lower or higher than that of the entering air

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

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

Low weight per tonne of refrigeration

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

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

24. 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

25. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid will remain liquid

26. Condensing temperature in a refrigerator is the temperature

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

Of freezing zone

27. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Receiver

Expansion valve

28. 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.

All of these

It reacts with copper and its alloys.

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

None of these

More

Less

Same

30. One ton of the refrigeration is

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

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

Page 4 of 4

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

High boiling point

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

32. The lowest thermal diffusivity is of

Rubber

Iron

Lead

Aluminium

33. 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

Weak solution mixes with strong solution

34. 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 refrigerant is used

One tonne is the total mass of machine

35. Carbon dioxide is

All of these

Colourless

Non-flammable

Odourless

36. 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

37. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

38. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

None of these

Remains constant

39. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Temperature lines

Pressure lines

Total heat lines

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

Refrigeration & Air-Conditioning Practice Set-2

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