Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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 + 2

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

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

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

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

3. 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

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

Discharge pressure

Suction pressure

Critical pressure

Back pressure

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

Low temperature at high altitudes

High heat transfer rate

Higher coefficient of performance

Low weight per tonne of refrigeration

6. 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

7. The COP of a domestic refrigerator

Depends upon the make

Is less than 1

Is more than 1

Is equal to 1

8. 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

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

None of the above

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

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

Compressor

Condenser

Evaporator

Expansion valve

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

It is toxic to mucous membranes.

It reacts with copper and its alloys.

All of these

It requires large displacement per TR compared to fluoro carbons.

12. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of freezing zone

At which refrigerant gas becomes liquid

Of evaporator

13. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Total heat lines

Pressure lines

Temperature lines

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

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

5 to 7 TR

15. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Evaporator

Expansion valve

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

Smaller

Equal

Smaller/bigger depending on capacity

Bigger

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

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

18. The lowest thermal diffusivity is of

Lead

Rubber

Aluminium

Iron

19. 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

20. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

Page 3 of 4

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

Equalize

Reduce

None of these

Increase

22. 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

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

Less

None of these

Same

More

24. Formation of frost on evaporator in refrigerator

Is immaterial

Increases heat transfer rate

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

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

Sub-cooled liquid region

Superheated vapour region

Wet vapour region

None of these

26. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Much below critical pressure

Near critical pressure

Critical pressure of refrigerant

27. Choose the correct statement

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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

28. The dry bulb temperature during sensible heating of air

Increases

Remains constant

Decreases

None of these

29. 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

30. 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

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31. Carbon dioxide is

All of these

Colourless

Odourless

Non-flammable

32. 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

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

Sulphur dioxide

Lithium bromide

Carbon dioxide

R-12

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

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

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

All of these

Simple evaporative air cooling system

Bootstrap air cooling system

Simple air cooling system

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

Sub-cooled liquid

Saturated liquid

Wet vapour

Liquid

37. 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

38. One ton of the refrigeration is

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

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

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

Fluorine

Sulphur dioxide

Ammonia

Carbon dioxide

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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