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 + 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

2. 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

3. 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

4. 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

5. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

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

None of the above

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Is higher than that of the entering air

7. 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

8. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Expansion valve

Evaporator

9. 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

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

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

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11. 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 reacts with copper and its alloys.

It is toxic to mucous membranes.

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

Same

Less

More/less depending on rating

More

13. 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

14. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

None of these

Remains constant

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

Wet vapour

Sub-cooled liquid

Saturated liquid

Liquid

16. The dry bulb temperature during sensible heating of air

None of these

Increases

Decreases

Remains constant

17. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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

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

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

Between the secondary compressor and the second heat exchanger

19. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Pressure lines

Entropy lines

Total heat lines

20. 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

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

Discharge pressure

Back pressure

Critical pressure

Suction pressure

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

Compressor

Condenser

Evaporator

Expansion valve

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

Same

None of these

Less

More

24. 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 refrigeration effect to produce 1 ton of ice at NTP conditions

The standard unit used in refrigeration problems

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

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

Simple air cooling system

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

Lithium bromide

Carbon dioxide

R-12

Sulphur dioxide

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

Sulphur dioxide

Carbon dioxide

Ammonia

Fluorine

28. The lowest thermal diffusivity is of

Iron

Aluminium

Rubber

Lead

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

Low pressure vapour refrigerant

None of these

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

30. Condensing temperature in a refrigerator is the temperature

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

Of freezing zone

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

32. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Is equal to 1

Depends upon the make

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

Equal

Smaller/bigger depending on capacity

Bigger

Smaller

34. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

35. 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

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

Superheated vapour region

None of these

Wet vapour region

Sub-cooled liquid region

37. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Not dependent on season

Same in winter and summer

38. 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

Increase

Reduce

39. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Is immaterial

Increases heat transfer rate

40. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

Much below critical pressure

Refrigeration & Air-Conditioning Practice Set-2

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