Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

More

None of these

Less

Same

2. 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

None of the above

Is higher than that of the entering air

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

Liquid

Sub-cooled liquid

Saturated liquid

Wet vapour

4. Reducing suction pressure in refrigeration cycle

All of these

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

Lowers evaporation temperature

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

Evaporator

Compressor

Expansion valve

Condenser

6. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

None of these

Increases

7. 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

None of the above

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

Any value

9. 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

10. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Temperature lines

Entropy lines

Total heat lines

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11. Choose the correct statement

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

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

12. 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 secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

13. Carbon dioxide is

All of these

Odourless

Non-flammable

Colourless

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

Carbon dioxide

Sulphur dioxide

Fluorine

Ammonia

15. 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

16. A one tonne refrigerating machine means that

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 of water can be converted into ice

One tonne is the total mass of machine

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

3 to 5 TR

5 to 7 TR

1 to 3 TR

0.1 to 0.3 TR

18. The lowest thermal diffusivity is of

Aluminium

Iron

Rubber

Lead

19. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

20. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid becomes vapour

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21. The optimum effective temperature for human comfort is

Same in winter and summer

Higher in winter than in summer

Not dependent on season

Lower in winter than in summer

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

High heat transfer rate

Low temperature at high altitudes

Low weight per tonne of refrigeration

Higher coefficient of performance

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

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

High pressure liquid refrigerant

None of these

24. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

More/less depending on rating

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

Simple air cooling system

Bootstrap air cooling system

All of these

Simple evaporative air cooling system

27. 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

28. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

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

The standard unit used in refrigeration problems

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

29. 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 is toxic to mucous membranes.

It reacts with copper and its alloys.

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

Equalize

Increase

None of these

Reduce

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

Smaller

Equal

Smaller/bigger depending on capacity

Bigger

32. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Receiver

Evaporator

33. The COP of a domestic refrigerator

Is equal to 1

Is more than 1

Is less than 1

Depends upon the make

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

Higher critical temperature

Tow specific heat of liquid

High boiling point

High latent heat of vaporisation

35. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

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

Discharge pressure

Back pressure

Suction pressure

Critical pressure

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

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

38. 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

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

Superheated vapour region

Wet vapour region

None of these

Sub-cooled liquid region

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

Weak solution mixes with strong solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Refrigeration & Air-Conditioning Practice Set-2

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