Refrigeration & Air-Conditioning Practice Set-2

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1. The lowest thermal diffusivity is of

Aluminium

Iron

Lead

Rubber

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

Critical pressure

Back pressure

Discharge pressure

Suction pressure

3. 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

(C.O.P.)_P = (C.O.P.)_R + 2

4. 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 is driven out of solution

Ammonia vapour goes into solution

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

Reduce

None of these

Increase

Equalize

6. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Near critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

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

As low as possible (3 to 11°C)

High, of the order of 25°

Any value

Zero

9. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Total heat lines

Pressure lines

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

Ammonia

Fluorine

Sulphur dioxide

Carbon dioxide

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

Sub-cooled liquid

Saturated liquid

Wet vapour

Liquid

12. 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

13. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

Of freezing zone

14. 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

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

Superheated vapour region

Sub-cooled liquid region

None of these

Wet vapour region

16. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Evaporator

Receiver

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

It reacts with copper and its alloys.

All of these

It requires large displacement per TR compared to fluoro carbons.

It is toxic to mucous membranes.

18. 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

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

Low weight per tonne of refrigeration

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

20. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

None of these

Increases

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21. 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

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

Carbon dioxide

Lithium bromide

Sulphur dioxide

R-12

23. The optimum effective temperature for human comfort is

Not dependent on season

Same in winter and summer

Lower in winter than in summer

Higher in winter than in summer

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

Less

More

None of these

Same

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

Evaporator

Expansion valve

Compressor

Condenser

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

None of the above

Is higher than that of the entering air

Is lower than that of the entering air

Can be lower or higher than that of the entering air

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

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

None of the above

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

29. 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

Same

Less

More

30. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

Is immaterial

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31. The COP of a domestic refrigerator

Depends upon the make

Is more than 1

Is equal to 1

Is less than 1

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

Smaller

Smaller/bigger depending on capacity

Equal

Bigger

33. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

Lowers compressor capacity because vapour is lighter

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

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

Equal to critical temperature

None of the above

35. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes gas

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

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

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

0.1 to 0.3 TR

3 to 5 TR

5 to 7 TR

1 to 3 TR

38. During heating and dehumidification process, dry bulb temperature

Decreases

None of these

Remains constant

Increases

39. Carbon dioxide is

Colourless

Odourless

All of these

Non-flammable

40. One ton of the refrigeration is

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

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

The cooling effect produced by melting 1 ton of ice

Refrigeration & Air-Conditioning Practice Set-2

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