Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

2. 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.

3. Condensing temperature in a refrigerator is the temperature

Of evaporator

At which refrigerant gas becomes liquid

Of freezing zone

Of cooling medium

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

Simple air cooling system

All of these

Simple evaporative air cooling system

Bootstrap air cooling system

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

Equalize

None of these

Increase

Reduce

6. During heating and dehumidification process, dry bulb temperature

Increases

None of these

Decreases

Remains constant

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

None of these

Superheated vapour region

Sub-cooled liquid region

Wet vapour region

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

None of the above

It is not affected by the moisture present in the air

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

The moisture present in it begins to condense

9. The lowest thermal diffusivity is of

Aluminium

Iron

Lead

Rubber

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

Higher coefficient of performance

Low temperature at high altitudes

Low weight per tonne of refrigeration

High heat transfer rate

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

5 to 7 TR

1 to 3 TR

0.1 to 0.3 TR

3 to 5 TR

12. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes solid

13. 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

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

Equal to critical temperature

None of the above

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

15. 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 second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

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

Compressor

Evaporator

Condenser

Expansion valve

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

Saturated liquid

Sub-cooled liquid

Wet vapour

Liquid

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

Same

None of these

More

Less

19. 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 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

20. 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

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21. The COP of a domestic refrigerator

Is equal to 1

Is more than 1

Depends upon the make

Is less than 1

22. Choose the correct statement

Pre-cooling and sub-cooling bf refrigerant are same

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

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

Any value

High, of the order of 25°

As low as possible (3 to 11°C)

Zero

24. 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

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

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

25. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

Much below critical pressure

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

Can be lower or higher than that of the entering air

None of the above

Is lower than that of the entering air

Is higher than that of the entering air

27. 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

28. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Expansion valve

Evaporator

Receiver

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

Low pressure vapour refrigerant

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

30. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

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

Suction pressure

Back pressure

Critical pressure

Discharge pressure

32. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

None of these

Increases

33. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

34. The optimum effective temperature for human comfort is

Not dependent on season

Lower in winter than in summer

Same in winter and summer

Higher in winter than in summer

35. 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

Ammonia vapour is driven out of solution

36. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Total heat lines

Pressure lines

Temperature lines

37. Carbon dioxide is

Non-flammable

All of these

Odourless

Colourless

38. 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

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

Smaller

Smaller/bigger depending on capacity

Bigger

Equal

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

Sulphur dioxide

Carbon dioxide

Ammonia

Fluorine

Refrigeration & Air-Conditioning Practice Set-2

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