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 refrigerant is used

One tonne is the total mass of machine

One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

2. 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 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

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

Critical pressure

Discharge pressure

Suction pressure

Back pressure

4. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Same in winter and summer

Not dependent on season

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

None of the above

Is higher than that of the entering air

Can be lower or higher than that of the entering air

Is lower than that of the entering air

6. 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

7. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

8. The lowest thermal diffusivity is of

Iron

Lead

Rubber

Aluminium

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

It reacts with copper and its alloys.

It is toxic to mucous membranes.

All of these

It requires large displacement per TR compared to fluoro carbons.

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

3 to 5 TR

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

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

Smaller/bigger depending on capacity

Smaller

Bigger

Equal

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

Low temperature at high altitudes

High heat transfer rate

Low weight per tonne of refrigeration

Higher coefficient of performance

13. 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

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

None of these

15. 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

None of the above

Equal to critical temperature

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

Condenser

Expansion valve

Evaporator

Compressor

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

Simple evaporative air cooling system

Bootstrap air cooling system

All of these

Simple air cooling system

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

Ammonia

Fluorine

Sulphur dioxide

Carbon dioxide

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

Less

None of these

More

Same

20. Carbon dioxide is

Non-flammable

All of these

Colourless

Odourless

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21. Choose the correct statement

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

If operating temperature of system is low, then refrigerant with low boiling point should be used

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

Carbon dioxide

R-12

Lithium bromide

Sulphur dioxide

23. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

24. 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

25. 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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

26. 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

27. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Total heat lines

Temperature lines

Pressure lines

28. 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

29. 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

30. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

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

Between the second heat exchanger and the cooling turbine

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

32. 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

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

Less

More/less depending on rating

More

Same

34. The higher temperature in vapour compression cycle occurs at

Expansion valve

Receiver

Evaporator

Compressor discharge

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

High boiling point

High latent heat of vaporisation

Higher critical temperature

Tow specific heat of liquid

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

Saturated liquid

Liquid

Wet vapour

Sub-cooled liquid

37. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid becomes gas

38. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is less than 1

Is more than 1

39. The dry bulb temperature during sensible heating of air

Decreases

None of these

Increases

Remains constant

40. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

Refrigeration & Air-Conditioning Practice Set-2

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