Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

5 to 7 TR

3 to 5 TR

1 to 3 TR

0.1 to 0.3 TR

2. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

3. 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

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

Ammonia

Sulphur dioxide

Carbon dioxide

Fluorine

5. 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

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

It is toxic to mucous membranes.

All of these

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

7. 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

8. The optimum effective temperature for human comfort is

Lower in winter than in summer

Same in winter and summer

Not dependent on season

Higher in winter than in summer

9. 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

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

Condenser

Evaporator

Compressor

Expansion valve

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11. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of evaporator

Of freezing zone

At which refrigerant gas becomes liquid

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

All of these

Bootstrap air cooling system

Simple air cooling system

Simple evaporative air cooling system

13. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Is immaterial

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

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

Sub-cooled liquid region

None of these

Superheated vapour region

Wet vapour region

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

Liquid

Sub-cooled liquid

Wet vapour

Saturated liquid

16. 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

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

Equalize

Reduce

Increase

None of these

18. Choose the correct statement

A refrigerant should have low latent heat

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

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

Same

More

More/less depending on rating

Less

20. 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

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21. 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

22. 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

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

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

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

Smaller

Equal

Bigger

Smaller/bigger depending on capacity

24. The dry bulb temperature during sensible heating of air

Decreases

Increases

None of these

Remains constant

25. Carbon dioxide is

Colourless

Odourless

Non-flammable

All of these

26. The lowest thermal diffusivity is of

Rubber

Lead

Aluminium

Iron

27. 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

28. During heating and dehumidification process, dry bulb temperature

None of these

Increases

Remains constant

Decreases

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

Critical pressure

Suction pressure

Back pressure

Discharge pressure

30. 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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31. Pick up the wrong statement. A refrigerant should have

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

High boiling point

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

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

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

None of the above

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

Low weight per tonne of refrigeration

Higher coefficient of performance

High heat transfer rate

Low temperature at high altitudes

35. The COP of a domestic refrigerator

Depends upon the make

Is equal to 1

Is more than 1

Is less than 1

36. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Pressure lines

Entropy lines

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

None of these

Same

More

Less

38. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Critical pressure of refrigerant

Much below critical pressure

39. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Receiver

Expansion valve

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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