Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

High latent heat of vaporisation

High boiling point

Higher critical temperature

Tow specific heat of liquid

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

Can be lower or higher than that of the entering air

Is higher than that of the entering air

Is lower than that of the entering air

None of the above

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

Zero

Any value

High, of the order of 25°

As low as possible (3 to 11°C)

4. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Not dependent on season

Same in winter and summer

5. One ton of the refrigeration is

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 cooling effect produced by melting 1 ton of ice

The standard unit used in refrigeration problems

6. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid will remain liquid

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

Simple evaporative air cooling system

All of these

Simple air cooling system

Bootstrap air cooling system

8. A one tonne refrigerating machine means that

One tonne refrigerant is used

One tonne is the total mass of machine

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

9. During heating and dehumidification process, dry bulb temperature

Increases

None of these

Remains constant

Decreases

10. Condensing temperature in a refrigerator is the temperature

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

Of freezing zone

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11. 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

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

More

Less

More/less depending on rating

Same

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

Equal to critical temperature

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

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

Reduce

Increase

Equalize

None of these

15. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is less than 1

Is equal to 1

16. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

Increases

None of these

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

None of these

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

18. The lowest thermal diffusivity is of

Iron

Lead

Rubber

Aluminium

19. Choose the correct statement

A refrigerant should have low latent heat

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

Pre-cooling and sub-cooling bf refrigerant are same

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

High heat transfer rate

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

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

More

Less

None of these

Same

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

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

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

Sub-cooled liquid

Liquid

Wet vapour

Saturated liquid

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

Back pressure

Suction pressure

Discharge pressure

Critical pressure

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

26. 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 combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

27. The higher temperature in vapour compression cycle occurs at

Expansion valve

Evaporator

Receiver

Compressor discharge

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

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

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

Smaller/bigger depending on capacity

Bigger

Equal

Smaller

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

Carbon dioxide

Sulphur dioxide

Lithium bromide

R-12

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31. 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 + 2

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

32. 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

33. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

Lowers evaporation temperature

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

Ammonia

Carbon dioxide

Sulphur dioxide

Fluorine

35. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Critical pressure of refrigerant

Much above critical pressure

36. Carbon dioxide is

All of these

Non-flammable

Odourless

Colourless

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

Evaporator

Compressor

Expansion valve

Condenser

38. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Is immaterial

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

39. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Total heat lines

Entropy lines

Temperature lines

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

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

Low pressure vapour refrigerant

None of these

Refrigeration & Air-Conditioning Practice Set-2

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