Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Pressure lines

Total heat lines

Temperature lines

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

None of the above

Can be lower or higher than that of the entering air

Is lower than that of the entering air

Is higher than that of the entering air

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

High, of the order of 25°

Any value

Zero

As low as possible (3 to 11°C)

4. 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 + 2

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

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

5. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

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

Same

None of these

More

Less

7. 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

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

Low weight per tonne of refrigeration

High heat transfer rate

Higher coefficient of performance

Low temperature at high altitudes

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

Same

Less

More

More/less depending on rating

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

Sub-cooled liquid region

Superheated vapour region

Wet vapour region

None of these

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

Carbon dioxide

Sulphur dioxide

R-12

Lithium bromide

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

Ammonia

Sulphur dioxide

Fluorine

Carbon dioxide

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

Tow specific heat of liquid

High latent heat of vaporisation

High boiling point

Higher critical temperature

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

Expansion valve

Evaporator

Condenser

Compressor

15. The dry bulb temperature during sensible heating of air

Remains constant

None of these

Increases

Decreases

16. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Increases power required per ton of refrigeration

All of these

Lowers compressor capacity because vapour is lighter

17. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Not dependent on season

Same in winter and summer

18. 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

19. 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 entering the expansion valve

Before passing through the condenser

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

0.1 to 0.3 TR

3 to 5 TR

1 to 3 TR

5 to 7 TR

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21. The lowest thermal diffusivity is of

Lead

Iron

Rubber

Aluminium

22. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

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

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

All of these

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

Equal to critical temperature

Reduced to a value below its critical temperature

None of the above

Increased to a value above its critical temperature

25. One ton of the refrigeration is

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

The cooling effect produced by melting 1 ton of ice

The standard unit used in refrigeration problems

The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

26. Formation of frost on evaporator in refrigerator

Is immaterial

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

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

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

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

Simple evaporative air cooling system

Bootstrap air cooling system

Simple air cooling system

All of these

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

Low pressure vapour refrigerant

None of these

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

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

Bigger

Smaller

Equal

Smaller/bigger depending on capacity

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31. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Receiver

Expansion valve

32. 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

33. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes vapour

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

Critical pressure

Back pressure

Discharge pressure

Suction pressure

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

It is not affected by the moisture present in the air

None of the above

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

The moisture present in it begins to condense

36. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is equal to 1

Is more than 1

37. Carbon dioxide is

Odourless

Colourless

Non-flammable

All of these

38. A one tonne refrigerating machine means that

One tonne refrigerant is used

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 of water can be converted into ice

One tonne is the total mass of machine

39. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

None of these

Remains constant

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

Sub-cooled liquid

Wet vapour

Saturated liquid

Liquid

Refrigeration & Air-Conditioning Practice Set-2

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