Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Total heat lines

Temperature lines

Pressure lines

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

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

None of these

Low pressure vapour refrigerant

3. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

Can be avoided by proper design

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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

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

Equalize

Increase

None of these

Reduce

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

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

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

Expansion valve

Compressor

Condenser

Evaporator

8. Reducing suction pressure in refrigeration cycle

All of these

Increases power required per ton of refrigeration

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

9. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

Of cooling medium

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

Lithium bromide

Carbon dioxide

R-12

Sulphur dioxide

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11. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

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

Low temperature at high altitudes

High heat transfer rate

Higher coefficient of performance

Low weight per tonne of refrigeration

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

Fluorine

Sulphur dioxide

Ammonia

Carbon dioxide

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

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

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

None of these

More

Same

Less

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

Superheated vapour region

Wet vapour region

Sub-cooled liquid region

None of these

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

Any value

As low as possible (3 to 11°C)

High, of the order of 25°

Zero

18. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Compressor discharge

Receiver

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

Smaller

Smaller/bigger depending on capacity

Bigger

Equal

20. The dry bulb temperature during sensible heating of air

None of these

Decreases

Remains constant

Increases

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21. 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

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

Wet vapour

Saturated liquid

Liquid

Sub-cooled liquid

23. The optimum effective temperature for human comfort is

Same in winter and summer

Lower in winter than in summer

Higher in winter than in summer

Not dependent on season

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

More

Same

More/less depending on rating

Less

25. During heating and dehumidification process, dry bulb temperature

Increases

Remains constant

None of these

Decreases

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

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

5 to 7 TR

27. 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

The moisture present in it begins to condense

None of the above

It is not affected by the moisture present in the air

28. Choose the correct statement

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

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

29. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

30. 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 standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

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

Tow specific heat of liquid

Higher critical temperature

High latent heat of vaporisation

High boiling point

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

Bootstrap air cooling system

Simple air cooling system

Simple evaporative air cooling system

All of these

33. The lowest thermal diffusivity is of

Rubber

Iron

Aluminium

Lead

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

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

35. Carbon dioxide is

Odourless

Non-flammable

Colourless

All of these

36. 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 + 1

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

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

Back pressure

Suction pressure

Discharge pressure

Critical pressure

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

Is lower than that of the entering air

Is higher than that of the entering air

None of the above

Can be lower or higher than that of the entering air

39. The COP of a domestic refrigerator

Is less than 1

Is equal to 1

Is more than 1

Depends upon the make

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

It is toxic to mucous membranes.

It reacts with copper and its alloys.

All of these

It requires large displacement per TR compared to fluoro carbons.

Refrigeration & Air-Conditioning Practice Set-2

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