Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Expansion valve

Condenser

Compressor

Evaporator

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

Discharge pressure

Critical pressure

Suction pressure

Back pressure

3. 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.

All of these

It reacts with copper and its alloys.

4. One ton of the refrigeration is

The standard unit used in refrigeration problems

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

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

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

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

Between the second heat exchanger and the cooling turbine

6. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Is equal to 1

Depends upon the make

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

Any value

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

8. The higher temperature in vapour compression cycle occurs at

Receiver

Compressor discharge

Evaporator

Expansion valve

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

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

Increased to a value above its critical temperature

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

Equal

Smaller

Smaller/bigger depending on capacity

Bigger

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11. 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

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

None of the above

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

13. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

All of these

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

14. 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

15. The optimum effective temperature for human comfort is

Not dependent on season

Higher in winter than in summer

Same in winter and summer

Lower in winter than in summer

16. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Pressure lines

Entropy lines

Total heat lines

17. 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

18. During heating and dehumidification process, dry bulb temperature

Decreases

None of these

Remains constant

Increases

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

20. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes vapour

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

Less

More

More/less depending on rating

Same

22. The dry bulb temperature during sensible heating of air

None of these

Increases

Decreases

Remains constant

23. 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

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

Sub-cooled liquid

Liquid

Saturated liquid

Wet vapour

25. 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 + 2

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

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

Lithium bromide

R-12

Sulphur dioxide

Carbon dioxide

27. 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

28. Carbon dioxide is

All of these

Odourless

Non-flammable

Colourless

29. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

One tonne is the total mass of machine

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

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

5 to 7 TR

1 to 3 TR

0.1 to 0.3 TR

3 to 5 TR

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

Higher coefficient of performance

Low weight per tonne of refrigeration

Low temperature at high altitudes

High heat transfer rate

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

Low pressure vapour refrigerant

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

33. 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

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

Carbon dioxide

Fluorine

Sulphur dioxide

Ammonia

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

More

Less

None of these

Same

36. The lowest thermal diffusivity is of

Rubber

Lead

Iron

Aluminium

37. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

38. 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

39. 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

Reduce

Equalize

Increase

40. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

Refrigeration & Air-Conditioning Practice Set-2

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