Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. The lowest thermal diffusivity is of

Iron

Rubber

Aluminium

Lead

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

Back pressure

Suction pressure

Discharge pressure

Critical pressure

3. Formation of frost on evaporator in refrigerator

Is immaterial

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Increases heat transfer rate

4. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

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

None of the above

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

Liquid

Wet vapour

Saturated liquid

Sub-cooled liquid

7. The dry bulb temperature during sensible heating of air

Remains constant

Increases

Decreases

None of these

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

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

None of these

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

Higher critical temperature

High boiling point

Tow specific heat of liquid

High latent heat of vaporisation

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

Bootstrap air cooling system

All of these

Simple air cooling system

Simple evaporative air cooling system

Page 2 of 4

11. The COP of a domestic refrigerator

Is equal to 1

Is less than 1

Is more than 1

Depends upon the make

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

R-12

Carbon dioxide

Lithium bromide

Sulphur dioxide

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

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

None of these

14. 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

Before passing through the condenser

After passing through the condenser

15. 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

16. The higher temperature in vapour compression cycle occurs at

Receiver

Evaporator

Expansion valve

Compressor discharge

17. 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

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

Equal

Bigger

Smaller

Smaller/bigger depending on capacity

19. 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

20. Carbon dioxide is

Non-flammable

All of these

Odourless

Colourless

Page 3 of 4

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

Zero

Any value

As low as possible (3 to 11°C)

High, of the order of 25°

22. During heating and dehumidification process, dry bulb temperature

Remains constant

Increases

Decreases

None of these

23. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Critical pressure of refrigerant

Much above critical pressure

24. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Pressure lines

Entropy lines

25. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

26. 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

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

It requires large displacement per TR compared to fluoro carbons.

It is toxic to mucous membranes.

It reacts with copper and its alloys.

All of these

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

Reduce

Equalize

Increase

None of these

29. 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

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

More

More/less depending on rating

Less

Same

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

Can be lower or higher than that of the entering air

Is lower than that of the entering air

None of the above

Is higher than that of the entering air

33. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes gas

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

Expansion valve

Condenser

Compressor

Evaporator

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

None of the above

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

Equal to critical temperature

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

Fluorine

Ammonia

Sulphur dioxide

Carbon dioxide

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

High heat transfer rate

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

38. 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 + 2

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

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

39. 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

Ammonia vapour is driven out of solution

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

More

Same

None of these

Less

Refrigeration & Air-Conditioning Practice Set-2

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