Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

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

All of these

Simple air cooling system

Bootstrap air cooling system

Simple evaporative air cooling system

3. 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

4. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Compressor discharge

Receiver

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

6. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

Of freezing zone

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

More/less depending on rating

Less

More

Same

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

Equal

Smaller

Smaller/bigger depending on capacity

Bigger

9. 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

10. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

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 is the total mass of machine

Page 2 of 4

11. 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

12. 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

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

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

Low weight per tonne of refrigeration

14. 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

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

Reduce

None of these

Increase

Equalize

16. The optimum effective temperature for human comfort is

Same in winter and summer

Not dependent on season

Lower in winter than in summer

Higher in winter than in summer

17. 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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

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

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

19. Carbon dioxide is

All of these

Odourless

Non-flammable

Colourless

20. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Depends upon the make

Is equal to 1

Page 3 of 4

21. 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

It is not affected by the moisture present in the air

None of the above

The moisture present in it begins to condense

22. 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

23. 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

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

Critical pressure

Discharge pressure

Suction pressure

Back pressure

25. The lowest thermal diffusivity is of

Rubber

Iron

Lead

Aluminium

26. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

27. One ton of the refrigeration is

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 refrigeration effect to produce 1 ton of ice at NTP conditions

The standard unit used in refrigeration problems

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

Evaporator

Condenser

Expansion valve

Compressor

29. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

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

As low as possible (3 to 11°C)

High, of the order of 25°

Any value

Zero

Page 4 of 4

31. The dry bulb temperature during sensible heating of air

None of these

Remains constant

Decreases

Increases

32. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Pressure lines

Total heat lines

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

Saturated liquid

Liquid

Sub-cooled liquid

Wet vapour

34. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

35. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Sulphur dioxide

Fluorine

Ammonia

Carbon dioxide

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

5 to 7 TR

3 to 5 TR

1 to 3 TR

0.1 to 0.3 TR

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

More

Same

Less

None of these

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

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

Between the secondary compressor and the second heat exchanger

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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