Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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

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

Discharge pressure

Critical pressure

Suction pressure

Back pressure

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

4. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Receiver

Compressor discharge

5. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

6. 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

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

More

Less

Same

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

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

Low pressure vapour refrigerant

9. 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

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

Liquid

Sub-cooled liquid

Saturated liquid

Wet vapour

Page 2 of 4

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

Same

More

Less

None of these

12. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

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

Higher coefficient of performance

Low weight per tonne of refrigeration

High heat transfer rate

Low temperature at high altitudes

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

Sulphur dioxide

Carbon dioxide

Lithium bromide

R-12

15. One ton of the refrigeration is

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

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

The standard unit used in refrigeration problems

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

Evaporator

Expansion valve

Compressor

Condenser

17. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

Is immaterial

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

Is lower than that of the entering air

None of the above

Can be lower or higher than that of the entering air

Is higher than that of the entering air

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

3 to 5 TR

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

20. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Critical pressure of refrigerant

Much above critical pressure

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21. Carbon dioxide is

Non-flammable

All of these

Odourless

Colourless

22. The COP of a domestic refrigerator

Is more than 1

Is less than 1

Is equal to 1

Depends upon the make

23. 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

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

Zero

As low as possible (3 to 11°C)

High, of the order of 25°

Any value

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

Sulphur dioxide

Fluorine

Carbon dioxide

Ammonia

26. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes solid

Above which liquid becomes vapour

27. The optimum effective temperature for human comfort is

Not dependent on season

Same in winter and summer

Lower in winter than in summer

Higher in winter than in summer

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

High latent heat of vaporisation

Higher critical temperature

High boiling point

Tow specific heat of liquid

29. The lowest thermal diffusivity is of

Iron

Aluminium

Lead

Rubber

30. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

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

Increase

Equalize

None of these

Reduce

32. The dry bulb temperature during sensible heating of air

Increases

Remains constant

None of these

Decreases

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

None of the above

Increased to a value above its critical temperature

Equal to critical temperature

Reduced to a value below its critical temperature

34. 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

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

All of these

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

It is toxic to mucous membranes.

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

Smaller

Bigger

Smaller/bigger depending on capacity

Equal

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

Between the second heat exchanger and the cooling turbine

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

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

Simple air cooling system

Bootstrap air cooling system

All of these

Simple evaporative air cooling system

39. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Temperature lines

Pressure lines

Total heat lines

40. Choose the correct statement

A refrigerant should have low latent heat

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

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

Refrigeration & Air-Conditioning Practice Set-2

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