Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

2. 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

3. 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

4. Choose the correct statement

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

A refrigerant should have low latent heat

5. 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

6. During heating and dehumidification process, dry bulb temperature

Remains constant

Decreases

Increases

None of these

7. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

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

Same

More/less depending on rating

More

Less

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

Simple air cooling system

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

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

Smaller/bigger depending on capacity

Equal

Smaller

Bigger

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11. The lowest thermal diffusivity is of

Lead

Rubber

Iron

Aluminium

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

13. A one tonne refrigerating machine means that

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 of water can be converted into ice

One tonne refrigerant is used

One tonne is the total mass of machine

14. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

All of these

Lowers evaporation temperature

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

Can be lower or higher than that of the entering air

None of the above

Is higher than that of the entering air

Is lower than that of the entering air

16. Formation of frost on evaporator in refrigerator

Is immaterial

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

17. The higher temperature in vapour compression cycle occurs at

Expansion valve

Evaporator

Compressor discharge

Receiver

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

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

Equal to critical temperature

19. The dry bulb temperature during sensible heating of air

Decreases

Increases

None of these

Remains constant

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

Compressor

Evaporator

Condenser

Expansion valve

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21. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

22. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Pressure lines

Temperature lines

Entropy lines

23. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

Much above critical pressure

24. The optimum effective temperature for human comfort is

Same in winter and summer

Higher in winter than in summer

Not dependent on season

Lower in winter than in summer

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

Low weight per tonne of refrigeration

Low temperature at high altitudes

High heat transfer rate

Higher coefficient of performance

26. 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 refrigeration effect to produce 1 ton of ice at NTP conditions

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

27. 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

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

None of these

Same

Less

More

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

Critical pressure

Suction pressure

Discharge pressure

Back pressure

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

Liquid

Sub-cooled liquid

Wet vapour

Saturated liquid

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31. 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°

Zero

Any value

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

High boiling point

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

33. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Is equal to 1

Depends upon the make

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

Carbon dioxide

Lithium bromide

R-12

Sulphur dioxide

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

None of these

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

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

Fluorine

Carbon dioxide

Sulphur dioxide

Ammonia

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

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

38. 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.

39. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

40. 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 + 2

(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 + 1

Refrigeration & Air-Conditioning Practice Set-2

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