Refrigeration & Air-Conditioning Practice Set-2

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

Sulphur dioxide

Ammonia

Carbon dioxide

Fluorine

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

Reduced to a value below its critical temperature

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

3. Carbon dioxide is

All of these

Non-flammable

Odourless

Colourless

4. The COP of a domestic refrigerator

Is equal to 1

Is less than 1

Depends upon the make

Is more than 1

5. Choose the correct statement

Superheat and sensible heat of a refrigerant are same

A refrigerant should have low latent heat

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

6. 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

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

None of these

Same

More

Less

8. The higher temperature in vapour compression cycle occurs at

Expansion valve

Receiver

Compressor discharge

Evaporator

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

Low weight per tonne of refrigeration

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

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

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

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

Less

More

Same

More/less depending on rating

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

Condenser

Compressor

Expansion valve

Evaporator

13. 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 - 1

(C.O.P.)_P = (C.O.P.)_R + 2

14. 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

Equalize

Increase

Reduce

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

High, of the order of 25°

Any value

As low as possible (3 to 11°C)

Zero

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

Saturated liquid

Liquid

Wet vapour

Sub-cooled liquid

17. The lowest thermal diffusivity is of

Lead

Rubber

Aluminium

Iron

18. During heating and dehumidification process, dry bulb temperature

None of these

Decreases

Remains constant

Increases

19. 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

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

Bigger

Smaller/bigger depending on capacity

Smaller

Equal

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

5 to 7 TR

3 to 5 TR

0.1 to 0.3 TR

1 to 3 TR

22. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

Of freezing zone

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

It is toxic to mucous membranes.

All of these

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

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

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Is higher than that of the entering air

None of the above

25. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Pressure lines

Temperature lines

Total heat lines

26. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

The standard unit used in refrigeration problems

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

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

High pressure liquid refrigerant

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

28. Reducing suction pressure in refrigeration cycle

All of these

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

29. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Much below critical pressure

Near critical pressure

Critical pressure of refrigerant

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

Simple air cooling system

All of these

Bootstrap air cooling system

Simple evaporative air cooling system

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31. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

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

High boiling point

Tow specific heat of liquid

High latent heat of vaporisation

Higher critical temperature

33. 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

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

Back pressure

Discharge pressure

Critical pressure

Suction pressure

35. 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

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

Wet vapour region

None of these

Superheated vapour region

Sub-cooled liquid region

37. The dry bulb temperature during sensible heating of air

None of these

Decreases

Increases

Remains constant

38. 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

39. 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

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

The moisture present in it begins to condense

None of the above

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

It is not affected by the moisture present in the air

Refrigeration & Air-Conditioning Practice Set-2

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