Refrigeration & Air-Conditioning Practice Set-2

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1. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

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

More

Less

Same

None of these

3. The dry bulb temperature during sensible heating of air

None of these

Remains constant

Decreases

Increases

4. One ton of the refrigeration is

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

The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

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

Increased to a value above its critical temperature

Equal to critical temperature

None of the above

Reduced to a value below its critical temperature

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

Ammonia

Carbon dioxide

Fluorine

Sulphur dioxide

8. 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

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

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

None of these

10. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Pressure lines

Temperature lines

Entropy lines

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11. 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 + 1

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

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

12. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Depends upon the make

Is less than 1

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

High, of the order of 25°

Zero

Any value

As low as possible (3 to 11°C)

14. 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

Same

Less

More

15. 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

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

Smaller

Equal

Bigger

Smaller/bigger depending on capacity

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

All of these

Simple evaporative air cooling system

Simple air cooling system

Bootstrap air cooling system

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

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

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

Expansion valve

Condenser

Evaporator

Compressor

20. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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

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21. Choose the correct statement

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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

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

Sulphur dioxide

R-12

Carbon dioxide

Lithium bromide

23. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

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

Liquid

Sub-cooled liquid

Wet vapour

Saturated liquid

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

None of the above

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

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

Discharge pressure

Critical pressure

Back pressure

Suction pressure

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

0.1 to 0.3 TR

1 to 3 TR

5 to 7 TR

3 to 5 TR

28. 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

29. The optimum effective temperature for human comfort is

Higher in winter than in summer

Not dependent on season

Same in winter and summer

Lower in winter than in summer

30. 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

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31. Carbon dioxide is

All of these

Colourless

Non-flammable

Odourless

32. Formation of frost on evaporator in refrigerator

Is immaterial

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

33. The lowest thermal diffusivity is of

Rubber

Lead

Iron

Aluminium

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

High heat transfer rate

Low temperature at high altitudes

Low weight per tonne of refrigeration

Higher coefficient of performance

35. During heating and dehumidification process, dry bulb temperature

Decreases

None of these

Increases

Remains constant

36. Reducing suction pressure in refrigeration cycle

All of these

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

Lowers evaporation temperature

37. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes solid

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

Increase

None of these

Equalize

Reduce

39. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Receiver

Expansion valve

40. 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.

Refrigeration & Air-Conditioning Practice Set-2

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