Refrigeration & Air-Conditioning Practice Set-2

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

Condenser

Compressor

Evaporator

Expansion valve

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

None of the above

It is not affected by the moisture present in the air

The moisture present in it begins to condense

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

3. The COP of a domestic refrigerator

Is equal to 1

Is less than 1

Is more than 1

Depends upon the make

4. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

Increases

None of these

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

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

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

Low temperature at high altitudes

High heat transfer rate

Higher coefficient of performance

Low weight per tonne of refrigeration

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

Equal to critical temperature

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

8. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes gas

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

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

Between the second heat exchanger and the cooling turbine

10. 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

(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 - 1

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11. 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

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

Equalize

Increase

None of these

Reduce

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

Zero

Any value

As low as possible (3 to 11°C)

High, of the order of 25°

14. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

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

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

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

More

Less

Same

None of these

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

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

None of these

18. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Not dependent on season

Same in winter and summer

19. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Total heat lines

Temperature lines

Pressure lines

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

Liquid

Sub-cooled liquid

Wet vapour

Saturated liquid

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21. Formation of frost on evaporator in refrigerator

Is immaterial

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Increases heat transfer rate

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

0.1 to 0.3 TR

5 to 7 TR

3 to 5 TR

1 to 3 TR

23. 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

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

Smaller/bigger depending on capacity

Bigger

Smaller

Equal

25. Carbon dioxide is

All of these

Colourless

Odourless

Non-flammable

26. The higher temperature in vapour compression cycle occurs at

Evaporator

Receiver

Compressor discharge

Expansion valve

27. A one tonne refrigerating machine means that

One tonne refrigerant is used

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

28. The lowest thermal diffusivity is of

Aluminium

Rubber

Iron

Lead

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

Less

More/less depending on rating

More

Same

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

It reacts with copper and its alloys.

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

All of these

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

All of these

Simple evaporative air cooling system

Bootstrap air cooling system

Simple air cooling system

32. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

33. Choose the correct statement

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

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

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

Ammonia

Carbon dioxide

Sulphur dioxide

Fluorine

35. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Increases power required per ton of refrigeration

All of these

Lowers compressor capacity because vapour is lighter

36. During heating and dehumidification process, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

Discharge pressure

Back pressure

Critical pressure

Suction pressure

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

High latent heat of vaporisation

Tow specific heat of liquid

Higher critical temperature

High boiling point

39. 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

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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