Refrigeration & Air-Conditioning Practice Set-2

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1. 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.

It requires large displacement per TR compared to fluoro carbons.

All of these

2. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of evaporator

At which refrigerant gas becomes liquid

Of freezing zone

3. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes vapour

4. 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

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

Any value

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

6. The lowest thermal diffusivity is of

Rubber

Iron

Aluminium

Lead

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

Condenser

Evaporator

Expansion valve

Compressor

8. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Receiver

Evaporator

9. 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

10. The COP of a domestic refrigerator

Depends upon the make

Is more than 1

Is equal to 1

Is less than 1

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11. 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

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

Ammonia

Carbon dioxide

Sulphur dioxide

Fluorine

13. 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 standard unit used in refrigeration problems

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

The cooling effect produced by melting 1 ton of ice

14. Choose the correct statement

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

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

15. 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

16. 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

17. The optimum effective temperature for human comfort is

Lower in winter than in summer

Not dependent on season

Same in winter and summer

Higher in winter than in summer

18. 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 refrigerant is used

One tonne is the total mass of machine

One tonne of water can be converted into ice

19. 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

20. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

Remains constant

None of these

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21. Carbon dioxide is

Non-flammable

Colourless

All of these

Odourless

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

More

None of these

Less

Same

23. 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

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

Suction pressure

Discharge pressure

Critical pressure

Back pressure

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

All of these

Simple air cooling system

Simple evaporative air cooling system

Bootstrap air cooling system

26. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Pressure lines

Total heat lines

Temperature lines

27. 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

Same

More

28. 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

29. 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

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

Saturated liquid

Wet vapour

Sub-cooled liquid

Liquid

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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. 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

33. 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

34. 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 first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

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

Wet vapour region

Superheated vapour region

None of these

Sub-cooled liquid region

36. 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

37. The dry bulb temperature during sensible heating of air

Increases

None of these

Remains constant

Decreases

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

Bigger

Smaller/bigger depending on capacity

Smaller

Equal

39. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

None of the above

Refrigeration & Air-Conditioning Practice Set-2

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