Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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

Higher coefficient of performance

Low temperature at high altitudes

Low weight per tonne of refrigeration

High heat transfer rate

2. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Much above critical pressure

Near critical pressure

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

Sub-cooled liquid

Liquid

Wet vapour

Saturated liquid

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

None of the above

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

5. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

Remains constant

None of these

6. Choose the correct statement

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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

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

Sulphur dioxide

Lithium bromide

Carbon dioxide

R-12

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

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

None of these

9. The optimum effective temperature for human comfort is

Lower in winter than in summer

Same in winter and summer

Not dependent on season

Higher in winter than in summer

10. The dry bulb temperature during sensible heating of air

None of these

Remains constant

Increases

Decreases

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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 - 1

(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 + 2

12. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Is immaterial

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

13. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid becomes gas

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

High latent heat of vaporisation

Higher critical temperature

High boiling point

Tow specific heat of liquid

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

None of the above

Equal to critical temperature

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

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

Bootstrap air cooling system

Simple evaporative air cooling system

Simple air cooling system

All of these

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

Same

Less

More/less depending on rating

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

Equal

Smaller

Smaller/bigger depending on capacity

Bigger

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

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21. The evolution of heat of solution takes place in ammonia absorption plant when

Weak solution mixes with strong solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

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

Equalize

Reduce

None of these

Increase

23. The lowest thermal diffusivity is of

Aluminium

Iron

Lead

Rubber

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

Ammonia

Carbon dioxide

Sulphur dioxide

Fluorine

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

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

26. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne of water can be converted into ice

One tonne refrigerant is used

One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

27. The higher temperature in vapour compression cycle occurs at

Expansion valve

Receiver

Evaporator

Compressor discharge

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

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

High pressure liquid refrigerant

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

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

It is toxic to mucous membranes.

All of these

30. 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

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31. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is less than 1

Is equal to 1

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

None of these

Less

Same

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

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

Between the combustion chamber and the first heat exchanger

34. Carbon dioxide is

All of these

Non-flammable

Colourless

Odourless

35. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

All of these

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

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

Evaporator

Condenser

Compressor

Expansion valve

37. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Pressure lines

Entropy lines

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

Is lower than that of the entering air

Is higher than that of the entering air

Can be lower or higher than that of the entering air

None of the above

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

Discharge pressure

Critical pressure

Suction pressure

Back pressure

40. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Refrigeration & Air-Conditioning Practice Set-2

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