Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

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

Evaporator

Compressor

Condenser

Expansion valve

2. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Same in winter and summer

Not dependent on season

3. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

Near critical pressure

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

Lithium bromide

R-12

Sulphur dioxide

Carbon dioxide

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

Carbon dioxide

Fluorine

Ammonia

Sulphur dioxide

6. 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

7. One ton of the refrigeration is

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

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

8. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Evaporator

Expansion valve

9. The COP of a domestic refrigerator

Is equal to 1

Is less than 1

Is more than 1

Depends upon the make

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

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

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11. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

Of cooling medium

12. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Entropy lines

Pressure lines

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

Increase

Equalize

Reduce

None of these

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

High boiling point

Tow specific heat of liquid

Higher critical temperature

High latent heat of vaporisation

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

Saturated liquid

Liquid

Sub-cooled liquid

Wet vapour

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

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

Low weight per tonne of refrigeration

17. 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 + 2

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

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

All of these

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

It is toxic to mucous membranes.

19. 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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

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

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

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21. The dry bulb temperature during sensible heating of air

Remains constant

Increases

Decreases

None of these

22. 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 is driven out of solution

Ammonia vapour goes into solution

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

None of these

Less

Same

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

As low as possible (3 to 11°C)

High, of the order of 25°

Any value

Zero

25. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Is immaterial

26. Choose the correct statement

Pre-cooling and sub-cooling bf 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

Superheat and sensible heat of a refrigerant are same

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

Smaller/bigger depending on capacity

Equal

Smaller

Bigger

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

Discharge pressure

Back pressure

Suction pressure

Critical pressure

29. During heating and dehumidification process, dry bulb temperature

None of these

Increases

Remains constant

Decreases

30. 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

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31. 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

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

Bootstrap air cooling system

All of these

Simple evaporative air cooling system

Simple air cooling system

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

Wet vapour region

Sub-cooled liquid region

None of these

Superheated vapour region

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. The lowest thermal diffusivity is of

Rubber

Aluminium

Lead

Iron

36. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid will remain liquid

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

1 to 3 TR

0.1 to 0.3 TR

5 to 7 TR

3 to 5 TR

38. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

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 is the total mass of machine

One tonne refrigerant is used

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

Is higher than that of the entering air

Can be lower or higher than that of the entering air

Is lower than that of the entering air

None of the above

40. Carbon dioxide is

Odourless

All of these

Colourless

Non-flammable

Refrigeration & Air-Conditioning Practice Set-2

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