Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

2. 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

3. 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

4. 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

5. The lowest thermal diffusivity is of

Iron

Aluminium

Rubber

Lead

6. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Total heat lines

Temperature lines

Entropy lines

7. 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

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

None of the above

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

Simple evaporative air cooling system

All of these

Simple air cooling system

Bootstrap air cooling system

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

Bigger

Smaller

Equal

Smaller/bigger depending on capacity

10. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Is immaterial

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

Liquid

Wet vapour

Sub-cooled liquid

Saturated liquid

12. The dry bulb temperature during sensible heating of air

Increases

Decreases

Remains constant

None of these

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

Discharge pressure

Back pressure

Critical pressure

Suction pressure

14. 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

15. Carbon dioxide is

Non-flammable

Odourless

All of these

Colourless

16. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Receiver

Expansion valve

17. The optimum effective temperature for human comfort is

Same in winter and summer

Lower in winter than in summer

Not dependent on season

Higher in winter than in summer

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

Ammonia

Carbon dioxide

Fluorine

Sulphur dioxide

19. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is more than 1

Is equal to 1

20. Reducing suction pressure in refrigeration cycle

All of these

Lowers evaporation temperature

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

Page 3 of 4

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

Same

More/less depending on rating

Less

22. 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

23. Choose the correct statement

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

Pre-cooling and sub-cooling bf refrigerant are same

24. One ton of the refrigeration is

The standard unit used in refrigeration problems

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

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

Reduced to a value below its critical temperature

Equal to critical temperature

None of the above

Increased to a value above its critical temperature

26. 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

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

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

All of these

28. 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

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

Low weight per tonne of refrigeration

Higher coefficient of performance

High heat transfer rate

Low temperature at high altitudes

30. 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

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

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

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

None of these

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

33. 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

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

0.1 to 0.3 TR

3 to 5 TR

5 to 7 TR

1 to 3 TR

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

Less

Same

None of these

36. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of cooling medium

Of freezing zone

Of evaporator

37. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

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

Condenser

Expansion valve

Compressor

Evaporator

39. A one tonne refrigerating machine means that

One tonne refrigerant is used

One tonne is the total mass of machine

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

40. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

Refrigeration & Air-Conditioning Practice Set-2

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