Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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

Fluorine

Carbon dioxide

Sulphur dioxide

Ammonia

2. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Not dependent on season

Same in winter and summer

3. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

Any value

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

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

6. The lowest thermal diffusivity is of

Lead

Aluminium

Rubber

Iron

7. 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 of water can be converted into ice

One tonne is the total mass of machine

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

Can be lower or higher than that of the entering air

Is lower than that of the entering air

Is higher than that of the entering air

None of the above

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

Equal

Smaller/bigger depending on capacity

Bigger

Smaller

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

3 to 5 TR

1 to 3 TR

0.1 to 0.3 TR

5 to 7 TR

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11. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

12. The higher temperature in vapour compression cycle occurs at

Evaporator

Receiver

Compressor discharge

Expansion valve

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

Less

None of these

Same

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

Pre-cooling and sub-cooling bf refrigerant are same

A refrigerant should have low latent heat

15. 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

16. The dry bulb temperature during sensible heating of air

Remains constant

Increases

Decreases

None of these

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

Critical pressure

Back pressure

Discharge pressure

Suction pressure

18. 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

19. 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

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

It is not affected by the moisture present in the air

20. 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 - 1

(C.O.P.)_P = (C.O.P.)_R + 1

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

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

Condenser

Expansion valve

Evaporator

Compressor

22. Carbon dioxide is

All of these

Odourless

Colourless

Non-flammable

23. 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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

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

Reduce

Increase

None of these

Equalize

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

Lithium bromide

R-12

Carbon dioxide

Sulphur dioxide

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

Less

Same

More/less depending on rating

27. During heating and dehumidification process, dry bulb temperature

Remains constant

None of these

Decreases

Increases

28. 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

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

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

30. 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

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

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

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

All of these

Simple evaporative air cooling system

Simple air cooling system

Bootstrap air cooling system

33. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Temperature lines

Total heat lines

Pressure lines

34. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is more than 1

Is equal to 1

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

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

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

Wet vapour region

None of these

Sub-cooled liquid region

Superheated vapour region

37. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

38. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid will remain liquid

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

High latent heat of vaporisation

Tow specific heat of liquid

High boiling point

Higher critical temperature

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

Wet vapour

Liquid

Sub-cooled liquid

Saturated liquid

Refrigeration & Air-Conditioning Practice Set-2

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