Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. 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

2. The optimum effective temperature for human comfort is

Higher in winter than in summer

Same in winter and summer

Not dependent on season

Lower in winter than in summer

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

High, of the order of 25°

As low as possible (3 to 11°C)

Zero

Any value

4. Formation of frost on evaporator in refrigerator

Is immaterial

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

5. 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 + 2

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

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

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

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

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

Liquid

Wet vapour

Sub-cooled liquid

Saturated liquid

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

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

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

High heat transfer rate

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

10. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

One tonne is the total mass of machine

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

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11. The higher temperature in vapour compression cycle occurs at

Receiver

Evaporator

Expansion valve

Compressor discharge

12. The lowest thermal diffusivity is of

Iron

Rubber

Lead

Aluminium

13. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is less than 1

Is more than 1

14. Choose the correct statement

Superheat and sensible heat of a refrigerant are same

If operating temperature of system is low, then refrigerant with low boiling point should be used

Pre-cooling and sub-cooling bf refrigerant are same

A refrigerant should have low latent heat

15. 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.

All of these

It is toxic to mucous membranes.

16. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Pressure lines

Temperature lines

Total heat lines

17. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

18. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

Remains constant

None of these

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

Sulphur dioxide

Carbon dioxide

Lithium bromide

R-12

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

Condenser

Expansion valve

Evaporator

Compressor

Page 3 of 4

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

Equalize

Increase

Reduce

None of these

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

None of these

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

23. Carbon dioxide is

Odourless

Non-flammable

All of these

Colourless

24. 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

25. The dry bulb temperature during sensible heating of air

Remains constant

Increases

None of these

Decreases

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

None of the above

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

27. 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

28. 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

29. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

All of these

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

30. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

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31. 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

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

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

More/less depending on rating

Less

Same

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

None of these

Low pressure vapour refrigerant

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

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

Same

None of these

Less

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

Fluorine

Ammonia

Carbon dioxide

Sulphur dioxide

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

Reduced to a value below its critical temperature

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

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

Bigger

Smaller/bigger depending on capacity

Equal

Smaller

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

Back pressure

Discharge pressure

Suction pressure

Critical pressure

40. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes vapour

Refrigeration & Air-Conditioning Practice Set-2

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