Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

2. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

3. The COP of a domestic refrigerator

Is less than 1

Is equal to 1

Depends upon the make

Is more than 1

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

More

Less

Same

None of these

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

Compressor

Condenser

Expansion valve

Evaporator

6. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid becomes vapour

7. 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

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

9. 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

More

10. 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

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

Zero

As low as possible (3 to 11°C)

Any value

High, of the order of 25°

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

Reduce

None of these

Increase

Equalize

13. The dry bulb temperature during sensible heating of air

None of these

Decreases

Remains constant

Increases

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

Ammonia

Fluorine

Carbon dioxide

Sulphur dioxide

15. The lowest thermal diffusivity is of

Iron

Rubber

Lead

Aluminium

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

R-12

Carbon dioxide

Lithium bromide

Sulphur dioxide

18. 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

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

It is not affected by the moisture present in the air

None of the above

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

The moisture present in it begins to condense

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

Wet vapour

Liquid

Saturated liquid

Sub-cooled liquid

Page 3 of 4

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

None of the above

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Is higher than that of the entering air

22. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Near critical pressure

Critical pressure of refrigerant

23. 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

24. A one tonne refrigerating machine means that

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

One tonne is the total mass of machine

One tonne of water can be converted into ice

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

Bigger

Smaller

Smaller/bigger depending on capacity

Equal

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

Higher critical temperature

Tow specific heat of liquid

High latent heat of vaporisation

High boiling point

27. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

Of freezing zone

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

5 to 7 TR

3 to 5 TR

1 to 3 TR

0.1 to 0.3 TR

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

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

It reacts with copper and its alloys.

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

Back pressure

Discharge pressure

Suction pressure

Critical pressure

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

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

None of these

32. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Evaporator

Receiver

Expansion valve

33. During heating and dehumidification process, dry bulb temperature

Increases

None of these

Decreases

Remains constant

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

High pressure liquid refrigerant

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

None of these

35. 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

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

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

Equal to critical temperature

None of the above

37. One ton of the refrigeration is

The refrigeration effect to produce 1 ton of ice at NTP conditions

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

38. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Total heat lines

Entropy lines

Temperature lines

39. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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