Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

Same

Less

More

2. 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

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

Lithium bromide

Sulphur dioxide

R-12

Carbon dioxide

4. Condensing temperature in a refrigerator is the temperature

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

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

Equal to critical temperature

Reduced to a value below its critical temperature

None of the above

Increased to a value above its critical temperature

6. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

7. The COP of a domestic refrigerator

Is less than 1

Is equal to 1

Depends upon the make

Is more than 1

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

High, of the order of 25°

Zero

As low as possible (3 to 11°C)

Any value

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

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

None of these

10. 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

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11. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid will remain liquid

12. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

One tonne refrigerant is used

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

13. 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

14. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Pressure lines

Temperature lines

Total heat lines

15. The lowest thermal diffusivity is of

Aluminium

Lead

Rubber

Iron

16. 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

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

(C.O.P.)_P = (C.O.P.)_R + 2

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

Increase

None of these

Reduce

Equalize

19. One ton of the refrigeration is

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

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

20. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

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

Smaller

Equal

Smaller/bigger depending on capacity

Bigger

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

Expansion valve

Evaporator

Compressor

Condenser

23. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Expansion valve

Evaporator

24. The dry bulb temperature during sensible heating of air

Remains constant

Increases

Decreases

None of these

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

Between the secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

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

High boiling point

High latent heat of vaporisation

Higher critical temperature

Tow specific heat of liquid

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

Back pressure

Critical pressure

Discharge pressure

Suction pressure

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

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

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

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

Low pressure vapour refrigerant

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

Fluorine

Ammonia

Sulphur dioxide

Carbon dioxide

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

It is toxic to mucous membranes.

All of these

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

32. Carbon dioxide is

Non-flammable

All of these

Colourless

Odourless

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

Wet vapour

Liquid

Saturated liquid

Sub-cooled liquid

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

The moisture present in it begins to condense

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

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

Less

None of these

More

Same

36. Choose the correct statement

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

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

37. 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

38. During heating and dehumidification process, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

High heat transfer rate

40. The optimum effective temperature for human comfort is

Not dependent on season

Lower in winter than in summer

Same in winter and summer

Higher in winter than in summer

Refrigeration & Air-Conditioning Practice Set-2

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