Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

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

Increased to a value above its critical temperature

Equal to critical temperature

Reduced to a value below its critical temperature

None of the above

3. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

All of these

Increases power required per ton of refrigeration

4. 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

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

Critical pressure

Discharge pressure

Suction pressure

Back pressure

6. The optimum effective temperature for human comfort is

Same in winter and summer

Not dependent on season

Higher in winter than in summer

Lower in winter than in summer

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

Sub-cooled liquid

Saturated liquid

Wet vapour

Liquid

8. 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

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

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

Simple air cooling system

10. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Depends upon the make

Is equal to 1

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

It is toxic to mucous membranes.

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

12. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Near critical pressure

Much above critical pressure

13. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

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

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

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

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

More

Same

Less

More/less depending on rating

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

Carbon dioxide

Ammonia

Fluorine

Sulphur dioxide

17. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Receiver

Evaporator

18. Formation of frost on evaporator in refrigerator

Is immaterial

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Increases heat transfer rate

19. The dry bulb temperature during sensible heating of air

Increases

Decreases

Remains constant

None of these

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

Smaller/bigger depending on capacity

Bigger

Smaller

Equal

Page 3 of 4

21. During heating and dehumidification process, dry bulb temperature

Remains constant

None of these

Decreases

Increases

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

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

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

As low as possible (3 to 11°C)

Zero

Any value

High, of the order of 25°

24. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

25. The lowest thermal diffusivity is of

Aluminium

Rubber

Iron

Lead

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

None of these

Reduce

Equalize

Increase

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

None of these

Superheated vapour region

Wet vapour region

Sub-cooled liquid region

28. Carbon dioxide is

Non-flammable

Odourless

Colourless

All of these

29. Choose the correct statement

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

Superheat and sensible heat of a refrigerant are same

A refrigerant should have low latent heat

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

Is higher than that of the entering air

None of the above

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Page 4 of 4

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

High heat transfer rate

Higher coefficient of performance

Low weight per tonne of refrigeration

Low temperature at high altitudes

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

Evaporator

Condenser

Compressor

Expansion valve

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

Tow specific heat of liquid

Higher critical temperature

High boiling point

High latent heat of vaporisation

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

1 to 3 TR

5 to 7 TR

0.1 to 0.3 TR

3 to 5 TR

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

36. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes vapour

37. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Entropy lines

Pressure lines

Temperature lines

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

Less

None of these

More

Same

39. 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

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

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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