Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

None of these

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

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

Same

None of these

More

Less

3. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Expansion valve

Receiver

4. 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

5. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

6. 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 goes into solution

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

Increase

Reduce

None of these

Equalize

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

Reduced to a value below its critical temperature

Equal to critical temperature

Increased to a value above its critical temperature

None of the above

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

Simple evaporative air cooling system

All of these

Simple air cooling system

Bootstrap air cooling system

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

Compressor

Expansion valve

Evaporator

Condenser

Page 2 of 4

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

Back pressure

Suction pressure

Critical pressure

Discharge pressure

12. A one tonne refrigerating machine means that

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 of water can be converted into ice

One tonne refrigerant is used

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

More

Less

Same

More/less depending on rating

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

As low as possible (3 to 11°C)

Any value

High, of the order of 25°

Zero

15. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

Can be avoided by proper design

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

Smaller/bigger depending on capacity

Equal

Bigger

Smaller

17. Carbon dioxide is

Odourless

All of these

Colourless

Non-flammable

18. Choose the correct statement

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

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

A refrigerant should have low latent heat

19. 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

20. The lowest thermal diffusivity is of

Aluminium

Iron

Rubber

Lead

Page 3 of 4

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

Ammonia

Fluorine

Sulphur dioxide

Carbon dioxide

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

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

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

5 to 7 TR

1 to 3 TR

3 to 5 TR

0.1 to 0.3 TR

24. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

Increases power required per ton of refrigeration

All of these

25. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Pressure lines

Entropy lines

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

None of the above

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

27. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

None of these

29. 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

30. 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

After passing through the condenser

Before entering the expansion valve

Page 4 of 4

31. During heating and dehumidification process, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

Lithium bromide

Sulphur dioxide

Carbon dioxide

R-12

33. The dry bulb temperature during sensible heating of air

Decreases

None of these

Remains constant

Increases

34. 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 secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

35. One ton of the refrigeration is

The standard unit used in refrigeration problems

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 cooling effect produced by melting 1 ton of ice

36. 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.

37. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

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

Wet vapour

Liquid

Sub-cooled liquid

Saturated liquid

39. The optimum effective temperature for human comfort is

Same in winter and summer

Lower in winter than in summer

Higher in winter than in summer

Not dependent on season

40. The COP of a domestic refrigerator

Depends upon the make

Is equal to 1

Is less than 1

Is more than 1

Refrigeration & Air-Conditioning Practice Set-2

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