Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

(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

2. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Depends upon the make

Is less than 1

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

Wet vapour

Saturated liquid

Liquid

Sub-cooled liquid

4. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much below critical pressure

Much above critical pressure

Critical pressure of refrigerant

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

Smaller

Smaller/bigger depending on capacity

Equal

Bigger

6. Carbon dioxide is

Odourless

Colourless

All of these

Non-flammable

7. 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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

8. 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

Zero

High, of the order of 25°

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

R-12

Lithium bromide

Sulphur dioxide

Carbon dioxide

10. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

Page 2 of 4

11. The dry bulb temperature during sensible heating of air

Increases

Remains constant

None of these

Decreases

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

Fluorine

Sulphur dioxide

Carbon dioxide

Ammonia

13. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of cooling medium

Of freezing zone

Of evaporator

14. 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

15. 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

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

Back pressure

Suction pressure

Critical pressure

Discharge pressure

17. 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

After passing through the condenser

Before passing through the condenser

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

Sub-cooled liquid region

Superheated vapour region

None of these

Wet vapour region

19. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

20. 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

Equalize

Reduce

Increase

Page 3 of 4

21. 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

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

It is toxic to mucous membranes.

All of these

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

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

High boiling point

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

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

Simple evaporative air cooling system

Simple air cooling system

All of these

Bootstrap air cooling system

25. 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

Weak solution mixes with strong solution

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

Can be lower or higher than that of the entering air

Is higher than that of the entering air

None of the above

Is lower than that of the entering air

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

More

More/less depending on rating

Less

Same

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

Less

Same

More

None of these

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

Compressor

Expansion valve

Evaporator

Condenser

30. One ton of the refrigeration is

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 refrigeration effect to produce 1 ton of ice at NTP conditions

The cooling effect produced by melting 1 ton of ice

Page 4 of 4

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

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

Equal to critical temperature

None of the above

32. 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

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

It is not affected by the moisture present in the air

33. A one tonne refrigerating machine means that

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

One tonne is the total mass of machine

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

1 to 3 TR

0.1 to 0.3 TR

5 to 7 TR

3 to 5 TR

35. During heating and dehumidification process, dry bulb temperature

Remains constant

Decreases

Increases

None of these

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

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

Between the first heat exchanger and the secondary compressor

37. The lowest thermal diffusivity is of

Aluminium

Rubber

Iron

Lead

38. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Pressure lines

Total heat lines

Entropy lines

39. The higher temperature in vapour compression cycle occurs at

Evaporator

Receiver

Compressor discharge

Expansion valve

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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