Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Low temperature at high altitudes

High heat transfer rate

Low weight per tonne of refrigeration

Higher coefficient of performance

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

Less

More/less depending on rating

Same

More

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

1 to 3 TR

3 to 5 TR

0.1 to 0.3 TR

5 to 7 TR

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

Compressor

Evaporator

Condenser

Expansion valve

5. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Entropy lines

Total heat lines

Temperature lines

6. 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

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

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

8. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes solid

9. 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

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

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

Page 2 of 4

11. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is more than 1

Is less than 1

12. 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

Increase

Reduce

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

Equal

Smaller

Smaller/bigger depending on capacity

Bigger

14. Choose the correct statement

Superheat and sensible heat of a 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

Pre-cooling and sub-cooling bf refrigerant are same

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

16. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

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

Less

None of these

More

Same

18. Carbon dioxide is

Odourless

Non-flammable

Colourless

All of these

19. The optimum effective temperature for human comfort is

Higher in winter than in summer

Same in winter and summer

Not dependent on season

Lower in winter than in summer

20. 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 refrigeration effect to produce 1 ton of ice at NTP conditions

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

Page 3 of 4

21. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Near critical pressure

Critical pressure of refrigerant

Much below critical pressure

22. During heating and dehumidification process, dry bulb temperature

Increases

Remains constant

None of these

Decreases

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

Between the secondary compressor and the second heat exchanger

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

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

Tow specific heat of liquid

High latent heat of vaporisation

Higher critical temperature

High boiling point

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

Sulphur dioxide

R-12

Carbon dioxide

Lithium bromide

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

Sulphur dioxide

Carbon dioxide

Fluorine

Ammonia

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

Superheated vapour region

Sub-cooled liquid region

None of these

Wet vapour region

28. 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

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

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

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

None of the above

Is lower than that of the entering air

Is higher than that of the entering air

Can be lower or higher than that of the entering air

30. The higher temperature in vapour compression cycle occurs at

Receiver

Evaporator

Compressor discharge

Expansion valve

Page 4 of 4

31. The dry bulb temperature during sensible heating of air

Decreases

None of these

Increases

Remains constant

32. 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

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

The moisture present in it begins to condense

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

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

Critical pressure

Back pressure

Suction pressure

Discharge pressure

35. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Is immaterial

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

36. The lowest thermal diffusivity is of

Lead

Iron

Aluminium

Rubber

37. 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

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

All of these

Simple air cooling system

Bootstrap air cooling system

Simple evaporative air cooling system

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

High, of the order of 25°

As low as possible (3 to 11°C)

Zero

Any value

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

Sub-cooled liquid

Liquid

Wet vapour

Saturated liquid

Refrigeration & Air-Conditioning Practice Set-2

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