Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Smaller

Equal

Bigger

Smaller/bigger depending on capacity

2. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

3. 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

4. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne refrigerant is used

One tonne of water can be converted into ice

One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

5. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

Not dependent on season

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

5 to 7 TR

0.1 to 0.3 TR

3 to 5 TR

1 to 3 TR

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

8. Choose the correct statement

A refrigerant should have low latent heat

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

Pre-cooling and sub-cooling bf refrigerant are same

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

Zero

Any value

As low as possible (3 to 11°C)

High, of the order of 25°

10. The COP of a domestic refrigerator

Is less than 1

Is equal to 1

Depends upon the make

Is more than 1

Page 2 of 4

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

Critical pressure

Back pressure

Discharge pressure

Suction pressure

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

Simple air cooling system

All of these

Simple evaporative air cooling system

Bootstrap air cooling system

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

Higher critical temperature

Tow specific heat of liquid

High boiling point

High latent heat of vaporisation

14. 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

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

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

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

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

High pressure liquid refrigerant

17. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Much above critical pressure

Critical pressure of refrigerant

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

Liquid

Wet vapour

Saturated liquid

Sub-cooled liquid

19. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Pressure lines

Entropy lines

20. 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

Page 3 of 4

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

None of these

Same

Less

More

22. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of freezing zone

Of cooling medium

Of evaporator

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

Carbon dioxide

Sulphur dioxide

R-12

Lithium bromide

24. The evolution of heat of solution takes place in ammonia absorption plant when

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

25. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

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

Increase

Equalize

Reduce

None of these

27. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Evaporator

Expansion valve

28. The lowest thermal diffusivity is of

Lead

Iron

Rubber

Aluminium

29. 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 + 2

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

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

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

All of these

It is toxic to mucous membranes.

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

Page 4 of 4

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

High heat transfer rate

Higher coefficient of performance

Low temperature at high altitudes

Low weight per tonne of refrigeration

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

Carbon dioxide

Sulphur dioxide

Ammonia

Fluorine

33. During heating and dehumidification process, dry bulb temperature

None of these

Decreases

Increases

Remains constant

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

Sub-cooled liquid region

None of these

Superheated vapour region

Wet vapour region

35. 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

36. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

Increases

None of these

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

Expansion valve

Condenser

Evaporator

Compressor

38. 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

39. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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