Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

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

Compressor

Evaporator

Expansion valve

Condenser

2. 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

3. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Much above critical pressure

Critical pressure of refrigerant

4. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Entropy lines

Temperature lines

Pressure lines

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

Less

Same

More/less depending on rating

6. 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

7. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid becomes solid

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

Superheated vapour region

None of these

Sub-cooled liquid region

Wet vapour region

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

Carbon dioxide

Ammonia

Fluorine

Sulphur dioxide

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

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

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11. The dry bulb temperature during sensible heating of air

None of these

Increases

Decreases

Remains constant

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

Reduced to a value below its critical temperature

None of the above

Increased to a value above its critical temperature

Equal to critical temperature

13. The COP of a domestic refrigerator

Depends upon the make

Is less than 1

Is equal to 1

Is more than 1

14. The lowest thermal diffusivity is of

Lead

Rubber

Aluminium

Iron

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

16. 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

17. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

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

Back pressure

Discharge pressure

Critical pressure

Suction pressure

19. During heating and dehumidification process, dry bulb temperature

None of these

Increases

Remains constant

Decreases

20. 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

Page 3 of 4

21. Choose the correct statement

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

Superheat and sensible heat of a refrigerant are same

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

None of the above

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

23. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

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

Same

Less

None of these

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

Bigger

Equal

Smaller

Smaller/bigger depending on capacity

26. 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

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

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

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

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

It reacts with copper and its alloys.

29. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

Of evaporator

At which refrigerant gas becomes liquid

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

Saturated liquid

Sub-cooled liquid

Wet vapour

Liquid

Page 4 of 4

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

All of these

Bootstrap air cooling system

Simple evaporative air cooling system

Simple air cooling system

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

High boiling point

Tow specific heat of liquid

High latent heat of vaporisation

Higher critical temperature

33. The higher temperature in vapour compression cycle occurs at

Evaporator

Compressor discharge

Receiver

Expansion valve

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

Increase

None of these

Equalize

Reduce

35. 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

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

R-12

Sulphur dioxide

Lithium bromide

Carbon dioxide

37. Carbon dioxide is

Colourless

Odourless

Non-flammable

All of these

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

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

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

Zero

High, of the order of 25°

Any value

As low as possible (3 to 11°C)

40. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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 of water can be converted into ice

Refrigeration & Air-Conditioning Practice Set-2

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