Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. Carbon dioxide is

Odourless

Non-flammable

All of these

Colourless

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

Zero

As low as possible (3 to 11°C)

Any value

High, of the order of 25°

3. 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

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

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

All of these

5. One ton of the refrigeration is

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

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

6. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is more than 1

Is equal to 1

7. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of evaporator

Of freezing zone

Of cooling medium

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

Back pressure

Suction pressure

Critical pressure

Discharge pressure

9. 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

10. The higher temperature in vapour compression cycle occurs at

Receiver

Expansion valve

Evaporator

Compressor discharge

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

Same

Less

More/less depending on rating

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

Reduce

Equalize

None of these

Increase

13. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

14. The dry bulb temperature during sensible heating of air

None of these

Remains constant

Increases

Decreases

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

None of the above

It is not affected by the moisture present in the air

The moisture present in it begins to condense

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

16. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

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

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

High heat transfer rate

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

18. 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

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

Low pressure vapour refrigerant

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

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

None of the above

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Is higher than that of the entering air

Page 3 of 4

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

Simple evaporative air cooling system

Bootstrap air cooling system

Simple air cooling system

All of these

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

Wet vapour region

None of these

Sub-cooled liquid region

Superheated vapour region

23. 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

24. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

All of these

25. 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

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

Smaller/bigger depending on capacity

Bigger

Smaller

Equal

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

Liquid

Sub-cooled liquid

Saturated liquid

Wet vapour

28. 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

29. The lowest thermal diffusivity is of

Aluminium

Iron

Rubber

Lead

30. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Is immaterial

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Page 4 of 4

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

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

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

None of these

Less

Same

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

Evaporator

Condenser

Compressor

Expansion valve

34. 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

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

36. During heating and dehumidification process, dry bulb temperature

Remains constant

Decreases

Increases

None of these

37. 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

38. 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

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

Carbon dioxide

Ammonia

Sulphur dioxide

Fluorine

40. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Pressure lines

Entropy lines

Refrigeration & Air-Conditioning Practice Set-2

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