Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Compressor discharge

Receiver

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

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

Equal to critical temperature

None of the above

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

Low temperature at high altitudes

Low weight per tonne of refrigeration

High heat transfer rate

Higher coefficient of performance

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

None of these

Same

Less

5. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

None of these

Increases

6. One ton of the refrigeration is

The standard unit used in refrigeration problems

The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

The cooling effect produced by melting 1 ton of ice

The refrigeration effect to produce 1 ton of ice at NTP conditions

7. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

8. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

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

High boiling point

High latent heat of vaporisation

Higher critical temperature

Tow specific heat of liquid

10. Choose the correct statement

A refrigerant should have low latent heat

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

Pre-cooling and sub-cooling bf refrigerant are same

Page 2 of 4

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

Sub-cooled liquid

Wet vapour

Liquid

Saturated liquid

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

Smaller/bigger depending on capacity

Smaller

Bigger

Equal

13. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

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

Sub-cooled liquid region

None of these

Wet vapour region

Superheated vapour region

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

Equalize

Increase

None of these

Reduce

16. 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 goes into solution

Ammonia vapour is driven out of solution

17. The lowest thermal diffusivity is of

Aluminium

Rubber

Lead

Iron

18. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

All of these

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

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

Critical pressure

Suction pressure

Back pressure

Discharge pressure

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

Evaporator

Compressor

Condenser

Expansion valve

Page 3 of 4

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

It reacts with copper and its alloys.

All of these

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

22. 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

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

More/less depending on rating

Less

Same

24. 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

25. During heating and dehumidification process, dry bulb temperature

Remains constant

Increases

Decreases

None of these

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

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

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

Sulphur dioxide

Lithium bromide

Carbon dioxide

R-12

28. Carbon dioxide is

Odourless

Colourless

Non-flammable

All of these

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

Sulphur dioxide

Ammonia

Carbon dioxide

Fluorine

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

None of the above

Is higher than that of the entering air

Can be lower or higher than that of the entering air

Is lower than that of the entering air

Page 4 of 4

31. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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 refrigerant is used

One tonne of water can be converted into ice

32. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Pressure lines

Total heat lines

33. 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

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

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

None of the above

35. The optimum effective temperature for human comfort is

Not dependent on season

Same in winter and summer

Higher in winter than in summer

Lower in winter than in summer

36. 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

High, of the order of 25°

Zero

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

3 to 5 TR

0.1 to 0.3 TR

1 to 3 TR

5 to 7 TR

38. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is more than 1

Is less than 1

39. 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 secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

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

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

High pressure liquid refrigerant

Refrigeration & Air-Conditioning Practice Set-2

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