Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. 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

2. 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

3. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Pressure lines

Entropy lines

4. 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

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

Is lower than that of the entering air

None of the above

Is higher than that of the entering air

Can be lower or higher than that of the entering air

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

Same

Less

None of these

7. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

Of freezing zone

8. 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 of water can be converted into ice

One tonne refrigerant is used

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

Compressor

Condenser

Evaporator

Expansion valve

10. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

All of these

Page 2 of 4

11. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Expansion valve

Receiver

Evaporator

12. 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

13. The lowest thermal diffusivity is of

Rubber

Lead

Aluminium

Iron

14. 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

Reduce

Equalize

Increase

15. 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

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 + 1

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

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

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

All of these

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

It is toxic to mucous membranes.

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

Critical pressure

Back pressure

Suction pressure

Discharge pressure

19. During heating and dehumidification process, dry bulb temperature

None of these

Increases

Decreases

Remains constant

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

None of these

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

Page 3 of 4

21. 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

Pre-cooling and sub-cooling bf refrigerant are same

Superheat and sensible heat of a refrigerant are same

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

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

None of these

High pressure liquid refrigerant

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

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

Wet vapour

Saturated liquid

Sub-cooled liquid

Liquid

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

Bootstrap air cooling system

Simple air cooling system

Simple evaporative air cooling system

All of these

26. 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

27. 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

Zero

High, of the order of 25°

28. The optimum effective temperature for human comfort is

Lower in winter than in summer

Same in winter and summer

Not dependent on season

Higher in winter than in summer

29. Carbon dioxide is

Non-flammable

Colourless

Odourless

All of these

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

0.1 to 0.3 TR

5 to 7 TR

1 to 3 TR

3 to 5 TR

Page 4 of 4

31. The dry bulb temperature during sensible heating of air

Increases

Remains constant

Decreases

None of these

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

Carbon dioxide

Sulphur dioxide

Ammonia

Fluorine

33. Formation of frost on evaporator in refrigerator

Is immaterial

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

34. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Equal

Smaller/bigger depending on capacity

Smaller

Bigger

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

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

Between the combustion chamber and the first heat exchanger

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

High boiling point

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

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

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

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

Same

More/less depending on rating

Less

40. The COP of a domestic refrigerator

Depends upon the make

Is more than 1

Is less than 1

Is equal to 1

Refrigeration & Air-Conditioning Practice Set-2

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